For anyone who may not have been persuaded, or convinced, by my railing against the Associated Press Stylebook's idiotic "split verb" rule yesterday, I offer some helpful citations:
From The New York Times Manual of Style and Usage: In fluid writing, an adverb used with a compound verb should normally be placed between parts of the verb (the way normally is, a few words back in this sentence, and the way usually is, in the next example): He will usually take the opposing side. A similar rule applies when a verb like is links a noun to its modifier Refundable fares are often expensive (not often are expensive).
From Garner's Modern English Usage (fourth edition): Many writers fall into awkward, unidiomatic sentences when they misguidedly avoid splitting up verb phrases. Although most authorities squarely say that the best place for the adverb is in the midst of the verb phrase, many writers nevertheless harbor a misplaced aversion, probably because they confuse a split verb phrase with the SPLIT INFINITIVE. H.W. Fowler explained long ago what writers still have problems understanding: "When an adverb is to be used with [a compound] verb, its normal place is between the auxiliary (or sometimes the first auxiliary if there are two or more) and the rest. Not only is there no objection to thus splitting a compound verb … but any other position for the adverb requires justification."
From Merriam-Webster's Dictionary of English Usage: Copperud 1970, 1980 talks about an erroneous idea widespread among newspaper journalists that adverbs should not separate auxiliaries from their main verbs (as in "you can easily see" or "they must be heartily congratulated"). The bugaboo, commentators agree, seems to have spring from fear of the dread split infinitive. … Copperud cites five commentators on the subject, all of whom see no harm in placing an adverb between the parts of the verb, and one of whom (Fowler 1965) prescribes such placement. … Since dividing the auxiliary from the verb with an adverb has been approved at least since Lindley Murray 1795, it would seem that Fowler is justified in calling the avoidance a superstition.
From Fowler's Dictionary of Modern English Usage (Butterfield, 2015): The placement of adverbs in clauses and sentences follows standard rules, e.g. (a) (between auxiliaries) a car dealer who could certainly have afforded to hire somebody; (b) (between an auxiliary and a main verb) Roosevelt's financial policy was roundly criticized in 1933; he had inadvertently joined a lonely-hearts club. …
A bugaboo, a superstition, an error widespread among newspaper journalists, long sanctified by the AP Stylebook. Dump it.