THE INTERPRETATION OF TENSE AND ASPECT IN ENGLISH 
Mary Dalrymple 
Artificial Intelligence Center 
SRI International 
333 Ravenswood Avenue 
Menlo Park, California 94025 USA 
ABSTRACT 
An analysis of English tense and aspect is pre- 
sented that specifies temporal precedence relations 
within a sentence. The relevant reference points 
for interpretation are taken to be the initial and 
terminal points of events in the world, as well as 
two "hypothetical" times: the perfect time (when 
a sentence contains perfect aspect) and the pro- 
gressive or during time. A method for providing 
temporal interpretation for nontensed elements in 
the sentence is also described. 
1. Introduction 
The analysis of tense and aspect requires spec- 
ifying what relations can or cannot hold among 
times and events, given a sentence describing those 
events. 1 For example, a specification of the mean- 
ing of the past-tense sentence "John ate a cake" 
involves the fact that the time of the main event - 
in this case, the cake-eating event - precedes the 
time of utterance of the sentence. Various pro- 
posals have also been made regarding the analysis 
of aspect which involve auxiliary times or events, 
whereby the proper relationship of these auxiliary 
times or events to "real" main events is specified. 
We provide an analysis of English tense and 
aspect that involves specifying relations among 
times rather than events. We also offer a means of 
interpreting tenseless elements like nouns and ad- 
jectives whose interpretation may be temporally 
dependent. For example, the noun phrase "the 
warm cakes" picks out different sets of cakes, de- 
pending on the time relative to which it'receives 
an interpretation. 
The analysis presented here has been imple- 
mented with the Prolog data base query system 
1The work presented here was supported by SP, I In- 
ternational. I am grateful to Phil Cohen, Bill Croft, Doug 
Edwards, Jerry Hobbe, Doug Moran, and Fernando Perelm 
for helpful discussion and comments. 
CHAT (Pereira 1983), and the representations are 
based on those used in that system. We shall 
show that an analysis of tense and aspect involv- 
ing specification of relations among times rather 
than among events results in a clean analysis of 
various types of sentences. 
2. Time Points 
Harper and Charniak (1986) \[henceforth H&C\] 
provide an interesting and revealing analysis of 
English tense and aspect involving relations be- 
tween events. There are several kinds of events: 
the u~terance event, which is associated with the 
time of the utterance; the main event, or the event 
being described by the main verb of the sentence; 
the perfecg event; and the progressivJe event. The 
representation of every sentence involves the ut- 
terance event and the main event; sentences with 
progressive or perfect aspect also involve progres- 
sive or perfect events. 
This treatment is quite different from the Re- 
ichenbach (1947) conception of "reference time", 
which is assumed to be relevant for all sentences. 
To translate between the two systems, the refer- 
ence time may be thought of as being represented 
by the perfect event in perfect sentences and by 
the progressive event in progressive sentences. In 
the case of perfect progressives, one might con- 
sider that there are two reference events, while in 
simple tenses there is no reference event at all. 
Alternatively, in a system like Webber (1987) in 
which reference points for each sentence are used 
to construct an event structure, the tensed event 
(what H&C call the "anchor event") is the rele- 
vant one: the perfect event for sentences with per- 
fect aspect; for sentences with progressive but no 
perfect aspect, the progressive event; or the main 
event for simple tense sentences. 2 
2 Although insta~s rather than events are used in the 
representation described here, a similar strategy would be 
employable in buildin 5 up a Webber-style event structure. 
68 
In accordance with H&C, we propose perfect 
reference points for sentences with perfect aspect 
and progressive reference points for sentences with 
progressive aspect. Thus, the interpretation of 
each sentence involves a number of relevant times: 
the beginning and end of the event described by 
the main verb for all sentences, the perfect time if 
it has perfect aspect, and the progressive time if 
it has progressive aspect. In our analysis, unlike 
H&C, what is relevant for the interpretation of 
sentences is not a set of events (which have po- 
tential duration and beginning and end points) 
but a set of times or instants. Instants, unlike 
events, have no beginning or end: they are one- 
dimensional points. This has several advantages 
over an analysis such as H&C, in which the per- 
fect and progressive reference points are events. 
First, if the reference points for perfect and pro- 
gressive sentences are events rather than instants, 
it ought to be possible to predicate duration of 
them. However, this is not a possible option for 
perfect and progressive sentences; durational ad- 
juncts are only interpreted relative to the main 
event. The sentence "John has swum for three 
hours" is only true when the duration of the main 
event (the swimming event) is three hours. 
Second, relations among events in H&C's sys- 
tem reduce anyway to relations between instants: 
the starting and ending points of events. That is, 
the primitives of systems like H&C's are relations 
among times. There seems to be little to be gained 
from constructing hypothetical events based on 
these relations when a simpler and cleaner analysis 
can be constructed on the basis of these primitive 
notions alone. 
There might seem to be the following objection 
to adopting times as relevant for the interpreta- 
tion of sentences: given a sentence like 'John was 
frosting a cake from 3:00 to 4:00 yesterday', we 
know about the progressive reference point only 
that it lies between 3:00 and 4:00; there are in- 
finitely many instants satisfying that condition. 
It would be impossible to iterate over all of these 
times to determine the truth of any utterance. In 
fact, though, to determine whether a sentence con- 
taining perfect or progressive aspect is true, it is 
unnecessary to instantiate the perfect or progres- 
sive reference times to specific values; it suffices to 
show that an interval exists within which such a 
point can be found. That is, they are merely ex- 
istentially quantified, not instantiated to a value. 
In this manner, perfect or progressive times may 
give the appearance of being similar to events with 
a starting and an ending point, because they are 
constrained only to exist within some nonnull in- 
terval. Checking whether or not the sentence is 
true involves determining whether the interval ex- 
ists. 
The following is the representation for the sim- 
ple past sentence "John frosted a cake", with 
words in upper case representing variables and 
words in lower case representing predicate names 
or constants: 
(1) ezists X Start End 
holds(frost(john, X), Start, End) 
g_4 cake(X) 
g~ precede(End, now) 
The predicate holds in the first clause of the repre- 
sentation takes three arguments, representing the 
predicate and the beginning and ending times of 
the event. In other words, John frosted X from 
time Start to time End. The predicate cake(X) 
specifies that the thing John frosted was a cake. 
We do not represent this with a holds predicate 
because we assume that the property of being a 
cake is a static property, not one that changes over 
time.S 
The predicate precede(End, now) specifies that 
the ending time End of the cake-frosting event 
must precede now, the current time. In the course 
of validating this logical form, the variable End 
will be instantiated to a numerical value, and the 
atom now will be replaced by the value of the cur- 
rent time. The predicate precede represents the 
less-than-or-equal-to relation, while the predicate 
strictly.precede represents the leas-than relation. 
Thus, the cake-frosting event must occur in the 
past. 
Let us next consider the semantic representation 
of a sentence with perfect aspect, "John will have 
frosted a cake": 
(2) ezists X Start End Perfect 
holds(frost(john, X), Start, End) 
cake(X) 
g~ precede(End, Perfect) 
strictly_precede(now, Perfect) 
3Th\]s is not a necessary part of the analysis; the repre- 
sentation has been chosen in part for the sake of simplicity. 
It would also be possible to represent the predicate cake(X) 
inside a holdJ predicate, with the Start and End tlmes rep- 
rosent~ag when the cake began and ceased to exist. 
69 
The interpretation of perfect sentences involves 
a perfect time Perfect. This time is constrained 
to follow the main event; this is enforced by the 
clause precede(End, Perfect). Since this is a future 
perfect sentence, Perfect is constrained to be in 
the future. The future tense is represented by the 
predicate strictly_precede; the perfect time must 
follow now (not coincide with it). 
Note, therefore, that in the case of future per- 
fect sentences the main event is required only to 
end before a time in the future, and that (as with 
H&C) it is not a contradiction to say "John will 
have arrived by tomorrow, and he may already 
have arrived." Unlike analyses in which relations 
among all reference points are fully specified, this 
analysis allows the main event to be in the past 
even though the sentence itself is in the future per- 
fect. 
The following is a representation of the past pro- 
gressive "John was frosting a cake": 
(3) e~ists X Start End Progressive 
holds(frost(john, X), Start, End) 
cake(X) 
precede(Start, Progressive) 
precede(Progressive, End) 
precede(Progressive, note) 
Here the progressive time, represented by the 
variable Progressive, must occur during the cake- 
frosting event; that is, it must occur after the start 
and before the end of the main event. Since the 
sentence is a past progressive, there is a final re- 
quirement on Progressive: it must precede note. 
Notice that past progressives differ from simple 
past sentences in that it is the progressive time 
and not the ending time of the main event that 
is required to be in the past. Consequently, as in 
H&~C, the interpretation of a past progressive like 
"John was frosting a cake" does not require that 
the main event lie entirely in the past, but only 
that some part of it he in the past. The present 
analysis allows for the possibility that sentences 
like the following can be true: 
(4) John was frosting a cake at 3:00, and he is 
still frosting it. 
We shall see in the next section that what was 
referred to as the progressive time in the forego- 
ing example actually appears in the representation 
not only of progressives, but of every sentence, as 
what we shall call the during time. The during 
time will be used in the temporal interpretation of 
nontensed elements in the sentence. For this rea- 
son, the above representations of the simple past 
and future perfect sentences above were only a first 
approximation; actually, their complete represen- 
tations also contain a during time. 
Finally, the representation of a sentence with 
both progressive and perfect aspect, like "John 
will have been frosting a cake", is the following: 
(5) exists X Start End Progressive Perfect 
holds(frost(john, X), Start, End) 
cake(X) 
precede(Start, Progressive) 
precede(Progressive, End) 
precede(Progressive, Perfect) 
strictly.precede(now, Perfect) 
Progressive, the progressive or during time, occurs 
during the cake-frosting event. Progressive is con- 
strained by the clause precede(Progressive, Per- 
fect) to precede the perfect time Perfect. In other 
words, for a perfect progressive sentence, the re- 
quirement is that some portion of the main event 
lie before the perfect time. The perfect time is con- 
strained by the clause strictly_precede(now, Per- 
fect) to lie in the future. 
In this analysis, underspecification of relations 
among times yields results that match the natural- 
language semantics of sentences. 4 Use of a perfect 
and a progressive time allows uniform treatment 
of perfects and progressives without the compli- 
cation of introducing unwarranted pseudo-events 
into the representation of simple tenses. Also, the 
progressive/during time is useful as an anchor for 
the interpretation of nontensed elements, as we 
will see below. 
3. Temporal Interpretation of Nontensed 
Elements 
Not only tensed verbs, but also other nontensed 
elements in the sentence - adjectives, nouns, 
prepositions, and so on - must be temporally in- 
terpreted. Consider the sentence "Are there any 
warm cakes?" The adjective "warm" must be in- 
terpreted relative to some time: in this case, the 
4 We have not yet enriched the representation of individ- 
ual predicates to include inherent aspect, as described in, 
for example, Pammneau (1987). We feel, though, that the 
resulting representatione will sti~ involve the tree of perfect 
and during times, and will still be amenable to the treat~ 
merit of nontensed elemclats described in the next section. 
70 
present. The question is about cakes that are cur- 
rently warm. 
The interpretation of nontensed elements does 
not always depend on the utterance time, though. 
The sentence "The third-year students had to take 
an exam last year" can be interpreted in two ways. 
Under one interpretation, those who were third- 
year students last year (the current fourth-year 
students) had to take a test last year. The inter- 
pretation of the noun phrase "the third-year stu- 
dents" is dependent on the tense of the main verb 
in this case. Under the other interpretation, those 
who are currently third-year students took a test 
last year, when they were second-year students. 
However, the interpretation of nontensed ele- 
ments with respect to the tense of the main verb 
in the sentence is not entirely unconstrained. Con- 
sider the sentence "The wife of the president was 
working in K-Mart in 1975." "Wife" and '~)resi- 
dent" are both predicates that must be interpreted 
with respect to a particular time. The current 
president is not the same as the 1975 president; 
if he divorced and remarried, his 1975 wife is not 
necessarily the same person as his current wife. 
Given this, there ought to be four possible inter- 
pretations of this sentence. In fact, there are only 
three: 
* He is the current president and she is his cur- 
rent wife 
• He is the current president and she was his 
wife in 1975 
• He was the president in 1975 and she was 
his wife then (but perhaps he is divorced and no 
longer president) 
The missing interpretation is that 
• He was the president in 1975 and she is his 
current wife (but was not his wife then) 
A skeletal tree for this example is shown in Fig- 
ure 1. The sentence involves the syntactic embed- 
ding of one NP ("the president") inside another 
NP ("the wife"). The unavailable interpretation 
is one in which the embedded NP is interpreted 
with respect to the event time of the higher verb, 
whereas the intervening NP is not. That is, the 
unavailable interpretation involves interpreting a 
discontinuous portion of the parse tree of the sen- 
tence with respect to the main verb. 5 
s As we will see in the next section, it is possible to con- 
struct ~ context in which the "missing interpretation" is in 
fact available for this sentence. The clahn ~,~\]e here is that 
this interpretation is not available by means of the syntactic 
variable-passing mechanism discussed in this section, but 
One may think of the main-verb event time as 
being passed or disseminated through the tree. It 
may be passed down to embedded predicates in 
the tree only when it is passed through interme- 
diate predicates and used in their interpretation. 
If a predication is interpreted with respect to the 
current time rather than to the event time of the 
main verb, all predications that are syntactically 
subordinate to it are also interpreted with respect 
to the current time. When this happens, the main- 
verb event time ceases to be passed down and may 
not be reinstated for interpretation. 
Note, however, that the verb time and the time 
with respect to which the nontensed elements are 
interpreted are not always completely coextensive. 
Consider again the example "John will be frost- 
ing a warm cake at 3:00." Under the interpreta- 
tion that the cake is warm while John is frosting 
it, the time span during which the cake is warm 
must include the time 3:00; however, the starting 
and ending points of the cake-frosting event need 
not coincide exactly with the starting and ending 
points of the interval at which the cake is warm. 
The only requirement is that both events must 
hold at 3:00. 
Now consider the sentence "John built a new 
house." The building event can be thought of as 
beginning before the event of the house's being 
new. At the start of the building event, there is 
no house, nor, obviously, is there is any event of 
the house's being new. In a situation like this, one 
does not want to require that the building event 
be coextensive with the event of the house's being 
new, but rather, merely to require that the two 
events should overlap. 
Our claim is that, in general, temporal interpre- 
tation of nontensed elements relative to the tense 
of the main verb of the sentence requires only that 
the event denoted by the main verb overlap (not be 
coextensive with or be contained in) the events de- 
noted by the nontensed elements. We shall accom- 
plish this by positing a time for each tensed verb, 
the during time, and passing this time through the 
syntactic tree. The event denoted by the main 
verb, as well as the events denoted by any predi- 
cates interpreted relative to the main verb, must 
hold at this during time. 
For example, here is the logical form for the sen- 
tence "John frosted a warm cake" : 
is only ~vailable by appea~ to the context constructed. 
The %nixing interpretation" is missing when there is no 
context to refe~ to for addition~ interpretations. 
71 
S 
NP 
y ~pp 
thewife / ~ 
P NP 
t 
of tl~e president 
VP 
was working in K-Mart in 1975 
Figure 1 
(6) ezists X Startl End1 Slart~ End~ During 
holds(frost(john, X), Start1, End1) cake(X) 
precede(End1, now) 
precede(Start1, During) 
precede(Daring, End) 
hotdsCwarmCX), Szar~, End~) 
precede(S~artl, During) 
precede(Daring, End) 
There are two predicates in this example that 
are interpreted with respect to a temporal inter- 
val: warm and frost. There must be a during time 
During that occurs during both the cake-frosting 
event and the event of the cake's being warm: the 
two events must overlap. 
We further note that all elements within a NP 
node are interpreted with respect to the same 
event. It is not possible, for example, to interpret 
some elements of a noun phrase with respect to the 
time of utterance, others with respect to the main 
verb's during time. Consider the sentence "John 
frosted three stale warm cakes yesterday." Despite 
the pragmatic predilection for interpreting "stale" 
and "warm" at different times (it is hard to imag- 
ine how cakes that are still warm could already be 
stale), this sentence has only two interpretations: 
• John frosted three cakes that were both stale 
and warm yesterday. 
• John frosted three cakes yesterday that are 
both stale and warm now. 
It is not possible to give the sentence the interpre- 
tation that the cakes he frosted were warm yes- 
terday and are stale now, or were stale yesterday 
and are warm now. Both adjectives must be in- 
terpreted with respect to the same time. 
If a system like H&C, in which events and 
not instants are taken to be the relevant refer- 
ence points, were extended to include interpre- 
tation of nontensed elements as described here, 
such a system might use primitives such as those 
of Allen (1984). However, none of the primi- 
tives of Allen's system is suitable for defining the 
relation of the during time to the main event: 
during(DuringEvent, MainEvent) is not sufficient, 
since Allen's "during" relation does not permit the 
DuringEvent to coincide with the beginning or end 
points of the main event. The example "John 
built a new house" shows that this is necessary; 
in this case, it is precisely the end point of the 
building event that coincides with the beginning 
of the event of the house being new. In a system 
using Allen's primitives, the proper relation be- 
tween the DuringEvent and the MainEvent would 
be a disjunction: 
(7) during(DuringEvent, MainEvent) OR 
starts(DuringEvent, MainEvent) OR 
ends(DuringEvent, MainEvent) 
4. Passing the During Time: Rules for 
Temporal Interpretation 
In the previous section, we examined the tem- 
poral interpretation of phrases with respect to 
the during time of the main verb. In addition, 
72 
we proposed a constraint on the passing of this 
during time from the verb through its arguments 
and adjuncts, according to which predicates inter- 
preted according to the during time must occupy 
a nondiscontinuous portion of the tree. From the 
point of view of the tenseless phrase, however, the 
same process can be seen in a different light. 
We may think of the interpretation of tempo- 
rally dependent elements in.a phrase as proceeding 
in the following manner: 
• The phrase is interpreted with respect to a 
temporal modifier internal to the phrase; other- 
wise 
• The phrase is interpreted with respect to the 
closest higher tensed element (allowing for restric- 
tions on the distribution of the during variable); 
otherwise 
• The phrase is interpreted with respect to some 
contextually relevant time. 
Temporally dependent nontensed elements in 
previous sections were always contained in phrases 
that lacked internal temporal modifiers, so the first 
option was not applicable. One of two interpreta- 
tions was given for tenseless elements: they were 
interpreted either with respect to the during time 
of the main verb or with respect to now, the time 
of utterance. Interpretation with respect to now 
seems to be a particular instance of the general 
possibifity of interpretation with respect to a con- 
textually relevant time; since no context was given 
for the examples in the previous sections, no other 
contextually relevant time was available. When a 
phrase contains a phrase-internal temporal modi- 
fier, the predicates in that phrase must be inter- 
preted with respect to that modifier, as in the ex- 
ample "The 1975 president is living in California." 
The modifier "1975" in the phrase "the 1975 pres- 
ident" provides the temporal interpretation of the 
phrase: it must be interpreted with respect to that 
time. It is not possible to interpret "president" 
relative to the during time of the main verb. 
Hinrichs (1987) also proposes that noun phrases 
be interpreted relative to a time restricted by the 
context; the difference between his analysis and 
ours is that, of the three options presented above, 
he offers only the last. He contends that the only 
option for temporal interpretation of nontensed el- 
ements is the third one, namely, by reference to 
context. 
Given an analysis like that of Hinrichs, it is dif- 
ficult to explain the facts noted in the preceding 
section. In the absence of context (or when the 
sole context is the moment of utterance), Hinrichs 
would not predict the absence of one reading for 
sentences such as "The wife of the president was 
working in K-Mart in 1975." In an analysis like 
the one presented here, where the interpretation 
of nontensed elements is determinable in some in- 
stances through syntactic processes, the absence 
of these readings is expected. 
Enc (1981) and Hinrichs (1987) both argue con- 
vincingly that there are many instances in which a 
temporally dependent element is interpreted with 
respect to a time that is neither the during time 
nor now. Hinrichs furnishes the following example: 
(8) Oliver North's secretary testified before the 
committee. 
At the time she testified, she was no longer his sec- 
retary; she-was also not his secretary at the time 
this sentence was uttered. The sentence would re- 
ceive the following interpretation: 
(9) exists X Startl End1 Duringl 
Start2 End~ During2 
holds(secretary(north, X), Start1, End1) 
precede(Start1, Duringl) 
precede(During1, End1) 
~4 hotdsOestify(X), StartS, End2) 
g~ precede(Start2, During~) 
g~ precede(During2, End~) 
precede(During2, now) 
There are two events described in the logical form 
of this sentence: the event of X being North's sec- 
retary and the event of X testifying. Daring1 is a 
time during the being-a-secretary event, and Dur- 
ing2 is a time during the testifying event. The 
events are not required to overlap, and only the 
"testify" event is restricted by the tense of the 
sentence to occur in the past. In a more complete 
representation, appropriate restrictions would be 
imposed on During1: the time during which X is 
a secretary would be restricted by the context, in 
line with Hinrichs' suggestions. 
5. Further Results 
It appears that the during time of the main 
clause is used in the interpretation of some tensed 
subordinate clauses: for example, in the interpre- 
tation of relative clauses. Consider the sentence 
"He will catch the dog that is running." Under 
one interpretation of this sentence, the catching 
event is simultaneous with the running event - 
73 
both events take place in the future. In this case, 
the interpretation of the main verb in the relative 
clause depends on the during time of the main 
clause. There is also another interpretation, ac- 
cording to which the dog that will be caught later 
is running now. In this case, the interpretation of 
the relative clause depends on the time of utter- 
ance of the sentence. 
One remaining task is to provide a reasonable 
analysis of the bare present using this system. We 
feel that such an analysis awaits the incorporation 
of a representation of inherent lexical aspect as in 
Passoneau (1987); without a representation of the 
distinction between (for example) states and activ- 
ities, a coherent representation of simple present 
tense sentences is not possible. 
7. Conclusion 
We have shown that distributing an existen- 
tially quantified during~time variable throughout 
the tree enables interpretation of nontensed ele- 
ments in the sentence according to the time of the 
main verb. Further, the during time is useful in the 
interpretation of several sentence types: progres- 
sivss, statives, and sentences containing relative 
clauses. Finally, an analysis that utilizes under- 
specified relations among times (not events) pro- 
vides a good prospect for analyzing tense and as- 
pect in English. 
rina Del Rey, California.: Information Sciences In- 
stitute. 
Passoneau, Rebecca. 1987. "Situations and 
Intervals." Proceedings of the ACL Conference, 
Stanford University, Stanford, California. 
Pereira, Fernando. 1983. "Logic for Natural 
Language Analysis." Technical Note 275. Menlo 
Park, California.: SRI International. 
Reichenbach, Hans. 1947. Elements of Symbolic 
Logic. New York, New York: Macmillan. 
Webber, Bonnie. 1987. "The Interpretation of 
Tense in Discourse." Proceedings of the ACL Con- 
ference, Stanford University, Stanford, California. 
References 
Allen, James F. 1984. "Towards a General The- 
ory of Action and Time." Artificial Intelligence 
23:2, July 1984. 
Enc, Murvet. 1981. "Tense without Scope: An 
Analysis of Nouns as Indexicals." Ph.D. disserta- 
tion, University of Wisconsin, Madison, Wiscon- 
sin. 
Harper, Mary P. and Eugene Charniak. 1986. 
"Time and Tense in English." Proceedings of the 
ACL Conference, Columbia University, New York, 
New York. 
Hinrichs, Erhard. 1987. "A Compositional 
Semantics of Temporal Expressions in English." 
Proceedings of the ACL Conference, Stanford Uni- 
versity, Stanford, California. 
Mathiessen, Christian. 1984. "Choosing Tense 
in English." ISI Research Report RR-84-143. Ma- 
74 
