(c) As complement of an intransitive verb; as, “The art of reading is to skip judiciously.”—Hamerton. “For a long time the house has been to let.”—Barrie. The infinitive is plainly a completing term in both cases, but in the first it denotes identity with the subject, hence has the use of a noun complement; while in the second it tells the condition of the house, like the word vacant, and hence has the use of a predicate adjective. Sometimes it is possible to change the infinitive to an equivalent adjective; as, “The accident is to be deplored,” or, “is deplorable.”
Seem and appear as well as forms of the verb be are followed by this adjective infinitive. It is especially useful in denoting an action that is to take place in the future; thus, “He is to come soon.”
Note.—Some of the difficulty in disposing of infinitives is due to an attempt to speak of them in terms that apply to certain parts of speech. Sometimes this seems forced. For instance, in the sentence, “He seemed to tremble,” pupils are told to consider the infinitive as a predicate adjective, when it does not seem to them to bear much resemblance to an adjective.
What the pupils must see is this,—that to tremble completes seem and tells something about the subject he. The following sentences may be given,—“He seems a coward,” “He seems afraid,” “He seems to tremble.” The verb in each case has a subjective complement, but in one case this complement is a noun, in another an adjective, in another an infinitive, the choice depending wholly on the special meaning to be brought out. If the use of to tremble seems to the pupil sufficiently like that of afraid to warrant his calling it a predicate adjective, let him do so. If not, let him not try to name it, but say of it instead that it completes the verb and tells something about the subject.
The infinitive complement of a passive verb belongs here; for example, “The human voice may be made to attain a wondrous strength and richness of tone.”—Brook. This construction often arises from changing a sentence containing a double object into the passive form. In the active voice the sentence just quoted reads,—“We may make the human voice attain a wondrous strength, etc.” Notice that the passive construction has the advantage over the active in this respect, that it enables us to avoid telling who makes. This is especially convenient with the verb say. In the sentence, “He was said to have stolen the money,” no one is charged with having said that he stole.
Note.—The familiar expressions, “That is to say,” “It came to pass,” “I came to know him,” also belong here; came is used in the sense of became.
3. As an adverbial modifier of the verb. The infinitive is very often joined to a verb to denote purpose; as, “The salmon winters in the ocean, but in spring ascends the fresh water rivers to spawn, or lay its eggs.” Sometimes this infinitive is introduced by so as or in order. It has almost entirely displaced the adverbial clause of purpose.
The infinitive may also denote the result of an action; as, “His half worn shoes would wait until his small brother grew to fit them.”—Holmes.
In the following sentence from Barrie, “Leeby returned panting to say that the doctor might be expected in an hour,” the infinitive seems to be employed instead of another finite verb, for the meaning is not that Leeby returned in order to say, but rather that Leeby returned and said. In the sentence, He went home only to die, the infinitive denotes neither the purpose nor the result of his going home, but only a subsequent action. It might be preferable in such cases to call the infinitive an accompaniment of the verb rather than a modifier.
In this sentence from Holmes, “I grieve to say it, but our people, I think, have not generally agreeable voices,” to say it denotes the cause of my grieving.