The production of code-mixed discourse 
David SANKOFF 
Centre de recherches math~matiques, Universit@ de Montr@al 
CP 6128 Succursale Centre-Ville 
Montr@al, Qudbec H3C 3J7 
sankoff@ere.umontreal.ca 
Abstract 
We propose a comprehensive theory of code- 
mixed discourse, encompassing equivalence- 
point and insertional code-switching, palin- 
dromic constructions and lexical borrowing. 
The starting point is a production model 
of code-switching accounting for empirical 
observations about switch-point distribution 
(the equivalence constraint), well-formedness of 
monolingual fragments, conservation of con- 
stituent structure and lack of constraint be- 
tween successive switch points, without invok- 
ing any "code-switching grammar". Code- 
switched sentence production makes alternate 
reference to two virtual monolingual sentences, 
one in each language, and is based on conser- 
vative conditions on language labeling of con- 
stituents, together with a constraint against 
real-time "look-ahead" from one code-switch to 
the next. Selective weakening of model condi- 
tions can produce (i) the type of palindromic 
(or portmanteau) construction occasionally oc- 
curring e.g., in switches between prepositional 
and postpositional languages, (ii) the switch- 
ing by "insertion" of very specific kinds of con- 
stituent reported e.g., for French noun phrases 
in switching with Arabic and, most important, 
(iii) lexical borrowing. Borrowing can create 
ambiguity as to language membership of sen- 
tence items, but the model predicts where this 
can be resolved, and the confirmation of these 
predictions, based on empirical studies of inflec- 
tional morphology, validates key aspects of the 
model. 
Introduction 
Communities of bilinguals tend to evolve a con- 
versational mode where elements of both lan- 
guages appear in the same interaction and even 
in the same sentence despite the fact that all 
participants may be competent in either of the 
two languages. Whether this mode is used in 
preference to monolingual discourse depends on 
the type of interaction, the participants, the 
subject of conversation and many other fac- 
tors. The grammatical nature of code-mixed 
discourse, however, tends to be very specific 
to the community and varies widely among 
bilingual communities, even among communi- 
ties which share the same pair of languages. 
Empirical research has isolated four clearly dis- 
tinct processes which may be responsible for 
mixing to different extents in different commu- 
nities -- code-switching, nonce borrowing, spe- 
cialized incorporation and interference. None 
of these processes requires the deformation, al- 
teration or convergence of either of the two con- 
stituent languages at the syntactic, lexical, mor- 
phological, phonological, or semantic levels at 
the moment the mixing occurs. Except for code- 
switching, however, they may all lead in the long 
term to lexical expansion in one or both of the 
languages. 
This paper is a contribution to a coherent for- 
mal account of code-mixing which integrates all 
of these processes 1, though only code-switching 
and borrowing will be considered here. This 
is based on a series of empirical studies which 
now allows us to distinguish between them 
structurally and quantitatively. Our starting 
point will be a recent formal characterization 
of a equivalence-point code-switching (Sankoff, 
1The analysis of code-mixing is a controversial sub- 
ject with respect to several aspects: Is all code-mixing 
-- borrowing, switching, interference -- really the same 
process? Do languages involved in code-mixing tend to 
converge syntactically? Are patterns of code-mixing pre- 
dictable or explicable by theories of (monolingual) gram- 
mar? We assume a negative response to all these ques- 
tions and refer to the literature for more detailed discus- 
sion. 
1998). We will then extend this to two rarer 
code-switching mechanisms, and finally to lexi- 
cal borrowing, the most frequent type of code- 
mixing. 
1 Code-switching 
1.1 "The facts" 
The modern motivation for studying code- 
switching was initially to explain the obser- 
vation that in bilingual communities, speakers 
tend to switch from one language to another in- 
trasententially at certain syntactic boundaries 
and not at others (Gumperz & Hernandez, 
1969). The first general explanation to account 
for this distribution was Poplack's (1978, 1980) 
argument that switching should be favored at 
the kinds of syntactic boundaries which occur 
in both languages, thus avoiding word order 
that might seem unnatural according to one 
or both grammars: the equivalence constraint 
(see also Lipski, 1977; Pfaff, 1979). Despite 
criticism of this approach (Rivas, 1981; Wool- 
ford, 1983; Di Sciullo et al., 1986; Pandit, 1990; 
Myers-Scotton, 1993; Belazi et al., 1994; Ma- 
hootian & Santorini, 1994), it has been suc- 
cessfully used to account for code-switching in 
Spanish-English (Poplack, 1978,1980), Finnish- 
English (Poplack et al., 1987b), Arabic-French 
(Na'it M'Barek & Sankoff, 1988), Tamil-English 
(Sankoff et al., 1990), Fongbe-French (Meechan 
& Poplack, 1995), Wolof-French (Poplack & 
Meechan, 1995), Igbo-English (Eze, 1997) and 
many other bilingual communities. 
Other fundamental facts about code-switched 
sentences include the well-formedness of mono- 
lingual fragments within such sentences -- true 
whether a fragment constitutes a complete con- 
stituent or stretches across two or more (possi- 
bly incomplete) constituents, the conservation 
of constituent structure, and the unpredictability 
of switching -- even if we can determine where 
a code-switch can occur and where it cannot, 
there is no way of knowing in advance for any 
site whether a switch will occur there or not. In 
particular, if a switch occurs at some point in 
a sentence, this does not constrain any poten- 
tial site(s) later in the sentence either to contain 
another switch or not to -- there are no forced 
switches. 
1.2 A production approach 
We do not assume that the mechanisms of 
switching from one language to another can be 
deduced entirely from the general principles of 
monolingual grammars 2. Thus we do not an- 
alyze the distribution of intrasentential switch 
points in terms of a grammar of any of the 
types ordinarily used for accounting for single 
languages, but by means of a left-to-right pro- 
cess that refers to two well-formed monolingual 
sentences (i.e. each satisfying the constraints 
of an "ordinary" monolingual grammar for one 
of the two languages) in producing monolingual 
sentence fragments and in evaluating potential 
switch points between these fragments. 
Our model is based on the assumption that 
bilinguals are fully competent in their two lan- 
guages, that there is no convergence of the two 
monolingual codes even during bilingual dis- 
course, and that a code-switched sentence con- 
sists of fragments of two monolingual sentences 
(each one a translation of the other) pieced to- 
gether. This is done first through an other- 
wise unconstrained production model that sim- 
ply copies part of one monolingual process fol- 
lowed by part of the other in such a way that 
constituent structure is conserved. The result- 
ing process satisfies neither equivalence nor un- 
predictability. By adding two very simple rules 
for labeling some constituents according to their 
language, the existence of a consistent labeling 
-- which can be easily monitored during real- 
time linear production -- turns out to guaran- 
tee both equivalence and, for most situations, 
unpredictability. 
2While formal theories of grammar may well account 
for monolingual language in terms of general linguistic 
principles, there is no reason to believe that processes 
which juxtapose two languages can be explained in ex- 
actly the same way. The reasons implicit or explicit in 
attempts to do so have to do with explanatory economy, 
either of individual linguistic competence or of linguistic 
theories. This seems specious since both are based on a 
notion of a "hard-wired" human linguistic faculty evolv- 
ing in prehistoric monolingualism. Experience in widely 
diverse speech communities suggests instead that code- 
mixing strategies, including code-switching, evolve in the 
life-time of particular communities, are only partly de- 
pendent on linguistic typology of the two languages and 
exhibit widely different patterns of adapting monolingual 
resources for incorporating linguistic innovation. 
1.3 Hierarchy and linearity. 
That monolingual fragments are not co- 
extensive with entire constituents is problem- 
atic for any model relying on hierarchical re- 
lations for deciding well-formedness, since such 
models are designed primarily to ensure well- 
formedness of entire constituents, monolingual 
or bilingual. They cannot ensure that adja- 
cent same-language parts of neighboring con- 
stituents are compatible (i.e. yield a well- 
formed fragment when juxtaposed), since these 
parts may not even be in the same language as 
the rest of the constituents that contain them 
(Muysken, 1995). For example, an earlier model 
(Sankoff & Mainville, 1986), using the context- 
free grammars of two languages to account for 
code-switched sentences satisfying the equiv- 
alence constraint, could not ensure the well- 
formedness of monolingual fragments, for the 
very reason Muysken has pointed out. 
This problem is at the core of the conflict be- 
tween hierarchical and linear modes of explana- 
tion. We will resolve it by ascribing ultimate 
responsibility for the well-formedness of mono- 
lingual fragments to production-level processes. 
These fragments, arbitrary substrings of pre- 
constructed well-formed monolingual sentences, 
are pieced together during linear production in 
a way which corresponds to the other general 
observations about code-switching and which is 
essentially neutral with respect to theories of 
monolingual grammar. 
1.4 The syntactic model 
We are interested in seeing how two hierarchi- 
cally structured languages resolve their word- 
order differences during intrasentential code- 
switching, without the confounding effects of 
other linguistic phenomena. Thus we will con- 
struct a model where the only differences be- 
tween two languages have to do with word 
order and the (phonological) form of lexical 
items, and work out the logical consequences 
for code-switching of various assumptions and 
constraints on the production of bilingual sen- 
tences. Linearity and hierarchy are the key 
structural aspects here 3, and the simplest class 
Sin focusing on the relationship between word order 
and hierarchy, we are choosing a model not adapted to 
the treatment of tags and moveable elements such as 
many adverbials (whose "switchability" is uncontrover- 
of recursive grammars accommodating these 
properties is that of context-free grammars. 
Consider a context-free grammar consisting 
of a set C of "categories" or non-terminal sym- 
bols, including one distinguished symbol s (for 
"sentence"); a set of terminal symbols T ("lex- 
ical slots"), none of which are also in C, a lex- 
icon L which is basically a set of words and an 
indication of the kind of lexical slot each word 
can fill, and a set of rewrite rules R of form 
c --~ vl -"vn where c is a symbol in C', and the 
string on the right hand side vl...vn consists 
of one or more symbols in T or C. A sentence 
is derived by writing s, then rewriting s by the 
string Ul'"um on the right hand side of any 
rule in R of form s -~ ul".um, then rewrit- 
ing any ui which is non-terminal by some rule 
of form ui --~ wl...wp and so on. Whenever a 
lexical slot appears in the string it can be filled 
with words of the appropriate category from L. 
When there are no more non-terminal symbols 
(and R must be such that this is always possi- 
ble), the derivation stops, and the current string 
is just a sentence generated by the grammar. 
We will make use of phrase structure tree rep- 
resentation for sentences and their constituents. 
Each symbol appearing in the derivation is rep- 
resented by a node of the tree; it dominates 
the constituent of which it is the highest node, 
and may be used to represent that constituent. 
(Each terminal node is itself a constituent.) 
Note that the words in each constituent form 
a (contiguous) substring of the sentence. We de- 
fine these, and all other contiguous substrings of 
a well-formed sentence string to be well-formed 
fragments. 
In order to speak of code-switching between 
two different grammars, it is necessary to have 
some connection between the categories of one 
and the categories of the other 4. We make 
sial), nor of remote relationships such as discontinuous 
constituents, internal co-reference, etc., whose effects on 
code-switching, if any, have never been systematically 
documented. On the other hand, context-sensitive phe- 
nomena such as subcategorization (Bentahila ~ Davies, 
1983), cliticization or certain deletion processes also es- 
cape the scope of context-free modeling, as do other null 
elements, agreement rules and other features which may, 
in particular communities, be important to understand- 
ing switch sites (Muysken, 1995). 
4In natural languages, such correspondences will usu- 
ally be imperfect (Muysken, 1995), but this is peripheral 
to our interest in word order. 
10 
the strong assumptions of lexical translatability 
and categorial congruence, meaning that there 
is a one-to-one correspondence between the lex- 
icon LA of language A and the lexicon LB of 
language B, though the words are all recog- 
nizable as coming from one language or the 
other. We use the same categories C and lex- 
ical slots T for both languages. Furthermore 
we assume grammatical congruence: there is a 
one-to-one connection between the rulesRA of 
language A and RB of language B -- if RA 
contains a rule c ~ Vl""Vn, then RB must 
contain a rule c --+ Ul...~Zn, where each sym- 
bol in Vl""Vn has its counterpart in Ul'"un, 
and vice-versa, though the order of the terms 
in one string will not in general correspond to 
the order of the terms in the other. Finally, 
for convenience, we will assume fixed word or- 
der, that is if c --r Vl... vn in a given grammar, 
then there may be other rules rewriting C in 
that grammar, but none where the right hand 
side contains exactly the same set of symbols 
U1, • • ",~3n. 
To simplify our presentation in this article, 
we do not allow ambiguity in our grammars. 
Not only must each monolingual sentence be 
derivable in exactly one way, but each rule may 
contain any one symbol only once on its right 
hand side. These conditions may be relaxed, as 
long as there is a way of identifying correspond- 
ing symbols in corresponding rules in the two 
grammars. 
In comparing the structure of two sentences, 
we say that they have the same constituent 
structure if there is a one-to-one correspondence 
between their constituents such that if x in one 
sentence corresponds to y in the other, then the 
(unordered) set of subconstituents of x corre- 
sponds to the set of subconstituents of y. 
The consequences of our assumptions are 
summarized in: 
Theorem 1 5 Every sentence in language A 
has a unique counterpart in language B with 
the same constituent structure and whose lexical 
items are translations o/ those in the sentence 
o/language A. 
Examples (la,b) are two (fictitious) sentences 
in English and French which we may imagine to 
be counterparts of each other according to some 
5Proofs of all theorems are given in Sankoff (1998) 
grammatical analysis of the two languages, in 
the sense of Theorem 1: 
Despite differences in word order, the con- 
stituent structure is identical and the lexical 
items are word-for-word translations (without 
quibbling about the questionable lexical status 
of the reflexive clitic and the genitive particle 
and the somewhat different internal structure 
of determiner in the PP). 
D N V pro PP 
D ~'~ NP 
The brothers wash themselves with some of Grandma's remarkable soap 
(lb) .......... S ~VP 
i I I~ ~es se l~ent avec du ~lvon rem~uable de grand-maman 
1.5 The production model. 
In the model, the production of a code-switched 
sentence presupposes the existence of two vir- 
tual sentences, one in language A and one in 
language B, counterparts of each other as in 
Theorem 1. For each 6 of (2a,b,c,d) the pair of 
virtual sentences is the one illustrated in (la,b). 
(2a) The brothers wash themselves I avec du 
savon remarquable de grand-maman 
(2b) Les fr~res se lavent I with some of Grand- 
ma's remarkable soap 
(2c) The brothers I se lavent avec I some of 
Grandma's remarkable soap 
(2d) The ( fr~res I wash themselves I avec I some 
of Grandma's remarkable soap 
Given the two virtual sentences in languages A 
and B, the code-switched sentence is produced 
by taking part of one of them, followed by part 
°Our examples of English/French mixing in this pa- 
per are fabricated, and their well-formedness (or not) 
asserted, solely to illustrate our arguments; they do not 
constitute empirical data. 
11 
of the other, and so on, without using any word 
(or its translation) more than once, until every 
lexical element (or its translation) has been used 
up. 
The idea of using virtual sentences is an ex- 
tension of concepts implicit in Poplack's origi- 
nal discovery (1978, 1980) of the importance of 
equivalence sites to code-switching and is what 
distinguishes it from attempts to account for 
code-switching using purely distributional data 
-- examples of sentences thought to be either 
well-formed or not. It implies the comparison 
of the sentence actually produced with what 
"could have been said" in either of the monolin- 
gual modes. Though the comparative data are 
of course not directly accessible, since only one 
sentence is uttered, controlled inference about 
unrealized possibilities is consistent with rigor- 
ous methodology (cf the notion of the linguistic 
variable (Labov, 1969; Sankoff, 1988). 
Postulating two complete virtual sentences, 
however, is an analytical convenience. All that 
would really be needed in a more realistic (and 
complicated) analysis, are the parts of each 
sentence that are actually used plus some ad- 
ditional details about the constituent within 
which a switch occurs. The consequences of 
this device, and its realism, lie largely in the 
way the monolingual fragments are produced 
"on the fly" by the monolingual grammars, how- 
ever these grammars are conceived in theory. 
Indeed, we need not refer to any particular lin- 
guistic theory for this aspect. 
The above process produces not only plausi- 
ble code-switched sentences such as those in (2), 
but also any combination of elements in any or- 
der as in (3). 
(3) de grand-maman \[the with \[ remarquable 
fr~res \[ soap themselves wash some of 
To arrive at an empirically and conceptually 
satisfactory model, we must add constraints. 
The first constraint is motivated by the empiri- 
cal observation that each monolingual fragment 
in bilingual discourse tends to be well-formed 
in its lexifier language. We will assume that the 
production of the sentence starts with a word in 
(either) one of the virtual sentences, and copies 
successive words from left to right in that sen- 
tence without skipping any until there is a code- 
switch to some word in the other virtual sen- 
tence. From this point in the other virtual sen- 
tence, production continues from left to right, 
and so on. When the left-to-right production 
arrives at a word (such as se after fr~res in ex- 
ample 4) which has already been used in the 
current or the other language (also some of af- 
ter with) or at the end of one of the virtual sen- 
tences, there must be a switch to the other vir- 
tual sentence or, if all the words have been used 
(after remarkable), the production must stop. 
(4) du savon \[ wash themselves with \[ les fr~res 
\[ Grandma's remarkable 
Theorem 2 The monolingual fragments in a 
code-switched sentence produced by left-to-right 
copying are well-formed. 
The left-to-right assumption ensures that mono- 
lingual fragments are well-formed, as illustrated 
in (4), as well as (2). By itself, however, it 
does not constrain how the alternating frag- 
ments in one language and the other are related; 
indeed it allows them to be juxtaposed in any 
order, as long as the fragment languages alter- 
nate; sister elements in the same constituent in 
a virtual sentence may find themselves remote 
from each other in the code-switched sentence, 
as with remarkable and savon in example (4). 
As mentioned in Section 1.1, however, empiri- 
cal research confirms that constituent structure, 
insofar as content and embedding or nesting re- 
lations are concerned, is conserved even if the 
constituent contains a code-switch. 
To conform to this observation, we make a 
second assumption, that once the production 
process enters or switches into a constituent, 
it must exhaust all the lexical slots in the con- 
stituent, in one language or both, before return- 
ing into a higher-level constituent or entering a 
sister constituent. In other words, each time it 
enters a deeper, or more nested, subconstituent, 
it cannot exit from it until that subconstituent 
is exhausted. Note that this assumption is in- 
dependent of whether or not the production fol- 
lows the left-to-right process described above, so 
that the sentence (5) satisfies nested first, but 
not left-to-right. 
(5) (wash((some of (Grandma's soap remark- 
able)) with) themselves) \[ (fr~res les) 
Theorem 3 Lexicalizing constituents accord- 
ing to nested-first is a sufficient condition for 
12 
conserving the same constituent structure in the 
code-switched sentence as in the two virtual sen- 
tences. 
The nested first condition and the left-to-right 
assumption are independent, in the sense that 
neither implies the other, as is clear from (4) 
and (5). Neither excludes the other, and to- 
gether, as in (6) and (2), they produce code- 
switched sentences with well-formed monolin- 
gual fragments and the same constituent struc- 
ture as the virtual sentences. 
(6a) (se lavent I (with (some of (Grandma's re- 
markable soap)))) I (les fr~res) 
(6b) (fr~res I the) I ((avec I (some of (Grandma's 
I savon remarquable))) I wash themselves ) 
1.6 The language of constituents and 
subconstituents. 
The model in Section 1.5, though it produces 
sentences like those in (2) and (6) with some de- 
sirable properties, is not complete. With only 
the two conditions, certain configurations may 
occur, such as those in (6), that are clearly 
unrealistic. For example, if the monolingual 
fragment being copied includes a word which 
must be positioned finally in a constituent, like 
fr~res in (6b), and if the words of the con- 
stituent in one virtual sentence or the other 
have not yet been used up, then an immediate 
code-switch, to the in this instance, is obliga- 
tory to satisfy nested first- the monolingual 
fragment cannot continue, even though it may 
have a natural continuation into another con- 
stituent. This, and other instances of forced 
code-switching, are clearly not phenomena ob- 
served in real bilingual discourse. 
Another type of construction not found in 
natural bilingual corpora but permitted in the 
simple production model might include a code- 
switched sentence which begins with a fragment 
of the virtual sentence in language A which 
would never occur in sentence-initial position in 
monolingual discourse in language A, such as se 
lavent in (6a). More generally, if there are sev- 
eral sister subconstituents in a constituent, they 
may be permuted in any order, as long as there 
is a switch between each adjacent pair. Still an- 
other anomalous output from this model, even 
if the two monolingual grammars contrast com- 
pletely, is a code-switch between every adjacent 
pair of words in the sentence. 
Thus the output of the production process as 
is hitherto formulated seems unduly constrained 
from the production point of view (by forcing 
switches) and not constrained enough from the 
perspective of the output structure. We thus 
come to the main point of this section: short of 
the equivalence constraint itself, can we moti- 
vate some constraint to account for the obser- 
vation that switching occurs almost exclusively 
at equivalence points (notion to be formalized 
in Section 1.6.1) and virtually all equivalence 
points seem to be eligible switch points? And 
can this be done in such a way that during pro- 
duction, the model speaker avoids any switch- 
ing which will obligatorily require compensatory 
switches later on in the sentence construction 
(switch planning or forcing)? Furthermore, can 
we do this without referring to facts of partic- 
ular languages, properties of particular gram- 
matical categories, or even the mechanisms of 
particular theories of monolingual grammar? 
Our approach to this problem is to postu- 
late a limited degree of structural monitoring. 
Monitoring the monolingual fragments for well- 
formedness is uncontroversial, and we need not 
enter into the details. What we propose for 
monitoring at the switch points is the "language 
label" of the constituent in which the switch oc- 
curs and of its immediate subconstituents. 
We first ask: what parts of the constituent 
structure of the code-switched sentence may be 
with certainty ascribed to one language or the 
other only, and hence should be labeled accord- 
ingly? Certainly (i) all terminal symbols -- lexi- 
cal slots -- are labeled according to whether the 
word filling the slot comes from LA or LB, since 
all words are identifiable as to their language, by 
definition in our model of congruent grammars. 
(ii) At the constituent level, any constituent, all 
of whose immediate subconstituents have the 
same label, should itself have this label. Any- 
thing else would be inconsistent. We will pro- 
pose a third criterion for labeling constituents, 
but we first prove the following" 
Theorem 4 Any non-terminal node carrying a 
label must have at least one immediate descen- 
dant node which has this same label or is un- 
labeled, and one descendant (possibly a lexical 
slot) which has the same label. 
Different instantiations of this model may ac- 
tually specify that certain subconstituents "in- 
13 
herit" the label -- in one theory the determiner 
may inherit the label of the noun phrase, in an- 
other theory it may be the noun itself. 
Requirement (ii) depends on constituent con- 
tent, but not on constituent order, so that it 
applies meaningfully to any sentence satisfying 
nested first such as (5) or (6b). The labeling of 
(6b) is illustrated in (7). 
jS 
N(F) D(E) 
i 
fr~res the avec some of Grandma's sawn rem~Nuable wash themselves 
To constrain the order, we are motivated to 
try to exclude situations such as a declarative 
sentence which begins with a well-formed verb 
phrase entirely in English followed by a subject 
noun phrase in another language. More gener- 
ally, (iii) any subconstituent which is out of rank 
order position among its sister subconstituents 
according to one of the languages, must receive 
the label of the other language. For example, if 
the languages A and B are SVO and VSO, re- 
spectively, and the code-switched sentence has 
order VSO, then the labeling should be vBsBo; 
if the code-switched sentence were SOV, then 
condition (iii) could not be satisfied, since O is 
out of order according to both languages, as is 
the V. 
If conditions (i)-(iii), all of which are well- 
motivated, cannot be simultaneously satisfied, 
the code-switched sentence cannot be consid- 
ered well-formed. Thus in our hypothetical 
example with a sentence-initial English verb 
phrase, requirements (ii) and (iii) conflict, so 
the sentence is not well-formed. And in exam- 
ple (7) condition (iii) cannot be satisfied with 
respect to any of the categories lexicalized by 
fr&es, the, savon, remarquable, wash and them- 
selves, nor the PP node -- according to the ex- 
tremely constrained grammars responsible for 
examples (la,b). On the other hand, each of 
examples (2a,b,c,d) satisfy all of the conditions 
(i)-(iii). 
All that a speaker monitors is the language 
label of the constituent in which a potential 
switch occurs and that of its subconstituents. 
No additional labeling is warranted within 
this framework, though other treatments of 
code-switching all have their own particular way 
of assigning a label to each and every con- 
stituent (Rivas, 1981; Woolford, 1983; Joshi, 
1985; Di Sciullo et al., 1986; Myers-Scotton, 
1993). In particular, we would claim that there 
is no conceptual justification or need for postu- 
lating an underlying (or "matrix") language for 
the entire sentence itself when this is not moti- 
vated by criteria (ii) and (iii). 
1.6.1 The equivalence constraint. 
In the string of words which constitute a code- 
switched sentence in our model, there is no 
problem in identifying where a fragment in lan- 
guage A stops and one in language B starts. On 
the constituent level, however, it is not as ob- 
vious where this switch should be located and 
sometimes even whether or not there is an inter- 
constituent switch, as in (8). 
(8) J S(E)._ .._......~) ---- ~- VP(E) 
D~E) ~ V(E) NI~E) 
\[ AD(~) N(E~ \[ D~E) N(E) / l, I:o,,o / I 
The original Duke \[ de Lorraine \[ had 10 000 men 
This is an example of string-level code-switching 
with and without corresponding constituent- 
level switches. The rule NP--+ ADJ+NP in En- 
glish and NP-~ NP+ADJ in French results in 
the lowest NP being labeled E, by requirement 
(iii). The higher NPs, the VP, the object NP 
and the S are labeled E, and the PP labeled 
F because all of their subconstituents are (re- 
quirement (ii)). The code-switch between Duke 
and de is also a constituent-level switch between 
Duke and the PP, but the switch between Lor- 
raine and had is not reflected by a switch be- 
tween the highest NP and its sister VP since 
they are both labeled E. 
In general, what constitutes a code-switch be- 
tween two adjacent sister constituents? The 
only reasonable answer is that one constituent is 
labeled A and the other B. What happens if two 
differently labeled sister constituents are sepa- 
rated by one or more unlabeled constituents? 
Once again it is clear that there has been a code- 
14 
switch at the constituent level, but the site can- 
not be pinned down, other than by saying that 
it occurred in the interval between the two la- 
beled constituents. Note that there also must 
be switches at some lower levels within each of 
the intervening unlabeled constituents; other- 
wise they could not be unlabeled, by criterion 
(ii). 
We can now state the equivalence constraint. 
Consider the corresponding rules for ordering 
the n subconstituents of a given constituent in 
language A and language B. If the sets of the 
first i symbols on the right-hand side of the rules 
are different in the two grammars (and hence 
the set of the last n - i symbols are also differ- 
ent, since the two rules are congruent), then the 
equivalence constraint prohibits a code-switch 
between the i-th and i + 1-st subconstituents. 
Otherwise the boundary between the two sub- 
constituents is an equivalence point and a code- 
switch is permitted. In the case n = 2, this 
reduces to the prohibition of a code-switch be- 
tween the two subconstituents unless the two 
languages order them in the same way. 
1.7 Proof of the equivalence constraint. 
The production model in Section 1.5 and the 
labeling rules in Section 1.6 ensure that mono- 
lingual fragments are well-formed, constituent 
structures are correct and that no constituent 
labeled X appears within a higher constituent 
in a rank order position not permitted in lan- 
guage X. This does not mean that the equiv- 
alence constraint holds. Consider for example 
the rules c --~ xyz and c --+ zyx in languages 
A and B respectively. Then the model as it is 
now constituted would permit the constituent 
order xAyBz A, with two constituent-level code- 
switches, both of which violate the equivalence 
constraint. (cf Grandma's I remarquable I soap 
or savon I remarkable I de grand-maman.) 
In one important case, however, equivalence 
always holds. Monolingual grammars have 
binary constituent-subconstituent structure if 
there are at most two symbols on the right-hand 
side of every rule. Then the following holds: 
Theorem 5 Given a well-formed code-switched 
sentence where the monolingual grammars have 
binary constituent-subconstituent structure. If 
two sister subconstituents are labeled A and B, 
respectively, the code-switch between them satis- 
ties the equivalence constraint. 
As we have seen, however, the theorem may not 
hold if rules may have more than two terms 
on their right-hand sides. The counter-example 
shown above, for example, represents the inser- 
tion of a language B subconstituent into an oth- 
erwise language A constituent. This requires 
two code-switches, one before and one after the 
inserted subconstituent. If a code-mixing strat- 
egy were to be based on the insertion of con- 
stituents in this way, every code-switch before 
an insertion would require the speaker to plan 
for an appropriate second code-switch later on 
in the sentence. 
While many types of relatively complex for- 
ward planning must be incorporated into mono- 
lingual production models, the distribution of 
code-switches in bilingual corpora is more con- 
sistent with a hypothesis of the independence of 
successive code-switches: no forced switches (or 
no planning). Where a switch takes place in be- 
tween two constituents, well-formedness of the 
code-switched sentence cannot depend further 
switches later on in the left-to-right order 7. 
Theorem 6 Given a well-formed code-switched 
sentence. If two sister subeonstituents are la- 
beled A and B, respectively, and there is no la- 
beled subconstituent between them, then under 
no forced switches, there must be a code-switch 
satisfying the equivalence constraint in the in- 
terval between the labeled subconstituents. 
2 Relaxing the constraints. 
2.1 Repetition-translation. 
The model in Section 1 precludes forms such 
as *se lavent \[ themselves where correspond- 
ing items from both virtual sentences (in this 
case se and themselves) appear. Such repeat- 
translations (also called portmanteau or palin- 
dromic constructions do occur, albeit rarely, in 
some corpora. 
Example (9) is drawn from the Finnish- 
English code-mixing corpus of Poplack et al. 
(1987b). We assume, following these authors' 
arguments, that this sentence consists of three 
fragments, with code-switches immediately be- 
fore and after the English preposition to. The 
rThere are some exceptions: these will be discussed 
in Section 2.2. 
15 
ellative case-marked kidneyst~i and illative aor- 
taan are formed of borrowings from English and 
behave as native items (e.g. there is no En- 
glish determiner preceding them as would be 
expected within English fragments; rather they 
manifest null determiners and case-marking 
characteristic of Finnish -- see Section 3). 
(9) Mutta se oli kidneyst~i I to \[ aortaan. 
but it was kidney-el, aorta-il. 
'But it was from the kidney to the aorta.' 
The interesting aspect of this example is that to 
and the ellative marker -an play identical roles 
and only one should have appeared in the ad- 
positional phrase containing aorta according to 
our model. The same, highly bilingual, speaker 
produced a similar example in (10). 
(10) Ja sitten, uh, miss~i h/in n- \[ at \[ yliopistossa 
and then where she n- university-in. 
otti, niin kuin, \[ art history. 
took-3p., like, 
'And then, uh, where did she- at university 
she took, like, art history.' 
Again, the inessive marker -ssa has the same 
function as the English preposition at and only 
one of them should have appeared, according to 
our model. 
This type of construction, involving the re- 
dundant use of functionally identical words, is 
rare -- examples (9) and (10) are the only two 
in the Finnish-English corpus -- and, as can 
be seen in (10), tends to evidence production- 
level difficulties (hesitations, autocorrection, 
etc.). Nishimura (1986) presents several simi- 
lar examples involving adpositional phrases for 
Japanese-English code-mixing. 
It is also possible to find occasional instances 
of redundant verb use in SVO/SOV mixing -- 
producing a SVOV structure. Examples (11) 
and (12) below are drawn from the Tamil- 
English code-mixing corpus of Sankoff et al. 
(1990). 
(11) They gave me a research 
grant \[ kodutaa. 
gave-3p.-pl.-past 
'They gave me a research grant.' 
(12) I was talking to I 
oru orutanooda peesindu iruntein. 
one person-com, talk-cont, be-lp.-sg.-past 
'I was talking to a person.' 
Still other examples from the same corpus com- 
bine redundant verb plus complementizer for 
propositional complements: 
(13) I think it's the European 
influence I nu ninaikirein. 
that think-lp.-sg.-pres. 
'I think that its the European influence.' 
Precisely how does this violate the conditions 
of our model, and can they be relaxed to ac- 
commodate it? Clearly the first postulate vio- 
lated (Section 1.5) is that the "...code-switched 
sentence is produced by taking part of one of 
\[the virtual sentences\], followed by part of the 
other, and so on, without using any word (or 
its translation) more than once, until every lex- 
ical element (or its translation) has been used 
up." What if we changed the latter part of this 
to "... and so on, until every lexical element 
(and/or its translation) has been used once?" 
This general extension allows for the use of any 
element as well as its translation in the same 
sentence. More limited extensions, where only 
specified lexical classes may occur in both lan- 
guages, would be more consistent with actual 
speech behaviour. 
With these kinds of changes, there is no dif- 
ficulty in retaining the left-to-right and nested 
first assumptions, as well as consituent label- 
ing criteria (i) and (ii). Condition (iii), formu- 
lated as it is in terms of the rank order of con- 
stituents, must be worded differently to capture 
the basic idea that a constituent is labeled ac- 
cording to language A whenever it is out place 
according to a rule of language B, and vice- 
versa. "Out of place" can no longer be detected 
by simply checking the rank order, but by ascer- 
taining whether any sister constituent preced- 
ing the candidate constituent is prohibited from 
preceding it by the appropriate rule of language 
B, and similarly for constituents following the 
candidate constituent. An analogous procedure 
can be used to verify the equivalence constraint. 
Typically, one sister constituent of the re- 
peated translated constituents will receive two 
conflicting labelings from criterion (iii) in this 
situation. The noun in the Finnish adpositional 
16 
phrase, the object in SVOV constructions, the 
proposition complement of both the English and 
Tamil verbs, all receive two labels this way. To 
weaken the model in order to accept such sen- 
tences, we must discard conflicting criterion (iii) 
labelings due to "out of place" configurations 
with respect to the repeated translated con- 
stituent. Criteria (i) and (ii) still operate. The 
equivalence constraint will not hold with respect 
to this sister constituent, but can be verified 
elsewhere. 
2.2 Insertional code-switching. 
In some bilingual communities, the code-mixing 
mode of discourse may include the possibility of 
inserting one specific type of constituent into 
positions where it would not occur monolin- 
gually. In the Tamil-English corpus in Section 
2.1, examples (14) and (15), as well as (13), il- 
lustrate the placement of an English proposition 
preceding the Tamil propositional complemen- 
tizer, instead of in its obligatory English posi- 
tion following that. 
(14) Even there, I am really lucky \[ nu collanum. 
that say must 
'Even there, one must say that I am really 
lucky.' 
(15) It corrodes your confidence I 
nu, enakku oru feeling s 
that I-dat. a 
'I have a feeling that it corrodes your 
confidence.' 
It is important to note that in this commu- 
nity this pattern is confined to the very par- 
ticular category of propositional complements. 
All other code-switches satisfy the equivalence 
constraint; none of the numerous other word- 
order conflicts between Tamil and English give 
rise to an insertional code-switching possibility. 
A different type of constituent insertion 
has been characterized quantitatively by Na'it 
M'Barek & Sankoff (1988). This involves the 
insertion, by bilingual Moroccans, of a full 
French noun phrase, including determiners and 
quantifiers, in all contexts where an Arabic 
noun phrase would be appropriate. This in- 
cludes, among other contexts, post-verbal sub- 
jects as in (16), which are not possible in French. 
s feeling is treated as a loanword, for reasons discussed 
in Section 3. 
Determiner-initial French noun phrases also ap- 
pear after demonstratives as in (17) and (18), 
producing demonstrative-determiner sequences, 
and after the indefinite wa.hd as in (18), produc- 
ing determiner-determiner sequences, neither of 
which is a French pattern. 
(16) 7aw \[les demandes 
arrived the applications 
'The applications arrived.' 
(17) migi b.hal duk \[ les avions 14gers 
This is not like these the airplanes light 
'It's not like these light planes.' 
17 
(18) ~a s'adresse surtout \[ l'wa.hd \[une 
this is targeted mostly at one a 
certaine classe \[ .hant walla \[le luxe\[ 
certain class because has become luxury 
bezzaf f' \[ les h6tels. 
much in the hotels 
'This is targeted mostly at a certain class 
because the hotels have become too 
luxurious.' 
The sentences we have shown containing ex- 
amples of constituent insertion are all excluded 
from the model based on the equivalence con- 
straint. For example, the English propositional 
complement preceding the Tamil complemen- 
tizer nu would be labeled for Tamil by crite- 
rion (iii) because of its non-English position, 
but this would conflict with the English label 
it would receive from criterion (ii) since it is 
a normal English sentence containing only En- 
glish lexical items. Similarly, the post-verbal 
subject consisting entirely of a normal French 
noun phrase receives conflicting labels from its 
position corresponding to Arabic rules and from 
its own constituent elements. 
It must be stressed that not all bilingual com- 
munities that develop code-mixing modes of dis- 
course make use of constituent insertion; those 
that do (e.g. Tamil-English or Arabic-French), 
use it very sparingly in the sense that typically 
only one type of constituent (English proposi- 
tions or French noun phrases) may be inserted 
in contexts (before nu, postverbally) where it 
would not be found in monolingual discourse. 
It is not difficult in this case to relax the 
model conditions so that such sentences are per- 
mitted. As in Section 2.1, the specified category 
is simply allowed to escape labeling by crite- 
rion (iii), and can be labeled by its own sub- 
constituents (criterion (ii)). There is no dan- 
ger that this will result in anomalous labeling 
higher in the phrase structure, since a sister con- 
stituent (the Tamil complementizer, the Ara- 
bic verb) will already have the contrary label, 
and the constituent containing them is thus pre- 
vented from receiving a label by way of criterion 
(ii). Note, however, that only those insertions 
which are not in conflict with the fundamen- 
tal production conditions left-to-right and most 
nested can be considered well-formed. In addi- 
tion, the equivalence constraint, wherever the 
specified category is not one of the constituents 
directly involved, still holds. 
3 The borrowing process. 
The equivalence constraint formalized in Sec- 
tion 1.6.1 has been verified as a general ten- 
dency in several communities - Puerto Rican 
Spanish and English in New York (Poplack, 
1980), Finnish and English (Poplack et al., 
1987b), Tamil and English (Sankoff et al., 
1990), Wolof and French, and Fongbe and 
French (Meechan & Poplack, 1995; Poplack & 
Meechan, 1995), Igbo and English (Eze, 1997), 
and others. However, there are actually rela- 
tively few data on which it has been indepen- 
dently tested, since most of the voluminous lit- 
erature on code-switching, especially that on 
insertional switching, is based on data which 
represent, we would claim, lexical borrowing 
(e.g. Eliasson, 1991; Mahootian & Santorini, 
1994; Backus, 1996). While code-switching es- 
sentially involves the reconciliation of the word 
orders of both languages, only the word-order 
of the recipient language is pertinent to bor- 
rowing. Thus attempts to understand code- 
switching based on a mixture of borrowing and 
true switching data are likely to be misleading. 
In the model constructed above, the borrow- 
ing process is not relevant. Loanwords, includ- 
ing those are ad hoc, "nonce", or momentary, 
uses, are not excluded, but simply considered 
to be syntactically integrated, i.e. to behave as 
native lexical items with respect to word order. 
How can this working hypothesis be validated? 
In Sections 3.1 and 3.2, we demonstrate an an- 
swer to this problem. 
3.1 Properties of loanwords. 
Many loanwords have long histories in the re- 
cipient language, are used by monolinguals (of- 
ten with no consciousness of their foreign et- 
ymology), are widespread and are accepted by 
m0nolingual dictionaries and other linguistic ar- 
biters. None of these non-structural character- 
istics, however, are necessary to the borrowing 
process. In many communities, bilinguals have 
access to essentially the entire content-word lex- 
icon of one language as potential loanwords 
into the other, perhaps for a single usage only. 
What is important is that when these words are 
borrowed the structural linguistic characteris- 
tics of their usage are the same as with estab- 
lished loanwords. What are these characteris- 
tics? Some of them are: integration into the 
recipient language at the syntactic, morpholog- 
ical, semantic and phonological levels, use as 
a single item independent of other donor lan- 
guage material, and restriction to nouns, verbs, 
adjectives, etc., to the exclusion of determiners, 
pronouns, prepositions and other grammatical 
words. 
Often, during the study of a bilingual cor- 
pus, we discover a pattern of words from a spe- 
cific lexical category in language A appearing 
in mixed discourse in contexts where they seem 
to violate the equivalence constraint, but when 
considered as language B words, i.e. borrow- 
ings, there is no violation, e.g. kidney in (9), 
feeling in (15). Thus these words seem syntac- 
tically integrated into language B. To confirm 
their borrowed status, we verify the other prop- 
erties of loanwords. 
Phonological integration turns out to be an 
unreliable indicator, for two reasons (cf Poplack 
et al., 1987a). One is that bilinguals, in con- 
trast to monolinguals, tend to be aware of the 
etymology of loanwords and, in some commu- 
nities, will often reflect this knowledge in their 
pronunciation of borrowed items. Second, in 
some communities, the learning context results 
in phonologies for languages A and B which 
converge in unpredictable and diverse ways from 
speaker to speaker. 
Semantic integration refers to a shift in func- 
tion or meaning of a loanword from donor lan- 
guage characteristics to recipient language char- 
acteristics. This may often be documented for 
established loanwords that have had time to 
18 
evolve within the host language, or for borrow- 
ings between languages whose functional cate- 
gories are structured very differently, but in gen- 
eral, where bilingual borrowings are most fre- 
quently from and into the category of nouns, the 
criterion of semantic integration, though satis- 
fied, may not always revealing. 
The criterion of isolated occurrence of loan- 
words in recipient language contexts is more 
universal and is usually relatively easy to ap- 
ply. The main difficulties come from compound 
words and other multi-word forms whose status 
as single lexical items is not always clear. Sta- 
tistically, these should not constitute a major 
problem. There is also the possibility of coin- 
cidence. If nouns are often borrowed and ad- 
jectives are often borrowed, then occasionally a 
noun-adjective combination will appear to have 
been borrowed together, when this is just the 
result of chance. This will also be relatively 
rare. 
The lexical/grammatical (or content/ func- 
tion) contrast is also useful. It is true that 
among the world's languages, loanwords have on 
occasion included prepositions, pronouns, de- 
terminers, and other grammatical categories, 
but these are exceptional, and the overwhelming 
tendency is for borrowing, and especially one- 
time borrowing by bilinguals, to affect nouns, 
and to a lesser extent, verbs, adjectives and ad- 
verbs. Moreover, in specific communities, bilin- 
gual borrowing may be focused on particular 
categories more than in other communities, and 
these patterns may be useful for analytical pur- 
poses. 
Finally, it is the criterion of morphological in- 
tegration which is of great interest. Loanwords, 
established or momentary, are inflected exclu- 
sively through recipient language morphological 
rules. Insofar as such marking is non-null and is 
different for language A and language B, words 
borrowed from the former into the latter should 
display exclusively language B inflectional mor- 
phology. 
3.2 Case marking of English-origin 
nouns in Tamil 
In the Tamil corpus referred to in Sections 2.1 
and 2.2, many English-origin nouns occur in 
preverbal position, where the verb is an in- 
flected Tamil form. Tamil being a SOV lan- 
guage, this is just where Tamil direct (and indi- 
marker marker 
present absent N 
ACCUSATIVE 
English origin 29% 71% 108 
Native Tamil 
(no pronouns) 39% 61% 51 
DATIVE 
English origin 86% 14% 91 
Native Tamil 99% 1% 230 
Table 1: Variable accusative and dative marking 
on English-origin and native Tamil objects. 
rect) objects appear. Examining these English- 
origin nouns, we first note that these occur most 
frequently in isolation, and occasionally as com- 
pounds, or as familiar adjective-noun combina- 
tions, but never preceded by English preposi- 
tions, articles, quantifiers or demonstratives as 
would frequently be the case if these were parts 
of well-formed English fragments resulting from 
code-switching. 
Second, whereas the preponderance of prever- 
bal native Tamil objects are actually pronouns, 
from 45-70% depending on the case, no English 
pronouns whatsoever appear in this context, as 
would be expected from borrowings, but not if 
these were code-switches into English fragments 
-- which would normally include at least the oc- 
casional pronoun. 
Third, it is the inflectional morphology on 
these nouns which is the most revealing. They 
either have null morphology or Tamil inflec- 
tions. Since in Tamil the numerically fre- 
quent accusatives and datives are prescribed to 
take non-null case-marking, we examine mark- 
ing rates quantitatively. In fact, as in Table 
1, many (non-pronominal) Tamil forms are un- 
marked, especially accusatives. The Engiish- 
origin forms show remarkably parallel rates, es- 
pecially when the accusative-dative contrast is 
considered. This morphological integration into 
Tamil is exactly what would be expected of bor- 
rowings, and certainly not of well-formed En- 
glish fragments produced by code-switching. 
In summary, the criteria of syntactic integra- 
tion, isolation, lexical category, and morpholog- 
ical integration all confirm the loanword status 
of the preverbal English-origin nouns, and jus- 
tify our considering them as Tamil nouns for 
the purposes of applying our model of code- 
19 
switching. 
3.3 Formal considerations 
Formally, the only adaptation of our model nec- 
essary to allow for borrowing is, for specified 
terminal categories in T, the list of words in 
language A in the category is added in to the 
pre-existing list for language B, so that there 
are now two possible translations in B for each 
word in A in this category. The uniqueness 
statement in Theorem 1 has to be modified to 
take this into account, but this leads to no diffi- 
culty. We presume of course that the borrowed 
word in B can be distinguished from its "ety- 
mological" origin in A by the tests and criteria 
illustrated in Section 3.2. 
Discussion. 
The core of this work is our model of 
equivalence-point code-switching. This avoids 
issues of grammatical theory by focusing on 
the "real-time" production of a code-mixed sen- 
tence drawing on the output of two monolingual 
grammars. 
Our model is built on an earlier formulation of 
the equivalence constraint (Sankoff & Mainville, 
1986). It is the production aspect here, how- 
ever, that allows us to achieve the all-important 
well-formedness of monolingual fragments, not 
strictly guaranteed in the earlier work, and to 
model the essential unpredictability of code- 
switching. The present version (Sankoff, 1998) 
has a more economical protocol for constituent 
labeling and a more complete account of the co- 
incidence (or lack thereof) between word-level 
switching and constituent-level switching. We 
have shown here how to weaken the strong con- 
ditions leading to Theorems 5 and 6 to account 
for other types of code-switching that have been 
reported. 
We have allowed some degree of asymmetry 
in the model. Borrowing can be unidirectional 
with respect to specific categories. The same 
is true for constituent insertion. Further de- 
velopment will require weakening the one-to- 
one correspondence of the sets of rules, and of 
the grammatical and lexical categories of the 
two languages. For example, the use of spe- 
cialized incorporation devices, like inflection- 
carrying dummy verbs, or techniques for mark- 
ing borrowed adverbs, typically belong to one 
language and not the other. 
We have not treated the topic of interference 
in this presentation. Interference differs from 
borrowing in several respects, in particular on 
the level of intentionality -- interference is more 
likely to be avoided or corrected by speakers, 
and is more likely to show up in communities 
where the domain of monolingualism, and fre- 
quency of use of the affected language are re- 
stricted. Nevertheless, interference has interest- 
ing consequences for our model in that it tends 
to affect pre-sentential discourse markers, tags, 
conjunctions, prepositions and other grammat- 
ical morphemes rather than lexical items as is 
the case for loanwords. Both borrowing and in- 
terference can lead to the long-term establish- 
ment of lexical items, so that when interference 
is frequent, the distinction between the two be- 
comes of interest. 
Acknowledgements 
This work supported in part by grants from 
the Natural Sciences and Engineering Research 
Council and the Social Sciences and Humanities 
Research Council. The author is a Fellow of the 
Canadian Institute for Advanced Research. 

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