But each of these infinitives is also a verb,—for (1) it expresses action; (2) it may be modified by an adverb, as in No. 5; (3) it takes an object if it is transitive, as in No. 6.
An infinitive (as the examples show) has regularly no subject and therefore lacks both number and person. Hence it is not bound by the general rule for the agreement of a verb with its subject ([§ 222]). From this fact it derives its name, infinitive, which means “unrestricted” or “free from limitations.”[38]
310. The infinitive is a verb-form which partakes of the nature of a noun. It expresses action or state in the simplest possible way, without person or number.
It is commonly preceded by the preposition to, which is called the sign of the infinitive.
To is not, in strictness, a part of the infinitive, but it may be so regarded for convenience, since the infinitive, in most of its uses, is preceded by to.
Note. To sometimes stands for an infinitive in careless speech: as,—“You may go if you wish to” (that is, “if you wish to go”). Such expressions are to be avoided. It is better to say, “You may go if you wish.”
311. The infinitive often lacks to, especially in verb-phrases with the auxiliaries will, shall, may, can, must, might, could, would, should, do, did. For examples, see [pp. 102], [114], [124].
312. The infinitive has two tenses,—the present and the perfect.
1. The present infinitive is the verb in its simplest form, usually preceded by to: as,—to live, to teach, to bind, to strike.
2. The perfect infinitive is made by prefixing the infinitive of the auxiliary verb have to the past participle ([§ 243]): as,—to have lived, to have taught, to have bound, to have struck.