In prehistoric times it was a major no-no to cheekily separate the particle ‘to’ from its infinitive verb. ‘Do not split the infinitive’ was the law of the land. ‘What in the world are you talking about?’ responds anyone born after 1960. In fact, since that time the rule has more or less been ignored.
And then came its death knell, on September 8, 1966:
Space: the final frontier. These are the voyages of the starship Enterprise. Its five-year mission: to explore strange new worlds, to seek out new life and new civilizations, to boldly go where no man has gone before. – Star Trek
There is no longer any controversy. There is nothing wrong with inserting a word between ‘to’ and ‘verb’. The problem is, most often the inserted word is the lowest of grammatical life forms, an adverb. The lowly adverb has flourished (despite ending in ‘-ly’, ‘lowly’ in this sentence is an adjective, and ‘adverb’ is a noun. Had to get that out there). Perhaps an adverb’s highest honor is to breezily insert itself into an otherwise mundane sentence.
An adverb’s highest honor is to breezily insert itself into an otherwise mundane sentence.
An adverb’s highest honor is to insert itself, breezily, into an otherwise mundane sentence.
What if we could do without adverbs altogether? The world would be a better place.
Inserted into an otherwise mundane sentence, the adverb felt mighty proud.
The adverb brightened the terminus of the otherwise mundane sentence.
It worked behind the scenes to buttress the verb’s presentation and eliminate the need for itself. This is an adverb’s highest honor.
. . .
The split infinitive is common in written (usually journalistic) english, not so common in spoken english. This is a clue to the limited value of adverbial insertion.
Here is a useful guide: don’t bother splitting an infinitive. But if you do, try to limit yourself to short adverbs (boldly, quickly, etc.). At all costs, in all situations, avoid the polysyllabic adverbs (especially increasingly).