Consonant Spreading in Arabic Stems 
Kenneth R. BEESLEY 
Xerox Research Centre Europe 
Grenoble Laboratory 
6, chemin de Maupertuis 
38240 MEYLAN 
France 
Ken. Beesley@xrce. xerox, com 
Abstract 
This paper examines the phenomenon of conso- 
nant spreading in Arabic stems. Each spread- 
ing involves a local surface copying of an un- 
derlying consonant, and, in certain phonologi- 
cal contexts, spreading alternates productively 
with consonant lengthening (or gemination). 
The morphophonemic triggers of spreading lie 
in the patterns or even in the roots themselves, 
and the combination of a spreading root and 
a spreading pattern causes a consonant to be 
copied multiple times. The interdigitation of 
Arabic stems and the realization of consonant 
spreading are formalized using finite-state mor- 
photactics and variation rules, and this ap- 
proach has been successfully implemented in a 
large-scale Arabic morphological analyzer which 
is available for testing on the Internet. 
1 Introduction 
Most formal analyses of Semitic languages, in- 
cluding Arabic, defend the reality of abstract, 
unpronounceable morphemes called ROOTS, 
consisting usually of three, but sometimes two 
or four. consonants called RADICALS. The clas- 
sic examples include ktb (~. ,D ~)1, appearing 
in a number of words having to do with writ- 
ing, books, schools, etc.; and drs (~9 z), ap- 
pearing in words having to do with studying, 
learning, teaching, etc. Roots combine non- 
concatenatively with PATTERNS to form STEMS, 
a process known informally as INTERDIGITA- 
TION or INTERCALATION. We shall look first 
at Arabic stems in general before examining 
GEMINATION and SPREADING, related phenom- 
ena wherein a single underlying radical is real- 
~The Arabic-script examples in this paper were pro- 
duced using the ArabTeX package for TEX and DTEX by 
Prof. Dr. Klaus Lagally of the University of Stuttgart. 
daras 
duris 
darn'as 
duruus 
diraasa(t) 
darraas 
madrasa(t) 
madaaris 
madrasiyy 
tadriis 
'study' 
'be studied' 
'teach' 
'lessons' 
'study' 
'eager student' 
'school' 
'schools' 
'scholastic' 
'instruction' 
verb 
verb 
verb 
noun 
noun 
noun 
noun 
noun 
adj-like 
noun 
Figure 1: Some stems built on root drs 
ized multiple times in a surface string. Semitic 
morphology, including stem interdigitation and 
spreading, is adequately and elegantly formaliz- 
able using finite-state rules and operations. 
1.1 Arabic Stems 
The stems in Figure 12 share the drs root mor- 
pheme, and indeed they are traditionally or- 
ganized under a drs heading in printed lexi- 
cons like the authoritative Dictionary of Mod- 
ern Written Arabic of Hans Wehr (1979). 
A root morpheme like drs interdigitates with 
a pattern morpheme, or, in some analyses. 
with a pattern and a separate vocalization mor- 
pheme, to form abstract stems. Because inter- 
digitation involves pattern elements being in- 
serted between the radicals of the root mor- 
pheme, Semitic stem formation is a classic 
example of non-concatenative morphotactics. 
Separating and identifying the component mor- 
phemes of words is of course the core task of 
morphological analysis for any language, and 
analyzing Semitic stems is a classic challenge 
2The taa~ marbuu.ta, notated here as (t), is the fem- 
inine ending pronounced only in certain environments. 
Long consonants and long vowels are indicated here with 
gemination. 
117 
for any morphological analyzer. 
1.2 Interdigitation as Intersection 
Finite-state morphology is based on the 
claim that both morphotactics and phonologi- 
cal/orthographical variation rules, i.e. the rela- 
tion of underlying forms to surface forms, can 
be formalized using finite-state automata (Ka- 
plan and Kay, 1981; Karttunen, 1991; Kaplan 
and Kay, 1994). Although the most acces- 
sible computer implementations (Koskenniemi, 
1983; Antworth, 1990; Karttunen, 1993)of 
finite-state morphotactics have been limited to 
building words via the concatenation of mor- 
phemes, the theory itself does not have this limi- 
tation. In Semitic morphotactics, root and pat- 
tern morphemes (and, according to one's the- 
ory, perhaps separate vocalization morphemes) 
are naturally formalized as regular languages, 
and stems are formed by the intersection, rather 
than the concatenation, of these regular lan- 
guages. Such analyses have been laid out else- 
where (Kataja and Koskenniemi, 1988; Beesley, 
1998a; Beesley, 1998b) and cannot be repeated 
here. For present purposes, it will suffice to view 
morphophonemic (underlying) stems as being 
formed from the intersection of a root and a pat- 
tern, where patterns contain vowels and C slots 
into which root radicals are, intuitively speak- 
ing, "plugged", as in the following Form I per- 
~ct active and passive verb examples. 
Root: d r s k t b q t i 
Pattern: CaCaC CaCaC CaCaC 
Stem: daras katab qatal 
Root: d r s k t b q t 1 
Pattern : CuCiC CuCiC CuCiC 
Stem: duris kutib qutil 
Prefixes and suffixes concatenate onto the stems 
in the usual way to form complete, but still mor- 
phophonemic, words; and finite-state variation 
rules are then applied to map the morphophone- 
mic strings into strings of surface phonemes or 
orthographicM characters. For an overview of 
this approach, see Karttunen, Kaplan and Zae- 
hen (1992). 
Following Harris (1941) and Hudson (1986), 
and unlike McCarthy (1981), we also allow the 
patterns to contain non-radical consonants as 
in the following perfect active Form VII, Form 
VIII and Form X examples. 
Form VII Form VIII Form X 
Root: k t b k t b kt b 
Pattern: nCaCaC CtaCaC staCCaC 
Stem : nkat ab ktatab staktab 
In this formalization, noun patterns work ex- 
actly like verb patterns, as in the following ex- 
amples: 
Root: k t b k t b kt b 
Pattern: CiCaaC CuCuC maCCuuC 
Stem: kitaab kutub maktuub 
Gloss : "book" "books" "letter" 
Where such straightforward intersection of 
roots and patterns into stems would appear to 
break down is in cases of gemination and spread- 
ing, where a single root radical appears multiple 
times in a surface stem. 
2 Arabic Consonant Gemination and 
Spreading 
2.1 Gemination in Forms II and V 
Some verb and noun stems exhibit a double re- 
alization (a copying) of an underlying radical, 
resulting in gemination 3 or spreading at the sur- 
face level. Looking at gemination first, it is best 
known from verb stems known in the European 
tradition as Forms II and V, where the middle 
radical is doubled. Kay's (1987) pattern nota- 
tion uses a G symbol before the C slot that 
needs to be doubled. 4 
3Gemination in Arabic words can alternatively be an- 
alyzed as consonant lengthening, as in Harris (1941) and 
as implied by Holes (1995). This solution is very attrac- 
tive if the goal is to generate fully-voweled orthograph- 
ical surface strings of Arabic, but for the phonological 
examples in this paper we adopt the gemination repre- 
sentation as used by phonologists like McCarthy (1981). 
4 Kay's stem-building mechanism, using a multi-tape 
transducer implemented in Prolog, sees G on the pattern 
tape and writes a copy of the middle radical on the stem 
tape without consuming it. Then the following C does 
the same but consumes the radical symbol in the usual 
way. Kay's analysis in fact abstracts out the vocaliza- 
118 
Root: k t b d r s 
Pattern: CaGCaC CaGCaC 
Stem: kattab darras 
In the same spirit, but with a different mecha- 
nism, our Form II and Form V patterns contain 
an X symbol that appears after the consonant 
slot to be copied. 
Root: k t b d r s 
Pattern: CaCXaC CaCXaC 
Stem: katXab darXas 
As in all cases, the stem is formed by straight- 
forward intersection, resulting in abstract stems 
like darXas. The X symbol is subsequently re- 
alized via finite-state variation rules as a copy of 
the preceding consonant in a phonological gram- 
mar (/darras/) or, in an orthographical system 
such as ours, as an optionally written shadda di- 
acritic (~r,~.~). Finite-state rules to effect such 
limited local copying are trivially written, s 
2.2 Gemination/Spreading in Form IX 
Spreading, which appears to involve consonant 
copying over intervening phonemes, is not so 
different from gemination; and indeed it is com- 
mon in "spreading" verb stems for the spread- 
ing to alternate productively with gemination. 
The best known example of Arabic consonant 
spreading is the verbal stem known as Form 
IX (the same behavior is also seen in Form 
XI, Form XIV, Form QIV and in several noun 
forms). A typical example is the root dhm 
(~, 0 z), which in Form IX has the meaning "be- 
come black". 
Spreading is not terribly common in Modern 
Standard Arabic, but it occurs in enough verb 
and noun forms to deserve, in our opinion, full 
treatment. In our lexicon of about 4930 roots, 
tion, placing it on a separate transducer tape, but this 
difference is not important here. For extensions of this 
multi-tape approach see Kiraz (1994; 1996). The cur- 
rent approach differs from the multi-tape approaches in 
formalizing roots, patterns and vocalizations as regular 
languages and by computing ("linearizing") the stems 
at compile time via intersection of these regular lan- 
guages (Beesley, 1998a; Beesley, 1998b). 
5See, for example, the rules of Antworth (1990) for 
handling the limited reduplication seen in Tagalog. 
by d & .~ ,4. 
hmr -J i* C 
hwl ~ 3 C 
dhm ~, 0 .~ 
rbd ~ ~. 3 
rfd. 0~, ~..)~ 
zrq ~ .~ .3 
zwr .~ .~ .) 
smr .~ ~. 
swd ~ .~ 
J'qr .9 ~ j 
J'mt. 3, j 
s.fr .~ J u" 
s.hb ~. o o" 
"C 
~gbr A '-?. t 
qtm i* ,D 
kmd ~ ~. 2 
'become white' 
'turn red' 'blush' 
'be cross-eyed' 'squint' 
'become green' 
'be moist' 
'become black' 
'become ashen' 'glower' 
'drip' 'scatter' 'break up' 
'be blue in color' 
'alienate' 
'become brown' 
'become black' 
'be of fair complexion' 
'turn gray' 
'turn yellow/pale' 
'become reddish' 
'be crooked' 'be bent' 
'be dust-colored' 
'be dark-colored' 
'become smutty/dark' 
Figure 2: Roots that combine with Form IX 
patterns 
20 have Form IX possibilities (see Figure 2). 
Most of them (but not all) share the general 
meaning of being or becoming a certain color. 
McCarthy (1981) and others (Kay, 1987; Ki- 
raz, 1994; Bird and Blackburn, 1991) postulate 
an underlying Form IX stem for dhm that looks 
like dhamam, with a spreading of the final m 
radical; other writers like Beeston (1968) list the 
stem as dhamm, with a geminated or length- 
ened final radical. In fact, both forms do oc- 
cur in full surface words as shown in Figure 3, 
and the difference is productively and straight- 
forwardly phonological. For perfect endings like 
+a ('he') and +at ('she'), the final consonant is 
geminated (or "lengthened", depending on your 
formal point of view). If, however, the suffix be- 
gins with a consonant, as in +tu (T) or +ta 
('you, masc. sg.'), then the separated or true 
spreading occurs. 
From a phonological view, and reflecting the 
119 
dhamm+a ~.~.~\] 'he turned black' 
dhaniam+tu -~2~.~! 'I turned black' 
Figure 3: Form IX Gemination vs. Spreading 
notation of Beeston, it is tempting to formal- 
ize the underlying Form IX perfect active pat- 
tern as CCaCX so that it intersects with root 
dhm to form dhamX. When followed by a suf- 
fix beginning with a vowel such as +a or +at, 
phonologically oriented variation rules would re- 
alize the X as a copy of the preceding consonant (/dhamm/). 
Arabic abhors consonant clus- 
ters, and it resorts to various "cluster busting" 
techniques to eliminate them. The final phono- 
logical realization would include an epentheti- 
cal/?i/on the front, to break up the dh clus- 
ter, and would treat the copied m as the on- 
set of a syUable that includes the suffix: /?id- 
ham-rna/, or, orthographically, ~.2b.~!. When 
followed by a suffix beginning with a conso- 
nant, as in dhamX+tu, the three-consonant 
cluster would need to be broken up by another 
epenthetic vowel as in /?id-ha-rnam-tu/, or, 
orthographically, "~.~!. However, for reasons 
to become clearer below when we look at bilit- 
eral roots, we defined an underlying Form IX 
perfect active pattern CCaCaX leading to ab- 
stract stems like dhamaX. 
2.3 Other Cases of Final Radical 
Gemination/Spreading 
Other verb forms where the final radical is 
copied include the rare Forms XI and XIV. Root 
lhj (.~ ~ ~) intersects with the Form XI perfect 
active pattern CCaaCaX to form the abstract 
stem lhaajaX ("curdle"/"coagulate"), leading 
to surface forms like /?il-haaj-ja/ (.~5~!) and 
/?il-haa-jaj-tu/ (-,~.~!) that vary exactly 
as in Form IX. The same holds for root shb 
(,.?. ~ ~,,), which takes both Form IX (s.habaX) 
and Form XI (shaabaX), both meaning "be- 
come reddish". In our lexicon, one root q% 
(~r' ~. d) takes form XIV, with patterns like the 
perfect active CCanCaX and imperfect active 
CCanCiX ("be pigeon-breasted"). Other sim- 
ilar Form XIV examples probably exist but are 
not reflected in the current dictionary. 
Aside from the verbal nouns and partici- 
ples of Forms IX, XI and XIV, other noun-like 
patterns also involve the spreading of the fi- 
nal radical. These include CiCCiiX and Ca- 
CaaCiiX, taken by roots nhr (.; ~ ~3), mean- 
ing "skilled/experienced", and r~d (~ \[_~) 
meaning "coward/cowardly". The CaCaaCiiX 
pattern also serves as the broken (i.e. ir- 
regular) plural for CuCCuuX stems for the 
roots z~r (.~ ~5) meaning "ill-tempered", shr 
(.J ~ 0") meaning "thrush/blackbird", 1yd 
(~ ~_ J) meaning "chin", and thr (.~ ~ .~) and 
t.xr (.j ~ .b), both meaning "cloud". When an 
X appears after a long vowel as in t.uxruuX, 
it is always realized as a full copy of the pre- 
vious consonant as in /tuxruur/ (_;.%~9d,), 1lo 
matter what follows. 
2.4 Middle Radical 
Gemination/Spreading 
Just as Forms II and V involve gemination of the 
middle radical, other forms including Form XII 
involve the separated spreading of the middle 
radical. A preceding diphthong, like a preceding 
long vowel, causes X to be realized as a full 
copy of the preceding consonant, as shown in 
the following examples. 
Root: 
Pattern: 
Stem: 
Surface: 
Form: 
Gloss: 
hd b 
CCawXaC 
hdawXab 
hdawdab 
Form XII perfect active 
"be vaulted" "be embossed" 
~OOt: X~ n 
Pattern: CCawXiC 
Stem: xfawXin 
Surface: xfaw~in 
Form: Form XII imperfect active 
Gloss: "be rough" 
Root: 
Pattern: 
Stem: 
Surface: 
Form: 
Gloss: 
xd b 
muCCawXiC 
muxdawXib 
muxdawdib 
Form XII active participle 
"become green" 
120 
tamm+a tamam-t-tu 
$" • o." 
Figure 4: Biliteral Form I Stems 
Root: xd r 
Pattern: CCiiXaaC 
Stem: xdiiXaar 
Surface: xdiidaar 
Form: Form XII verbal noun 
Gloss: "become green" 
A number of nouns have broken plurals that also 
involve spreading of the middle radical, con- 
trasting with gemination in the singular. 
x f f "bat" 
$• 
xufXaaf ~u4. 
singular gemination 
x f f "bats" plural spreading 
xafaaXiif ¢.2:~/2~.A" " : : 
d b r "hornet" 
dabXuur _)~. 
singular gemination 
d b r "hornets" plural spreading 
dabaaXiir .~.~U3 
A few other patterns show the same behavior. 
While not especially common, there are more 
roots that take middle-radical-spreading noun 
patterns than take the better-known Form IX 
verb patterns. 
3 Biliteral Roots 
As pointed out ill McCarthy (1981, p. 396- 
7), the gemination vs. spreading behavior of 
Form IX stems is closely paralleled by Form 
I stems involving traditionally analyzed "bilit- 
eral" or ':geminating" roots such as tm (also 
characterized as tmm) and sm (possibly smm) 
and many others of the same ilk. As shown in 
Figure 4, these roots show Form I gemination 
with suffixes beginning with a vowel vs. full 
spreading when the suffix begins with a conso- 
nant. However Form IX is handled, these par- 
allels strongly suggest that the exact same un- 
derlying forms and variations rules should also 
handle the form I of biliteral roots. 
However, the Form I perfect active pattern, 
in the current notation, is simply CaCaC (or 
Root: k t b k t b 
Pattern: CaCaC CaCaC 
Lexicah katab+a katab+tu 
Surface: katab a katab tu 
Orthography: "3 
Figure 5: Ordinary Form I behavior 
Root: t m X t m X 
Pattern: CaCaC CaCaC 
Lexical: tamaX+a tamaX+tu 
Surface: tamma tamamtu 
• O~" Orthography: 5/ 
Figure 6: Biliteral tm formalized as tmX 
idiosyncratically for some roots, CaCuC or 
CaCiC). As shown in Figure 5, there is no ev- 
idence, for normal triliteral roots like ktb, that 
any kind of copying is specified by the Form I 
pattern itself. 
Keeping CaCaC as the Form I perfect active 
pattern, the behavior of biliteral roots falls out 
effortlessly if they are formalized not as srn and 
tin, nor as smm and tram, but as smX and 
tmX, with the copying-trigger X as the third 
radical of the root itself. Such roots intersect 
in the normM way with triliteral patterns as in 
Figure 6, and they are mapped to appropriate 
surface strings using the same rules that realize 
Form IX stems. 
4 Rules 
The TWOLC rule (Karttunen and Beesley, 1992) 
that maps an X, coming either fl'om roots like 
tmX or from patterns like Form IX CCaCaX. 
into a copy of the previous consonant is the fol- 
lowing, where Cons is a grammar-level variable 
ranging freely over consonants, LongVowel is a 
grammar-level variable ranging freely over long 
vowels and diphthongs, and C is an indexed lo- 
cal variable ranging over the enumerated set of 
consonants. 
X:C <=> 
:C \:Cons+ _ ~+: Cons ; 
:C LongVowel _ ; 
:C X::_ ; 
where C in (b t 0 j h x d 6 r z sf d;6 xfqk 
imnhwy); 
121 
The rule, which in fact compiles into 27 rules, 
one for each enumerated consonant, realizes un- 
derlying X as surface C if and only if one of the 
following cases applies: 6 
* First Context: X is preceded by a sur- 
face C and one or more non-consonants, 
and is followed by a suffix beginning 
with a consonant. This context matches 
lexical dhamaX+tu, realizing X as m 
(ultimately written ",/~/,L~.~!), but not 
dhamaX+a, which is written ~.~!. 
- Second Context: X is preceded by a surface 
C and a long vowel or diphthong, no matter 
what follows. This maps lexical dabaaXiir 
to dabaabiir (.t U-%). 
• Third Context: X is preceded by a surface 
C, another X and any symbol, no matter 
what follows. This matches the second X 
in samXaX+tu and samXaXWa to pro- 
duce samXam+tu and samXam+a re- 
spectively, with ultimate orthographical re- 
alizations such as ~" and "~¢~. 
In the current system, where the goal is to 
recognize and generate orthographical words 
of Modern Standard Arabic, as represented in 
ISO8859-6, UNICODE or an equivalent encod- 
ing, the default or "elsewhere" case is for X to 
be realized optionally as a shadda diacritic. 
5 Multiple Copies of Radicals 
When a biliteral root like smX intersects with 
the Form II pattern CaCXaC, the abstract 
result is the stem samXaX. The radical m 
gets geminated (or lengthened) once and spread 
once to form surface phonological phonological 
strings like /sammama/ and /sammamtu/, 
which become orthographical -~ and "~ re- 
spectively. And if both roots and patterns can 
contain X, then the possibility exists that a 
copying root could combine with a copying pat- 
tern, requiring a full double spreading of a rad- 
ical in the surface string. This in fact happens 
in a single example (in the present lexicon) with 
~The full rule contains several other contexts and fine 
distinctions that do not bear on the data presented here. 
For example, the w in the set C of consonants must be 
distinguished from the w-like offglide of diphthongs. 
Root: m k X 
Pattern: CaCaaXiiC 
Abstract stem: makaaXiiX 
Surface: makaakiik 
Gloss: "shut tles" 
Figure 7: Double Consonant Spreading 
the root mkX, which combines legally with the 
noun pattern CaCaaXiiC as in Figure 7. In 
the surface string makaakiik ("shuttles"), or- 
thographically • A~, the middle radical k is 
spread twice. The variation rules handle this 
and the smX examples without difficulty. 
6 System Status 
The current morphological analyzer is based 
on dictionaries and rules licensed from an ear- 
lier project at ALPNET (Beesley, 1990), re- 
built completely using Xerox finite-state tech- 
nology (Beesley, 1996; Beesley, 1998a). The 
current dictionaries contain 4930 roots, each 
one hand-coded to indicate the subset of pat- 
terns with which it legally combines (Buck- 
walter, 1990). Roots and patterns are inter- 
sected (Beesley, 1998b) at compile time to yield 
90,000 stems. Various combinations of prefixes 
and suffixes, concatenated to the stems, yield 
over 72,000,000 abstract words. Sixty-six finite- 
state variation rules map these abstract strings 
into fully-voweled orthographical strings, and 
additional trivial rules are then applied to op- 
tionally delete short vowels and other diacritics, 
allowing the system to analyze unvoweled, par- 
tially voweled, and fully-voweled orthographical 
strings. 
The full system, including a Java interface 
that displays both input and output in Arabic 
script, is available for testing on the Internet 
at http ://www. xrce. xerox, com/research/ 
mltt/arabic/. 
122 

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