The eight simple forms can also be categorized into four tenses (future, present, past, and future-of-the-past), or into two aspects (perfective and imperfective).
The ending depends on the mood, tense, aspect, and voice of the verb, as well as on the person and number of its subject.
Every conjugation exhibits some degree of syncretism, where the same (homophonous, and possibly also homographic) form is used to realize distinct combinations of grammatical features.
The prevalence of syncretism in conjugation paradigms is one functional explanation for the fact that French does not allow null subjects, unlike most of the other Romance languages.
In French, « Je le ferais si j'avais assez de temps » is "I would do it if I had enough time" in English.
The conditional can also be used evidentially, to express reservations about the verb: « Il serait suivi par un psychologue », "He is apparently/is said to be/[etc.]
[citation needed] A third camp recognizes both "conditionnel présent/conditionnel passé" (for use in conditional sentences), and "indicatif futur du passé / indicatif futur antérieur du passé" (for tense concords, "future from a past point of view"; e.g. « Il m'a dit qu'il le ferait le lendemain », "He told me he would do it the next day"), but they recognize also that both are conjugated the same.
Note that, as discussed above, in some uses the conditional can be considered a separate mood completely, while in other uses it is the future-in-past tense of the indicative.
These tense forms are used to indicate events before the corresponding simple tense forms; for example, « À ce moment-là, il se souvint de ce qu'il avait promis » ("At that moment, he remembered what he had promised").
In addition, except in literature or very formal speeches, the present perfect form is used in modern French wherever the simple past would have been used in older or more literary writing.
Since this use is much more common than its use as a true present perfect, it is usually called the compound past (le passé composé).
Further, where older or more literary French would have used the perfect form of the simple past tense (le passé antérieur) for the past-of-the-past, modern non-literary French uses the pluperfect (le plus-que-parfait; the perfect of the imperfect), or sometimes a new form called the surcomposé (literally, "over-compound"), which re-applies the perfect to the compound past, resulting in a structure like « Je l'ai eu fait » (literally, "I it have had done").
(For example, "I am doing it" might be expressed as « Je suis en train de le faire », "I am in the middle of doing it.")
Of these, only the present is used nowadays; like the simple past indicative, the imperfect subjunctive is only found in older and more literary works.
The imperative only has a present tense, with a rarely used perfect: "fais-le" and "aie-le fait" both mean "do it", with the latter implying a certain deadline (somewhat like English "have it done").
A small number of verbs, including some already mentioned above, can in fact be found with either auxiliary (croître, monter, descendre, convenir, paraître, apparaître, trépasser).
The distinction between the two auxiliary verbs is important for the correct formation of the compound tense-aspect forms and is essential to the agreement of the past participle.