An adjective in the comparative degree is often followed, not by a clause of degree as we should expect, but by an infinitive introduced by than; as, “He is wiser than to make such a remark.” The infinitive phrase modifies wiser and is joined to it by the subordinating conjunction than.
IV. In addition to the foregoing constructions we occasionally find the infinitive used as the object of a preposition. The few prepositions governing infinitives are except, but, and save, the two latter meaning except; as, “Make no expense but to do good to others or yourself.” Usually, to, the sign of the infinitive, is omitted after these prepositions.
In the following sentences the preposition governing an infinitive phrase is omitted.—“It’s worth quite a little fortune to any man who gets it, and I understand that there are more vacancies than there are men, so that the trustees are at their wits’ end what to do with the money.”—Conan Doyle. “I am somewhat at a loss what to think.” The prepositional phrases at their wits’ end and at a loss are complements of the verbs are and am, used instead of adjectives because there are no equivalent adjectives. The infinitive phrases answer the questions at their wits’ end about what? and at a loss about what? and so are best disposed of as objects of the preposition about understood.
Note.—In the construction, “I am about to go,” about is usually disposed of as a preposition governing the infinitive. Instead it should be considered as an adverb modifying the infinitive, which is the complement of am.
The preposition for may take a double object; thus, “A space was left between them for the garrison to pass out.” The answer to the question for what? is, the garrison to pass out. Such a prepositional phrase is often used as logical subject after the anticipative subject it; thus, “It is not lawful for us to put any man to death.”
Note.—In the common construction, “I cannot but think,” the word think is an infinitive with to omitted, used as object of the preposition but. There is an ellipsis in this construction which must be supplied for analysis, unless we dispose of the whole expression at once as an idiomatic verb-phrase. Supplying the ellipsis we have, “I cannot do anything but think.”
The expression, “I can but think” is best disposed of now as equivalent to “I can only think,” for that is what it signifies to us. The verb then is can think, and but is its adverbial modifier.
V. The infinitive may be used independently, having no grammatical relation to any other word in the sentence; thus, “To tell you the truth, my errand is not so much to buy as to borrow.”—George Eliot. Certain stereotyped phrases are used in this way, such as to be sure, to speak plainly, to make a long story short. They are useful to express in few words what in other more regular constructions it would take many words to say.
In this sentence of Hale’s, “This sort of vagueness, not to say misapprehension, affects the question, Who are our Leaders?” we have an independent infinitive phrase which adds much to the meaning of the sentence. It tells us here that the author uses the noun vagueness so as to be on the safe side, but in his opinion misapprehension is the more precise term.
Note.—An independent expression very similar to the one just given is found in the following sentence,—“It appeals to our more purely human, one might almost say domestic, qualities.”—Lowell.