The Personal Infinitive

The personal infinitive — or inflected infinitive — is a verb form that conjugates the infinitive for person and number, giving it endings that signal who performs the action: falar (“to speak”), but falarmos (“for us to speak”); partir (“to leave”), but partires (“for you to leave”). It is a feature Portuguese shares only with Galician and, in the wider panorama of the world’s languages, a striking rarity: a verb that, nominal and unspecified by nature, nonetheless agrees with a subject. Few phenomena identify Portuguese so quickly to a Romance philologist.

The forms

The personal infinitive is built from the impersonal infinitive by adding person endings. In the first and third persons singular it coincides with the plain infinitive; the remaining persons take distinctive endings.

eu	falar
tu	falares
ele/ela	falar
nós	falarmos
vós	falardes
eles/elas	falarem

The endings are invariable and apply to every conjugation, regular or irregular, with no change to the stem:

Person	Ending	falar	comer	partir
eu (I)	—	falar	comer	partir
tu (you)	-es	falares	comeres	partires
ele/ela (he/she)	—	falar	comer	partir
nós (we)	-mos	falarmos	comermos	partirmos
vós (you, pl.)	-des	falardes	comerdes	partirdes
eles/elas (they)	-em	falarem	comerem	partirem

Note that the nós form — falarmos [fɐˈlaɾmuʃ] , partirmos [pɐɾˈtiɾmuʃ] — is set apart from the plain infinitive by -mos, and that the eles form always ends in -em. The vós form (-des) is today literary or regional, like the pronoun itself.

When it is used

The golden rule is simple: the personal infinitive is used when the infinitive clause has its own subject, especially one different from the subject of the main clause. The inflection makes clear who is acting, with no need of a conjunction or a finite verb.

It is especially frequent after prepositions and phrases that introduce adverbial clauses — para (for/so that), por (because of), sem (without), até (until), ao (on/upon), depois de (after), antes de (before), apesar de (despite) — where the infinitive’s subject differs from the main one:

• Comprei estes livros para vocês lerem. — “I bought these books for you to read.”
• Ao entrarmos na sala, todos se calaram. — “On our entering the room, everyone fell silent.”
• Depois de as crianças adormecerem, saímos. — “After the children fell asleep, we went out.”
• Agradeço-vos por terdes vindo. — “I thank you for having come.”

When the infinitive’s subject is the same as the main verb’s and sits next to it, the impersonal infinitive usually suffices: queremos partir (“we want to leave”), not queremos partirmos. Inflection is required, however, whenever one wishes to mark the subject clearly, to give it emphasis, or when the verb form is far from its subject. Compare:

This possibility of alternation gives Portuguese a rare stylistic subtlety: often both forms are grammatical, and the choice to inflect or not expresses a nuance of focus and of personhood.

The look-alike: the future subjunctive

In regular verbs, the personal infinitive is identical to the future subjunctive: quando falarmos (“when we speak”), se partires (“if you leave”). The resemblance is only superficial. The two differ in syntax — the future subjunctive requires a conjunction such as se (if), quando (when) or logo que (as soon as) — and, decisively, in the morphology of irregular verbs, where the two paradigms diverge completely, because the future subjunctive is built on the preterite stem:

Person	Personal infinitive	Future subjunctive
eu	ser · fazer · ter	for · fizer · tiver
tu	seres · fazeres · teres	fores · fizeres · tiveres
nós	sermos · fazermos · termos	formos · fizermos · tivermos
eles	serem · fazerem · terem	forem · fizerem · tiverem

Thus para eles virem (personal infinitive of vir, “to come”) stands opposed to se eles vierem (future subjunctive). Telling the two apart is one of the keys to sound Portuguese verb morphology.

An exception that proves the rule

There is one context in which grammatical tradition advises against inflection even with a plural subject: after the causative verbs (mandar “to order”, deixar “to let”, fazer “to make”) and the verbs of perception (ver “to see”, ouvir “to hear”, sentir “to feel”), when these govern the infinitive directly. One says mandei-os sair (“I ordered them to leave”) and ouvi-as cantar (“I heard them sing”), not mandei-os sairem. Here the infinitive serves as the main verb’s complement, without a subject of its own, and so stays impersonal.

Where it comes from

The origin of the inflected infinitive is one of the most debated questions in Romance linguistics, for Latin had no equivalent form. Two explanations compete for the ground.

The first, phonetic in basis, derives the personal infinitive from the Latin imperfect subjunctive (amārem, amārēs, amāret, amārēmus, amārētis, amārent), whose endings correspond regularly to the Portuguese ones (-mus > -mos, -tis > -des, -nt > -m). This same origin would explain the formal merger, in regular verbs, with the future subjunctive.

The second, morphological in basis, sees the phenomenon as an innovation of Galician-Portuguese: an infinitive that, by analogy, took on the personal endings already present in the future subjunctive, then spread them across the whole paradigm. In its favour weighs the appearance of inflected infinitives in old Leonese texts, which points to an Ibero-Romance creation rather than a direct inheritance. Modern historical grammars tend to combine the two factors: an inherited formal base, reinterpreted and generalised by analogy.

A signature of the language

Whatever its genesis, the personal infinitive is today one of the most characteristically Portuguese features. Where Spanish, French or Italian resort to conjunctional clauses (para que nós saibamos, pour que nous sachions, “so that we may know”), Portuguese has an elegant economy: para sabermos. It allows infinitive clauses with their own clear, inflected subject, and lends Portuguese prose a syntactic fluency that translators from the other Romance languages often envy.