Grammar: Split Infinitives

What is a split infinitive, and why should I avoid using one?

This is a split infinitive:

To boldly go where no man has gone before!

The infinitive is to go, and it has been 'split' by the adverb boldly. Split infinitives have been the cause of much controversy among teachers and grammarians, but the notion that they are ungrammatical is simply a myth: in his famous book Modern English Usage, Henry Fowler listed them among 'superstitions'!

Split infinitives are frequently poor style, but they are not strictly bad grammar. In the example above, to avoid the split infinitive would result either in weakness (to go boldly) or over-formality (boldly to go): either would ruin the rhythmic force and rhetorical pattern of the original. It is probably good practice to avoid split infinitives in formal writing, but clumsy attempts to avoid them simply by shuffling adverbs about can create far worse sentences.

And so, in my opinion, it's up to the writer and his or her style.

Source: Here