Present tense

DEFINITION24. The notions ‘true’ and ‘false’ can be applied to tensed

sentences in the following manner. The tensed sentence is true if the in- tegrity constraint can be satisfied; it is false if there is no way to satisfy the integrity constraint6.

Since sentences are modelled as integrity constraints, the entailment re- lation between sentences ϕk, ϕl translates into an entailment relation be- tween integrity constraintsICk, ICl for instance of the form ‘given a sce- narioS, ifICksucceeds, thenIClsucceeds’, or ‘given a scenarioS, ifICk fails, thenIClsucceeds’– there are four cases in all. Take the first example. We are given a scenarioS, and we assume thatICkcan be made to succeed. This leads to a minimal extension S! _{ofS in whichIC}

k in fact succeeds. We then require thatIClalso succeeds inS!. The other cases have a similar meaning. For example, in Section 2 we will study the inference from (8-a) to (8-b)

(8) a. John is crossing the street. b. John will have crossed the street.

The first sentence is characterized by the integrity constraint that the ref- erence time equalsnowand is contained in the activity crossing, while for the second sentence the reference time is in the future and is situated in the state resulting from the completion of the crossing. Dowty posited that the inference from (8-a) to (8-b) is valid with respect to ‘inertia worlds’ (see the discussion in Section 2 below); here, validity is with respect to scenarios and their minimal models. In particular, given the scenario S for ‘cross the street’, sentence (8-a) introduces the integrity constraint that

?HoldsAt(crossing,now) must succeed. This has the effect of extending

S with a statementHappens(start, t0)for somet0 <now. In the resulting

extended scenarioS!, the query?Happens(reach, t), t >now (representing sentence (8-b)) leads to a successful computation.

3. Present tense

In the following it will be useful to distinguish between the syntactic and the semantic present tense. By definition, in semantic present tense the utterance time, the event time and the reference time all coincide. The use of the syntactic present tense is however not confined to cases where this meaning is appropriate. There is for instance the future use of the present tense inTomorrow I fly to London, which will be treated below in Section 5. Furthermore, accomplishments and activities in the syntactic present tense generally have habitual meaning, as in I sing on Sundays. It is doubtful whether tense is used deictically here, referring tonow(for a contrary view see Comrie [18, [p. 39]). It rather seems to be anaphoric to a timeperiod, as in

6_{**Some computations may loop, and therefore tensed sentences may in principle be} neither true nor false. In practice this does not present a problem.**

108 8. TENSE

(9) This year I sing on Sundays, but last year I sang on Wednesdays.

The characteristic feature of habituals appears to be that they explicitly re- fer to a plan to be executed repeatedly during a given period. Some planned executions of the plan may fail to take place, but that does not make (9) false. There also appears to be a subtle difference in the ways plans are involved in habituals and in the semantics for accomplishments. An expres- sion such as ‘write a letter’ intends to refer to the real process of writing a letter, even though that process is coded semantically by means of a plan, i.e. the steps that have to be executed. In contrast to this, the habitual refers to the plan itself, not so much to the real-world events constituting the exe- cution of the plan. In principle it is possible to represent this distinction in our framework, since we have enough machinery available to code a plan (i.e. a scenario plus the axioms of the event calculus) into a single object, but we shall not do so here since it is somewhat involved.

In English, use of the syntactic present tense is rather restricted. The syntactic present tense cannot be used with accomplishments and activities to express that utterance time, reference time and event time coincide, even though this semantic content can be expressed by means of the present pro- gressive, as we will see below. When achievements and points are used in the syntactic present tense, the resulting construction can have a mean- ing superficially similar to that of the semantic present tense. This happens for instance if the achievement is a performative verb such as ‘name’ or ‘promise’:

(10) a. I name this ship the ‘Titanic’.

b. I promise to give you ten pounds before tomorrow 12 noon.

because the act of promising clearly coincides with the utterance of the sen- tence. But especially in the case of (10-b) this is not exactly the semantic present tense, because the reference time, which corresponds to ‘give you ten pounds’, is situated in the future, and (hopefully) before tomorrow 12 noon. In fact this is almost a paradigm case of the formalization of refer- ence time as an integrity constraint, since we are clearly concerned with an obligation here.

Another case in which the present tense is used, is in a simultaneous report of events that are currently going on, as in a live broadcast of an Arsenal match

(11) Henry reaches Bergkamp. Bergkamp takes the ball, shifts it to his other foot, shoots7. . . goal!

Again this is a very special use of the present tense: obviously utterance time and event time coincide, but in this case reference time does not even have a meaning. Apart from these cases, use of the semantic present tense

3. PRESENT TENSE 109