a) The Present Infinitive represents an act as contemporaneous with the time of the verb on which it depends; as,—
vidētur honōrēs adsequī, he seems to be gaining honors;
vidēbātur honōrēs adsequī, he seemed to be gaining honors.
b) The Perfect Infinitive represents an act as prior to the time of the verb on which it depends; as,—
vidētur honōrēs adsecūtus esse, he seems to have gained honors;
vīsus est honōrēs adsecūtus esse, he seemed to have gained honors.
c) The Future Infinitive represents an act as subsequent to that of the verb on which it depends; as,—
vidētur honōrēs adsecūtūrus esse, he seems to be about to gain honors;
vīsus est honōrēs adsecūtūrus esse, he seemed to be about to gain honors.
2. Where the English says 'ought to have done,' 'might have done,' etc., the Latin uses dēbuī, oportuit, potuī (dēbēbam, oportēbat, poteram), with the Present Infinitive; as,—
dēbuit dīcere, he ought to have said (lit. owed it to say);
opōrtuit venīre, he ought to have come;
potuit vidēre, he might have seen.
a. Oportuit, volō, nōlō (and in poetry some other verbs), may take a Perfect Infinitive instead of the Present; as,—
hōc jam prīdem factum esse oportuit, this ought long ago to have been done.