SPLIT INFINITIVE • DICTIONARY ONE.COM • Definition of Split infinitive

... effort is marked by much sincerity and idealism, though in grammar and practicability it is less distinguished. We might mention the erroneous use of whom for who (a not uncommon defect amongst amateur writers), the faulty use of the word usurping where depriving is meant, and the split infinitive "to at least make;" all three of which mistakes occur on page 138. Mr. Ericson should drill himself more thoroughly in the principles of syntax. Other essays of this series are included in the present issue. "On Contentment" gives an illustration which we fear will injure ...

— Writings in the United Amateur, 1915-1922 • Howard Phillips Lovecraft

... of an infinitive it should not be separated from the other part by an adverb, as, "to hastily think," for hastily to think, or, to think hastily. Condemnation of the split infinitive is now pretty general, but it is only recently that any one seems to have thought of it. Our forefathers and we elder writers of this generation used it freely and without shame—perhaps because it had not a name, and our crime could ...

— Write It Right - A Little Blacklist of Literary Faults • Ambrose Bierce