§451. Infinitive Mood
The Infinitive is properly a noun denoting the action of the verb abstractly. It differs, however, from other abstract nouns in the following points: (1) it often admits the distinction of tense; (2) it is modified by adverbs, not by adjectives; (3) it governs the same case as its verb; (4) it is limited to special constructions.
The Latin Infinitive is the dative or locative case of such a noun1 and was originally used to denote Purpose; but it has in many constructions developed into a substitute for a finite verb. Hence the variety of its use.
In its use as a verb, the Infinitive may take a Subject Accusative (§ 397. e), originally the object of another verb on which the Infinitive depended. Thus iubeō tē valēre is literally I command you for being well (cf. substantive clauses, § 562. N.).
Infinitive as Noun
J. H. Allen and J. B. Greenough, New Latin Grammar (Boston: Ginn, 1903). Text provided under a CC BY-SA license by Perseus Digital Library, http://www.perseus.tufts.edu, with funding from the National Endowment for the Humanities.