CHAPTER 6

The Tense of Verbs

6.1 Verb Structure

The forms of verbs in which we are interested are:




The verb 'to move' has been chosen for illustration because it is relevant to our discussion of screen displays and because it is a regular verb. Each of these verb forms contains a main verb (a form of the verb 'to move') and possibly several auxiliary verbs (forms of the verbs 'to be' and 'to have'). Each describes a similar action (movement) but different forms carry different implications with respect to the following factors:

(a) Time (or tense) - whether the action is in the present, past, future or neutral with respect to some reference point in relative time, which is the current focus of attention. A neutral tense mark leaves the tense undefined. (b) Continuing - whether the action continues or continued over a period of time.

(c) Finished - whether or not the action has been completed.

(d) Active/Passive (or voice) - whether the reference-object is playing an active or passive role. In the case of an inanimate object such as a triangle, the active form 'it is moving' merely leaves unstated who or what is responsible for the movement, but in the case of an animate object, the active form declares it to be the cause of the movement.

An ATN for the structure of the verb group is shown in Figure 9.7 and a grammar is provided in section 9.4.

6.2 Marking

In linguistics it is said that the various verb and word forms are 'marked' with these semantic factors. Taking the set off actors, or marks, listed in the previous section we can characterise every verb form by means of a four-term symbol:

(a) The time-stamp is denoted (Now/Past/Future) or (N/P/F)

(b) The Continuingjnot-continuing is denoted by (C/-)

(c) The Finished action/not finished action is denoted (FI-)

(d) The Active/Passive factor is denoted (AlP)

We can then write down all possible permutations of these factors to obtain the following table:




Some of these (with a question mark) are distinctly clumsy, and it is questionable if they would be accepted as grammatical English. Nevertheless they represent intelligible English. The pattern of these forms is clear.

Main verb endings:

'...ing' denotes the continuing factor.

'...ed' denotes the past and the fmished factors unless the verb is immediately preceded by a form of the verb 'to be', in which case it denotes the passive and the fInished factors.

' ... s' denotes present tense (or it is neutral with respect to time indicating that the object is capable of being moved and does so from time to time). Note that there are forms (e.g.: I move) in which the verb has no ending, but which should be interpreted as though it had an's' ending (e.g.: it moves). The function 'sterrumd' might be modified accordingly.

The auxiliary verbs 'to be' and 'to have' also have time, continuing and finished marked forms:




In an ideal information communication system designed for maximum flexibility and no ambiguity, any flags or mark indicators such as word endings would be orthogonal. That is, they would each be associated with a single type of mark and could be used freely without it being necessary to take into account the other flags which may occur in the same segment of text. This is not the case in English because, for example, the word ending' ...ed' can be used both to indicate 'past tense' and 'action finished'. It is also used to indicate 'passive voice' (in association with the verb 'to be'). This double use of a flag means that additional flags must be inserted when both the marks associated with '...ed' are required.

For example, if we require both passive voice and the 'continuing' mark we cannot use both the endings '.. .ed' and '. :,.ing' on the main verb. We therefore use the '...ed' ending to denote passive voice and add the '...ing' ending on to the auxiliary verb to give 'being moved.'

The fact that some of the verb forms shown above are grammatically suspect reflects the fact that they describe a relatively rare state of affairs which is difficult for humans to envisage. Careful thought will, however, show that they do have an intelligible meaning.

In the case of verbs in which the difference between active and passive forms is crucial (e.g. 'takes') the active/passive form may be distinct from the past-tense form.

For example:




The verb form 'taken' normally carries a mark for passive voice, and if it is used to carry the past-tense mark for the verb as a whole, the passive voice mark must be cancelled by preceding it with a form of the verb 'to have'. For example, 'he has taken' is not identical to 'he took'. In the case of 'he has taken' the focus of attention is still 'now', (i.e. we are discussing an historical event relative to the current focus of interest). In the case of 'he took' we are discussing an historical event only. In most cases the distinction is too subtle to prevent the two forms being substituted for each other, but the distinction can be seen in the examples below:

'He took the book and he read it.'

'He has taken the book and it cannot be found.' 'He has taken the book and he read it.'

'He took the book and it cannot be found.'

All four of these sentences are grammatical and understandable, but the second two are slightly odd in that they appear to switch emphasis from the present to the past or vice-versa, whereas the flISt two focus on a single time reference. The fourth sentence is quite acceptable, however, because the switch is made from a past event to a present consequence of that event.



6.3 Time Displacement

The notion of a time displacement noted against 'be' and 'have' reflects the fact mentioned above, that all these notions of past, present and future are expressed as being relative to some relative-time reference point (or pseudo-present - see Chapter 4). There can be more than one reference point within the verb form. For example the verb form 'will have been moving' has more than one reference point. The auxiliary verb 'will' generates a new reference point (say Tl) which is in the future with reference to 'now' ('now' is the relative time associated with the focus of interest). 'Have' being neutral, preserves T1. 'Been' generates a new reference point (say T2) in the past relative to T1. 'Moving' adds the continuing factor and adopts the reference point T2 as the time-stamp of the action. The verb as a whole indicates that at some time in the future Tl (relative to 'now') 'it' will be in a state in which it 'has been moving' (at time T2). There is no indication whether or not T2 is before or after 'now'. All we know is that at Tl the object of reference ('it') will have the movement (at T2) as part of its history.

Figure 9.7 illustrates the ATN which analyses the structure of a verb. Figure 6.1 is a simplified version of this. The reader is invited to develop a POPll or Prolog program which will correspond to the diagrams in Figure 6.1.

The program should accept a verb in any of the forms illustrated above and should yield as its result the three items:




The program should also create a side-effect which updates a data structure of four elements:

T,C,F,AP corresponding to the four factors Time, Continuing, Finished, Active/Passive




6.4 Using the Verb Factor Analysis to aid a Search

We have discussed in previous chapters the interpretation of the pronominal reference 'it' and the verb 'move'. Consider the interpretation of a statement which begins 'Before moving it ...'. The statement requires a referent for 'it', and the only clue is that it is something which has been moved. It will be necessary therefore to search back in the internal text for something which was moved. The verb 'moving' will be associated with a structural pattern, which can be used as a template for a pattern matching search to find a reference-object for 'it'.

The verb factors will provide further aids for the search. In the case of 'before moving it. . .', we do not know whether or not the action is in the past or the future. If the statement had begun 'Before it was moved. . .' we would know it had taken place in the past, and the search would be directed backwards. It will also indicate whether the action is spread over a period of time (continuing) and whether at the time of interest it has been terminated or not (finished). The active/passive factor is not relevant to our particular example because the reference-object (e.g. triangle) is not animate, and in normal circumstances cannot be regarded as responsible for any actions. Had we been discussing animated cartoons, however, we might have had a use for the active/passive factor.

6.5 Agreement with Subject

We have not dealt with another aspect of verb structure - the way the form of the verb is chosen to agree with the nature of the subject (person: 1st, 2nd or 3rd person; number: singular or plural) of the sentence. For example:

I go

He goes

This can be an additional mark placed on the verb form. The reader might now turn back to the sample of irregular verb forms (section 5.3) and complete the table by adding a new column labelled 'person' and 'number'.




The programs written for the 'stem_end' function should also be modified so that they update a global register with the information concerning person and number. Not all verb forms provide information of this kind, and so it will be necessary to provide a mark indicating that several types of 'person' are allowed. One way to achieve this is to use an octal numbering system so that each bit of the octal number corresponds to a person classification, so that:




A similar arrangement can be used for the 'number' mark.