THE SPECIFICATION OF TIME MEANING FOR MACHINE TRANSLATION 
Frank van Eynde - Catholic University Leuven 
Blijde Inkomststraat, 21, 3000 Leuven, Belgium 
Louis des Tombe - Utrecht State University 
Trans I 14~ 3512 3K Utrecht, Holland 
Fons Maes - Catholic University of Tilburg 
Postbus g0153, 5000 LE Tilburg~ Holland 
In this paper, we put Torward some ideas on 
the reoresentation of time in a machine 
translation system. In such a system, we 
usually have the following four representations: 
- source text 
- source representation 
- target representation 
- target text 
In an interlingual system, there is no 
difference between source and target 
representation; in a transfer-based system, 
the step between the two is usually called 
transfer, and this step is meant to be as 
simple as possible. 
The research described was originally done in 
the framework of the EUROTRA MT project, 
which is transfer-based. However, it can 
be used in other MT systems as well; in 
Tact, it is very well suited for interlingual 
systems. 
The problem with time meaning is that it is 
expressed in natural languages in a way that 
is non-universal and, moreover, not very 
perspicuous prima facie. As a consequence, it 
is difficult to find rules for the 
translation of the tense form of the verb. 
In this paper, we propose a conceptual 
calculus in which the meanings of 
language specific temporal expressions 
can be represented in an interlingual way, 
so that the translation of the latter can 
be achieved via the corresponding conceptual 
representations. 
The exposition will consist of three parts. 
First, we define a time axis model, i.e. a 
model in which temporal concepts can be 
understood. 
Second, we establish two types of general 
constraints: 
~i) Constraints on possible time meaning 
representations, resulting in a restricted 
class of meanings for time anO related 
phenomena in terms of this model. 
(ii) Constraints on the relations between 
syntactic/morphological forms and time 
meanings, resulting in a non-arbitrary 
relation between form and meaning. 
Third, we show how the calculus can be 
used for the interlingual analysis of 
the tense forms of verbs. 
I. The time axis model. 
The model is a temporal structure 
<time,< >, where 
time is a set of elements called time-points; 
(ii) 
< is a binary relation that linearly orders 
time (and can be interpreted as 'precedes'); 
An interval (1) is a subset of time that does 
not contain 'gaps', i.e.: ~ tl,t2 E I 
t3 G time (t1<t3<t2 -> t3 E I ). 
We now turn to the time meanings anq their 
representations. 
First, we want to separate the expression 
that represents time meaning from the rest of 
the sentence. The instruments we use are 
based on Dowty (1979): 
(i) 
A tNo-place operator AT that takes an 
interval and a formula to yield another 
formula, with the following interpretation: 
W(AT(I~O)=I at whatever time t if÷ W(O)=I at 
the interval I. 
(ii~ 
Temporal predicates that take an interval to 
yield a formula, e.g., 
W(yesterday(1))=1 iff the interval I is a 
subset of yesterday. 
35 
(iii) 
Temporal relations that take two intervals 
to yield a formula, e.g., 
W(beforeil,J))=1 iff 
t,t' c time (t E I & t' s J ---> t<t') 
(iv) 
k-abstraction to separate the temporal 
expression from the basic proposition, so 
that the representation of the temporal 
expresssion takes the following form: 
(I) 
k p 3 I,, I=, ...S time (Rel,(Ij,l,) k ..° & 
Pred.(l.J & m.! & AT (I,, p) ) 
where the I, are intervals, the Relj are 
binary relations between intervals like 
:before , the Predw are predicates like 
yesterday ~, and p is a basic proposition, 
from which all time-relevant parts have 
been removed. 
The category of expression (I 
be applied to a basic proposi 
functional way. 
) is t/t; it can 
tion in a 
The interpretation of (I) is the set of 
propositions that are true at some given 
interval I,. This is similar to Kripke's 
definition of the notion of 'possible world': 
'A possible world is given by the descriptive 
conditions we associate with it .... ' (1972, 
p. 44). Analogously, a time interval 
can be identified with the collection of 
propositions that are true at it. 
2. A theory of time meanings. 
In many discussions of time meaning, a 
Oistinction is made between an internal and 
an external temporal system. The external 
system represents the temporal relation 
between the state of affairs as described by 
the basic proposition and the time at which 
the utterance takes place. This system always 
refers to the speaker or writer, and 
consequently it is a deictic system. The 
internal system is about such things as 
whether the state of affairs expressed in the 
basic proposition is described as going on, 
having lust started, having been completed, 
etc. This type of information is often called 
aspectual. 
In this paper, we adopt the following three 
basic principles for the representation of 
time meanings: 
(I) 
Each time meaning representation contains 
exactly three time intervals: 
- the time of speech or narration (S) 
- the time of event (E), i.e. the interval 
at which the basic proposition is said 
to be true 
- one time of reference (R) 
The S-interval consists of one point only: 
it is a singleton. The R- and E-intervals are 
non-empty subsets of time. 
(II) 
The deictic part of time meaning is represented 
by a binary relation between S and R and 
optionally by one predicate over R, 
(Ill) 
Aspect is represented by a binary relation 
between R and E, and optionally by one 
predicate over E. 
Principles (1), (II), and (Ill) together 
imply that the general form of a time meaning 
representation can be somewhat simplified. It 
will now be: 
(2) 
k p 3 S,R,E ~ time (Relt(R,S) & Pred.(R) & 
Rel=(E,R) & Pred=(E) & AT(E,p)) 
Apart from the constraints on possible 
time meaning representations there are some 
constraints on the relation between the 
time meanings and the language specific 
morphosyntactic forms for expressing those 
meanings: 
(IV) 
The predicates over R are those time 
adverbials that can be used as answers to 
when-questions, such as 
(3) yesterday, now, next week, on Tuesday 
(V) 
The predicates over E are (a.o.) the 
duration time adverbials, such as 
(4) for an hour, five weeks, since 
Christmas, until ~une 
(vI) 
The relations between R and S and between 
E and R are determined by the interaction 
of the verbal tense forms and the time 
adverbials in ways to be specified and 
exemplified in section three. 
We will now present the deictic and the 
aspectual components of the temporal system 
in some detail. 
2.1. The deictic system. 
As possible relations between S and R we 
will take 
(i) before (R,S), defined as in I. 
(ii) after (R,S), defined analogously 
(iii) contain (R,S), defined as follows : 
t s time (t ~ S ---> t ~ R) 
36 
The specifiers of the reference time are the 
when-adverbials. A classification of the 
latter that appears to be relevant for the 
assignment of deictic values in particular 
cases is the following one : 
in fact, an iterative interpretation, and for 
such interpretations we need a more complex 
representation format. This will not be 
developed in this paper, but see Van Eynde 
(forthcoming). 
deictic absolute 
before after contain on Tuesday 
yesterday n xt now 
week 
The deictic when-adverbials define the position 
of the reference time with respect to the time 
of speech, and cannot be combined with all 
possible tenses. An after-adverbial is, for 
instance, not compatible with the simple past: 
(5) * he came next week 
The absolute when-adverbials determine the 
position of the reference time independently 
from the speech time. Depending an which tense 
they are combined with they can either specify 
a reference time that precedes the speech time, 
as in 
(b) she came on Tuesday 
or a reference time that follows the speech 
time, as in 
(7) she comes/is coming/will cole on Tuesday 
Since there is only one reference time in the 
representation (= principle (I)) and since 
the when-adverbials always specify the reference 
time (= principle (IV)), it is predicted that a 
proposition can contain at most one when-adverbial. 
At first sight this prediction seems to hold: 
of. the ungrammaticality of 
(8) a. * He left yesterday one week ago 
b. * In 1990 he will have arrived in 1998 
c. * In 1955 he had died in 1944 
There are, however, some problem cases, such as 
(9) He left on Tuesday at 9 o'clock 
(10) Last year he used to arrive at 9 o'clock 
(9) contains two when-adverbials, but notice 
that they can be used together as an answer to 
one when-question, and this indicates that 
on Tuesday at 9 o'clock' is just a complex 
specification of one and the same interval. 
(10) is a more serious case. Here the two 
adverbials cannot be considered to specify the 
same interval: 'last year' denotes the time 
of his habit to arrive at 9 o'clock and 
"at 9 o'clock' denotes the time of each of his 
arrivals of last year. What we have in (10) is, 
2.2. The aspectual part. 
There is much discussion in the literature 
about what aspect is. A description that is 
nat very precise, but has the merit of being 
independent of linguistic form, is the one 
given by Coerie (1976, p. 3): 
'As the general definition of aspect, we may 
take the formulation that "aspects are 
different ways of viewing the internal 
temporal constituency of a situation". 
In an article on the general theory of 
aspect Friedrich distinguishes three 
possible aspects : 
(i) punctual, completive, perfective, etc; 
(ii) durative, continuative, etc; 
(iii) stative, perfect, etc. 
(of. Friedrich 1974, p. 36) 
The same three aspects turn up in the work 
of Coerie, 3ohnsan, Hopper, and others. 
We will call them respectively perfective, 
imperfective, and retrospective. 
The intuitions about the three are basically 
the following: 
(i) perfective 
This aspect presents a situation 'as a 
single unanalyzable whole' (Camrie, o.c., 
p. 3). 
(ii) imperfective: 
This aspect 'looks at the situation from the 
inside' (Comrie, op. tit, p.4), and focusses 
on beginning, continuation, or ending of it. 
(iii) retrospective: 
This aspect 'expresses a relation between two 
time-points, on the one hand the time of the 
state resulting from a prior situation, and 
on the other the time of that prior 
situation.' (ibid., p. 52). 
In order to make these nations more precise, 
and -at the same time- to integrate them into 
our representation format, we will adopt the 
following proposal by Johnson: 
'What I am proposing concerning the semantics 
of the aspect forms is that they specify the 
relation between reference time and event time 
in an utterance.' (Johnson 1981, p. 153) 
37 
As applied to the different aspects this 
gives the following results : 
(i) perfective: 
In th,s case we take the relation between E and 
R to be one of containment (during (E,R))twhere 
the latter is defined as follows: 
during ix,y) iff ~ t E time it s x ---> t e y) 
The fact that E is contained in R is meant to 
be the formal counterpart of the intuition that 
E is seen as a single unanalyzable whole from 
the point of view defined by R. 
(ii) imperfect(re: 
This is subdivided into three classes: 
ii.i) durative: contain (E,R), defined as in 2.1. 
(focus on the continuation) 
ii.ii) inchoative: since (E,R), definition: 
sinceix,y) iff x n y # 
& 3 t" E time ~ t e time it E x & t' E~y ---> t'<t) 
& 3 t E time ~ t' s time it ~ x & t' E y ---> t>t') 
ifocus on the beginning of E) 
iii.iii) terminative: Until iE,R), definition: 
untilix,y) iff x n y # e 
3 t e time ~ t' E time (t s x ~ t" E y ---> t(t') 
& 3 t" s time ~ t i time (t E x ~ t" E y ---> t'>t) 
(focus on the ending of E) 
(iii) retrospective: 
The relation is simply before (E,R). 
Some authors also distinguish a socalled 
'prospective' aspect (of. Comrie 1976). It 
seems to be less common than the other ones, 
and there is some disagreement on the issue 
of what its language specific counterparts 
are ('to be going to' ?), but conceptually 
it can be defined fairly easily, namely as 
the complement of the retrospective aspect: 
(iv) prospective: after (E,R) 
The interval E can be specified by 
adverbials. One class of E-specifiers is the 
class of duration adverbials. The reasons 
for treating these adverbials as 
E-specifiers are the following ones : 
I. they always denote the interval at which 
the basic proposition is said to take place; 
in that respect they are different from the 
when-adverbials, since the latter can also 
denote a time that does not coincide with the 
event time (of. the non-perfect(re aspects). 
2. they cannot be combined with all possible 
propositions; they are, for instance, not 
compatible with momentaneous events: 
(11) they reached the summit for a while 
The ungrammaticality of 411) can be explained 
if we take the duration adverbials to specify 
the event time, since the latter cannot be 
both a moment (as required by the proposition) 
and an interval of some duration las required 
by the adverbial). 
3. they never have a de(eric function: they 
are not used for specifying the relation 
between some interval and the.moment of speech. 
As in the case of the when-adverbials it is 
possible to have two duration adverbials in the 
same clause: 
(12) he has been studying two hours a day 
since his childhood now 
Notice, however, that i12) has an iterative 
interpretation, and since the treatment of 
such interpretations requires a more 
elaborated representation scheme anyway, 
we can stick to the principle that a clause 
contains at most one E-specifier. In this case 
the E-specifier is "since his childhood'; 
'two hours' is another type of specifier (cf. 
Van Eynde, forthcoming). 
2.3. The calculus as a whole. 
In the preceding sections it has been stipulated 
that there are three possible relations between 
S and R, and six possible relations between R 
and E. At first sight that seems to be rather 
arbitrary, but a careful analysis of the concepts 
involved shows that they, in fact, exhaust the 
range of logical possibilities : 
For any tuo intervals x and y c time, 
either x n y = 0 
and then either beforeix,y) 
or after (x,y) 
or x n y # 0 
and then either x c y, i.e. during(x,y~ 
or ~(x c y) 
and then either x = y, 
i.e. contain(x,yJ 
or -(x = y) 
and then either since~x,v~ 
or until ~x,y) 
These are the six aspectual values. The reason 
why the de(eric system has only three possible 
values is that the speech time - unlike the 
reference and the event time - is always a 
singleton, and if one of the intervals involved 
is a singleton, then the relations 'since and 
'until' and either "during' or 'contain' cannot 
hold by definition. It appears, thus, that both 
the deictic and the aspectual distinctions are 
not only mutually exclusive but also exhaustive 
within their respective domains. 
Together they form the core of the temporal 
calculus. This core has to be extended in 
various ways if one wants to take into 
account the phenomenon of iterativity, the 
sequence of tenses in complex sentences, and 
the relevance of the event type of the basic 
proposition (of. Vendler's distinction of 
38 
states, activities, accomplishments, 
achievements). Part of this has already been 
incorporated in the formalism, but in stead 
of presenting those extensions me think it 
more useful to round off this paper with a 
demonstration of how the calculus can be used 
for the interlingual analysis of verbal 
tense forms. 
3. The interlingual analysis of tenses. 
For the interlingual analysis of the verbal 
tense Torms #e adopt the following principle: 
(VII) 
The interlingual representations of verbal 
tense forms are pairs consisting of one 
deictic and one aspectual value. 
As the number of possible combinations of 
deictic and aspectual values is 18 (3x6), it 
follows that each tense form can have at 
most 18 different interlingual representations. 
In order to determine which values a given 
tense can actually have one has to examine 
its compatibility with the different types of 
time adverbials. 
As for the deictic subpart~ it is not so 
difficult to invent a criterion: 
(i) 
If tense X is compatible with a deictic 
Y-adverbial, ,here Y \[ (after, before, 
contain}, then the tense X can have the 
value Y. 
For the aspectual subpart the criteria are 
a bit more complicated: 
(ii) 
IT tense X can be used in a sentence with a 
when-adverbial in #hich the event is said to 
take place before or after the interval 
denoted by that when-adverbial, then the 
aspectual value of X can be either "before' 
or 'after', i.e. X can be used to express 
either retrospectivity or prospectivity. 
(iii~ 
If tense X can be used in a sentence which 
contains both a ,hen-adverbial and a duration 
adverbial that denotes an interval that is 
larger than the interval denoted by the 
when-adverbial, then tense X can be used to 
express the durative aspect. 
Similar criteria have to be stated for the 
other aspects (inchoative, terminative, and 
perfective). As far as ,e can see no# the 
perfective aspect might well be considered 
to be the default value: from a conceptual 
point of vie# the least marked situation 
is the one in which the event time is contained 
in or identical with the reference time 
(E c R or E = R). 
As an illustration of how these criteria can 
be used in practice we give an interlingual 
analysis of the Dutch 'Voltooid Tegenwoordige 
Tijd (VTT)'. This tense is expressed by the 
combination of an auxiliary ('hebben" or 
'zijn') and the perfect participle of a 
lexical verb. 
The VTT can be combined with all kinds of 
#hen-adverbials: 
(13) nu heb ik her gevonden 
now-have-l-it-found 
(14) morgen heb ik her gevonden 
tomorrow-have-I-it-found 
(15) gisteren heb ik het gevonden 
yesterday-have-l-it-found 
In (13) and (14) the time of event precedes 
the time denoted by resp. "nu" and "morgen"; 
hence, the aspectual value of the VTT in 
these sentences is the retrospective one. 
In fact, (13) and (14) belong to a paradigm 
of retrospective tenses. The other members 
of the paradigm are the "goltooid Verleden 
Tijd" and the "Voltooid Toekomende Tijd", 
as in 
(Ib) gisteren had ik bet al gevonden 
yesterday-had-l-it-already-found 
(17) morgen zal ik bet gevonden hebben 
tomorrow-shall-l-it-faund-have 
(14) and (17) even have the same meaning and, 
hence, the same interlingual representation, 
namely the combination after - before. 
(13) has the value contain - before, and 
(Ib) the value before - before. 
In (15) the situation is different: here, the 
time of finding does not precede the interval 
denoted by "yesterday" (as in (Ib)), but is 
rather contained in it. The aspectual value of 
the VTT in (16) is hence the perfective one, 
and the interlingual representation in that case 
is before - durin 9. 
It can further be sho,n that the VTT cannot be 
used to express a durative aspect. Comoare 
(18) gisteren ben ik de hele dag ziek geweest 
yesterday-am-l-the-whole-day-ill-been 
(19) * gisteren ben ik drie dagen ziek geweest 
yesterday-aa-l-three-days-ill-been 
In (18) the event time denoted by the duration 
adverbial "de hele dag" is a subset of the 
interval denoted by "gisteren" (= perfective 
aspect); in (19), on the other hand, the 
event time (three days) is said to be longer 
than the reference time (one day). Since this 
39 
combination leads to ungramaaticality (in 
Dutch), it follows that the VTT cannot express 
durativity. 
If these analyses are correct, it follows that 
the Dutch VTT can have three distinct inter- 
lingual representations: contain - before, 
after - before, and before - durino. 
The general idea now is that this information 
is contained in the lexicon, and that for the 
assignment of temporal representations to 
particular sentences one first looks in the 
lexicon to see which interlingual representations 
the tense used in that particular sentence can 
have, and then singles out that subset of 
representations which is compatible with the 
time adverbials used in the sentence. 
If that subset contains exactly one member the 
sentence may be said to be unaebiguous with 
respect to the temporal calculus; if the subset 
contains more members, the sentence is said to 
be temporally ambiguous; and if the subset is 
empty, the sentbnce is simply not well-formed. 
As a conclusion to this section we give the 
representations of some of the discussed 
sentences 
13) 3 S,R,E ~ time (contain(R,S) & nu(R) & 
before(E,R) & AT (E, ik her vinden)) 
15) 3 S,R,E S time (before(R,S) & gisteren(R) & 
during(E,R) & AT(E, ik het vinden)) 
(18) 3 S,R,E ~ time (before(R,S) & gisteren(R) & 
during(E,R) k de hele dag(E) 
& AT(E, ik ziek zijn)) 
Re÷erences 
Bruce, Bertram (1972) 'A model for temporal 
references and its application in a 
question answering program', in 
Artificial Intelligence 3, 1-25. 
Comrie, Bernard (1976) Aspect: an intro- 
duction to the study o÷ verbal aspect and 
related problems, Cambridge University 
Press, Cambridge. 
Dowry, David (1979) Word meaning and Montague 
grammar, Reidel, Dordrecht. 
van Eynde, Frank (forthcoming) Meaning and 
translatability, doctoral dissertation, 
Leuven. 
Friedrich, Paul (1974) 'On aspect theory and 
Homeric aspect', in International 3ournal 
of American Linguistics 40, memoir 28. 
Johnson, Marion (1981) 'A unified temporal 
theory of tense and aspect', in Tedeschi & 
Zaenen (eds.), Syntax and semantics. 
Volume 14. Tense and Aspect, Academic Press, 
New York. 
Kripke, Saul (1972) Naming and necessity, 
Harvard University Press, Cambridge Mass. 
Reichenbach, Hans (1947) Elements of symbolic 
logic, University of California Press, 
Berkeley. 
4. Prospects. 
In this paper we have concentrated on the 
definition of a conceptual calculus for the 
representation of time meanings in natural 
language. We have also given principles 
(IV,V,VI,VII) and criteria (i,ii,iii) for 
relating the concepts of the calculus to 
language specific morphosyntactic categories. 
Given these tools, it should be possible to 
analyse the tenses of the different languages 
in such a way that the results of the analysis 
are comparable and, indeed, identical iff they 
express the same concept. 
It goes without saying that the actual analysis 
of all possible tenses cannot be carried out 
in a paper of this size, but we have the 
feeling that ,e have at least cleared the 
ground for such an enterprise. 
40 
