A practical english grammar - Vyssaja skola 1978
Parenthetical adverbs
Sound symbols
Adverbs are used not only to modify elements within the sentence (they are called integral in that case); they are also used to express comments by the speaker (or writer) on the sentence as a whole (in which case they are parenthetical). When parenthetical adverbs are in initial or final position, there are usually pauses before or after them, and commas are used in writing. When they are medial, there are usually no pauses.
Parenthetical adverbs behave slightly differently in medial position from integral adverbs. Integral adverbs modify what follows them, and in negative sentences they follow n’t or not, since the adverb is part of the predicate and is negated, along with everything else, by the negative element.
We usually have breakfast in the dining room.
We don’t usually have it in the kitchen.
“Usually have it in the kitchen” is negated by the preceding don’t.
If we replace usually by obviously, a parenthetical adverb not stating something about the frequency of occurrence of what follows but stating the speaker’s attitude toward the information contained in the sentence, we find that in the affirmative sentence, it occupies the same position.
We obviously have breakfast in the dining room. (Who could possibly think otherwise?)
In the negative, however, we can not put obviously after don’t, since then it becomes negated along with the rest of the predicate. What we want to say is that we don’t have breakfast in the kitchen and that this fact is so obvious that it hardly needs to be said. Accordingly, the word order in this case is:
We obviously don’t have breakfast in the kitchen.
In case some auxiliary other than do occurs, the parenthetical adverb may come between the auxiliary and not.
We will obviously not stay here very long.
He is obviously not suited for the job.
If we say “He is not obviously suited for the job,” we mean that he is suited for the job, but in ways that are not obvious.
Of course can occur in any of the three adverbial positions. When it is medial, there are no pauses before or after it, although in writing it is commonly set off by commas by many writers.
Of course, this will not be necessary if you pay cash.
This will of course not be necessary if you pay cash.
This will not be necessary, of course, if you pay cash.
Naturally, obviously, clearly, certainly, etc., can also occur in any of the three positions, but they are avoided in medial position when an ambiguity might result from their being interpreted as integral rather than parenthetical adverbs.
Naturally, I was delighted by the news, (not: I was naturally delighted by the news.)
It was certainly a pity that you missed the meeting.
Enough is often combined with parenthetical adverbs to add a note of ironic emphasis.
Oddly enough, he refused a second piece of pie.
Doubtless (note the absence of -ly) and probably are used in medial position.
This will doubtless (probably) be no surprise to you.
They have doubtless (probably) left the city already.
Parenthetical adverbs can occur almost anywhere in the sentence if, in speech, there are pauses before and after or, in writing, there is punctuation.
She doesn’t—obviously—like him very much.
He turned down—oddly enough—our offer.