Infinitives
Latin has temporal infinitives. For example, you can express having-done-verb with a single word (e.g. portavisse, to have carried) or being-about-to-do-verb with almost a single word (e.g. portaturus, about to carry, or the more famous morituri, those who are about to die, or those who will die, which is to say everyone).
Portuguese has personal infinitives. For example, you can express for-us-to-do-verb with a single word (e.g. perguntarmos, for us to ask) or for-them-to-do-verb with a single word (e.g. perguntarem, for them to ask).
One of the many ways in which these infinitives are useful is in predicating qualities of them. For example, you can say concisely in Latin that it is good to have gone swimming or it is exciting to be about to eat or it is difficult to be about to write something or it is better to have loved and to have lost than never to have loved at all (my guess is melius est amavisse et perdisse quam numquam amavisse) or even the corresponding it is better to be about to love and to lose than never to be about to love (melius est amaturus et perditurus esse quam numquam amaturus esse). And you can say concisely in Portuguese that it is sad for us not to be able to help (é triste não podermos ajudar, where "for us not to be able" is conveyed by não podermos).
What's interesting is that Portuguese has no temporal infinitives and Latin has no personal infinitives. You can see this easily by contrasting reference books like Barron's 501 Latin Verbs Fully Conjugated in All the Tenses (Prior and Wohlberg) and 501 Portuguese Verbs Fully Conjugated in All the Tenses (Nitti and Ferreira). The grammatical categories are simply different.
It would be fun to have both features available in a single language, so that we could form temporal personal infinitives by some means of grammatical inflection. For example, we would be able to have a single word for my having gone or their being about to eat or our having studied or your being about to read. Is there any language that can do this? Neither Portuguese or Latin is up to the task.
There is actually another grammatical feature that Latin infinitives can convey -- voice (active or passive). A Latin infinitive can also refer to the state of experiencing an action, as opposed to engaging in the action, and this is true for past infinitives as well as present infinitives. Most Latin verbs can form five different infinitives (amare, to love [now, or in general]; amari, to be loved [now, or in general]; amavisse, to have loved [in the past], amatus esse, to have been loved [in the past], amaturus esse, to be about to love [in the future]). Some authorities also suggest the future passive infinitive amatus iri, to be about to be loved [in the future]. I have never used this form or seen it in a text, but I have no doubt that it's attested.
Thus, Latin infinitives and Portuguese infinitives both support different kinds of inflection along different dimensions akin to the regular inflection of finite verbs. They both suggest a general pattern where we can move from a finite verb form that expresses a tense, mood, voice, person, and number to an infinitive conveying the notion of "for this to happen" or "the idea or fact of this happening". In Latin, the allowable dimensions of this parallelism are limited to tense and voice; in Portuguese, they are person and number. (Nitpicking: those Latin infinitives that rely on participles also indirectly express number, and arguably gender, which is not otherwise marked in Latin verb inflection: amatus esse and amati esse; amaturus esse and amaturi esse. Latin infinitives that do not rely on participles never express number.) Neither language allows subjunctive infinitives, which seems to be OK because you can often get a subjunctive effect where strictly necessary by using a subjunctive of the verb to be (or, in Portuguese, sometimes a subjunctive and sometimes a conditional).
So a larger question might be whether there is any inflected language with a regular process for making infinitives (or other nouns -- or, for that matter, participles, which could be the subject of a whole other post in themselves) out of any arbitrary finite verb. Latin and Portuguese, taken together, offer tantalizing hints in that direction, but neither one quite goes there.
