Where an adverb or _each_ goes
Some words can sit in several places in a sentence without making it ungrammatical, and each place says something slightly different. Where each goes decides how a sentence flows and what it emphasises, where an adverb goes is a trade-off between the unit it modifies and the unit it emphasises, and a split infinitive is one of the positions an adverb can take.
Where each goes
Each is used adjectivally, as in Each ward has 25 beds, and as a pronoun, as in The hospitals have 10 wards each, The hospitals each have 10 wards or Each of the hospitals have 10 wards. Used adjectivally it immediately precedes the noun it modifies, as is almost always the case in English — each patient on the ward, defibrillators on each ward. Used as a pronoun it usually indicates that several groups or factors had the same number of characteristics, and the main problem is where to position it in the sentence or whether to express the idea differently; there is no single answer to this.
That nausea and headache were the most common treatment-emergent adverse events (TEAEs), each in 12% of patients, can be written in several ways. Putting each in 12% of patients in brackets cannot be misunderstood, since it can only mean that 12% had nausea and 12% had headache, but it puts important information, that it was 12%, in brackets. Placing each before the prepositional phrase, after a comma, is not misunderstood either and no longer deemphasises the 12%, but the position of each interrupts the flow of the sentence. Placing it at the end, in 12% of patients each, is also clear, flows well and avoids the comma needed if each comes before in. Repeating (in) 12% after each event avoids the problem with each but is cumbersome. Nausea and headache (both [in] 12%) avoids it elegantly by using both. Putting each before the two symptoms, 12% of patients each had nausea and headache, is not incorrect, but it is disturbing, although the meaning will still be understood. Repeating the figure outright, 12% had nausea and 12% had headache, is a little cumbersome when the numbers are identical, but not when they differ, as in 12% had nausea and 10% had headache, and this is how to avoid each and both when you are not sure where to position them. With three or more events, such as nausea, vomiting and headache, the constructions with brackets, with a comma, with each at the end, with the repeated (in) 12% and with both are built the same way, with all in place of both.
Exactly how to deal with this is a matter of personal style and preference. One experienced writer prefers each at the end or the solution with both, and, because the sentence is about what was most common, prefers to make that the subject in both cases: The most common TEAEs were nausea and headache in 12% of patients each, or The most common TEAEs were nausea and headache, both in 12% of patients.
Specificity and emphasis in placing an adverb
Adverb placement is complicated by the variety and abundance of syntactic units an adverb can modify, ranging from words to phrases to sentences, the most likely being verbs and verbals, adjectives and adjectivals, and other adverbs. Another complication is the inherent mobility of adverbs within a sentence. Two reasons guide the placement: specificity, which is selecting the exact syntactic unit the adverb modifies, and emphasis, which is selecting the syntactic unit to be emphasised.
It would be a simple process if an adverb were placed before the most specific syntactic unit, but selection is also based on emphasis, for example before the main verb of a predicate. The range of placement possibilities also increases with the type of adverb: manner, negation, degree, time. A classic example of emphasis over specificity is I only have eyes for you rather than the more specific I have eyes only for you.
In Halothane was substituted for ether lightly to anesthetise rats used in this study, the infinitive phrase is the most specific unit the adverb modifies. Logic rules out the verb phrase was substituted as the modified unit, because was lightly substituted is illogical. Lightly to anesthetise is logical, but the back-modification, or squinting modification, for ether lightly is possible: lightly seems to back-modify for ether and premodify to anesthetise at once, and the meaning substituted for ether lightly is unintended. To avoid the mismodification, the revision places lightly between the infinitive marker to and the infinitive anesthetise, to lightly anesthetise, so that it modifies the infinitive phrase exclusively. Grammatical folklore has stigmatised splitting an infinitive, but avoiding a split infinitive can result in the modification of an unintended unit. Splitting the infinitive is a misnomer, because the infinitive is the base form of the verb, here anesthetise, and to is its marker, so the split is between the marker and the infinitive, a split of the infinitive phrase. Lightly, a manner adverb, is more mobility-limited than a degree adverb and a time adverb, as shown by its being unable to modify from the front or the end of the sentence.
In Treatment of HT-4 cells with various tocopherol analogues protected cells completely against glutamate-induced cytotoxicity, the adverb stands before the specific unit against glutamate-induced cytotoxicity, yet placement before the main verb, completely protected, may be preferred. The choice of position may then be more a function of the intended emphasis of the verb than of modifying the most specific unit; another perspective is to take the verb protected with the prepositional phrase after it as the unit the adverb modifies. Placing completely at the end of the sentence, after a comma, emphasises it by position and by comma segregation. Completely would be illogical at the front of the sentence, possibly because a degree adverb must be close to the unit it modifies.
In All large-scale testing methods were capable of simulating successfully the earthquake response, the adverb usually precedes rather than follows the unit it modifies, capable of successfully simulating, which splits the preposition-verb phrase in the same way as an infinitive phrase is split. Simulating is a gerund, a present participle functioning as the object of the preposition of, and adverbial modification is still appropriate because its verb-like structure classifies it as a verbal. Placing the adverb before the linking verb, successfully were capable, is an unconventional pattern, while placing it before the adjective, were successfully capable, is possible. It appears that where the main verb is a linking verb, placement before the most specific unit is preferred to placement before the main verb. End-of-sentence placement after a comma is logical, and the position and the comma emphasise the adverb, whereas front-of-sentence placement would be illogical, probably because of the distance from simulating and the movement limitations of a manner adverb.
In A variety of techniques recently have been developed in this new discipline, the auxiliary verbs have and been before the main verb developed complicate placement, but the adverb can simply be placed before the main verb, have been recently developed. The meaning seems to be the same as with recently before have or between have and been, and one reason for the lack of any overt difference may be the flexibility of recently as a time adverb. That flexibility shows in its placement at the end of the sentence after a comma and at the beginning of the sentence, and placement after developed is also possible. The choice between the front and the end of the sentence may depend on the requirements of paragraphing, that is, on how the sentence relates to the sentences around it.
The split infinitive
In the early twentieth century, some stylebook authors would have objected to "to boldly go where no man has gone before" because the adverb boldly stands between to and go. In 1908, H. W. Fowler argued that the split infinitive is an ugly thing, but one among several hundred ugly things, while the sixteenth edition of the Chicago Manual of Style states that it is now widely acknowledged that adverbs sometimes justifiably separate an infinitive's to from its principal verb. An English infinitive is made up of two separate pieces, an infinitive marker, to, and the stem of the verb. One medical editor argues that an adverb that modifies the infinitive can be tucked between them, and that good writers do it all the time. In that editor's view, the meaning of "to boldly go" is clear, and the alternative phrasings sound clumsy. A good writer would avoid putting too many words between the infinitive marker and the stem, but a single adverb can fit there nicely.
Placing an adverb within an infinitive, as in to quickly determine, was disallowed in the past. A guide for nonnative English speakers holds that nowadays an infinitive may be split where there is good reason to place the main emphasis on the nature of the action, as in to randomly allocate patients to treatment groups. In most situations, however, the guide holds that placing the adverb after the verb is still the safer ground. It advises keeping adverbs close to the verb to avoid confusion.