"This should perfectly be done". "This should be perfectly done". Of the two sentences, which one is correct? I am confused about placing of adverb "perfectly". Should the adverb be placed before "be" or after "be". Or, could it be placed at either place?
Different kinds of adverbs work differently. "Perfectly" is a manner adverb: "The manner in which this is done should be perfect." According to the classification given in McCawley's The Syntactic Phenomena of English, manner adverbs are verb phrase (or V-bar) modifiers. They can ordinarily come after the verb phrase they modify:
This should [VP [VP be done] perfectly]
Other types of adverbs are ordered differently. Sentence adverbs like "probably", for instance, can come before the sentence they modify, or before or after the subject or an auxiliary of that sentence. Sentence finally, they need to be set off by a comma:
[S Probably [S this should be done] ]
and contrasting "probably" with "perfectly":
*Perfectly this should be done.
This *perfectly/probably should be done.
This should *perfectly/probably be done.
This should be done perfectly/*probably.
The last example with "*probably" is to be read with no pause before the "probably".
Both versions are correct (and archaic, not in common use) but
"This should be perfectly done".
sounds much more fluent and poetic. Both sentences have the same meaning though: the doing of this action should be perfect.
This is similar to the way we say:
"Didn't you eat a banana yesterday?"
We know [didn't] = [did not] so if we replace didn't with did not, we get:
"Did not you eat a banana yesterday?"
which is very old English. Today, we would say:
"Did you not eat a banana yesterday?"
If I was to suggest an alternative that sounds much more contemporary and is far more common than both of these, I would use
"This should be done perfectly".