The terms traditionally used to describe verb forms suit Latin very well, as in, for example, the forms derived from the base form ambulare, walk. Ambulat is present tense, ambulabit is future tense, ambulauerit is future pefect tense, ambulabat is imperfect tense, ambulauit is perfect tense and ambulauerat is pluperfect tense. These forms are characterised by various changes in the finite verb form to indicate the time at which whatever the verb describes takes place.
The terminology works up to a point with French. Marcher, for example, produces present tense marche, future tense marchera, imperfect tense marchait and past tense marcha, but to produce other forms, French cannot rely on the main verb alone. English can indicate tense by a change in the finite verb form only in the present (walks) and past (walked), while German can do so only in the present (geht) and imperfect (ging). Nevertheless, so strong has been the influence of the terms used for Latin, that their use has persisted in describing various verb forms in English and other modern languages. This is particularly so in course books for foreign learners, where it may be helpful. It is less helpful in any serious discussion of language because, at least in the case of English, it obscures the facts.
In ‘Language and Linguistics: The Key Facts’ R L Trask writes:
‘English has only two tenses: a “non-past” (present) mostly used for talking about present and future time, and a past tense, mostly used for talking about past time.’
In ‘Rediscover Grammar’ David Crystal writes:
‘English has only two tense forms: present and past.’
Both imply that a tense requires a change in the structure of the base form of the verb, and nothing else, as is the case in Latin. Consequently, their definitions do not cover such forms as he has walked, traditionally described in English, as in Latin, as the perfect tense. The authors of ‘The Cambridge Grammar of the English Language’, Rodney Huddleston and Geoffrey Pullum, depart from current orthodoxy in describing the perfect as a past tense, but most linguists describe all such forms only in terms of aspect. He has walked is said to show perfective aspect, suggesting that the speaker sees the act of walking as being completed, expressed through a form of the verb have followed by a past particple . Aspect can, in addition, be expressed through other forms of the verb: he walked also shows perfective aspect, as does he will walk.
In sentences such as He has walked, grammarians ancient and modern describe walked as the main verb and has as an auxiliary verb. I wonder if the time hasn’t now come to question that analysis. Instead of seeing it as a sentence on the pattern Subject – Verb, it seems to me entirely possible to see it as being on the pattern Subject – Verb – Object, with has as the main verb and walked as its object. In other words, we can take has as a lexical verb and consider that he has walked in his possession. Such an approach is perhaps clearer when the sentence expresses progressive aspect, as in he is walking. This we can analyse as being on the pattern Subject – Verb – Complement, with is as the main verb and walking as its complement, so tht he = walking, in the same way that in the sentence He is bald, he = bald. Even more complex clauses such as He will have been walking seem to me susceptible to this alternative treatment.