Does the word "therefore" always require a comma if it is in the middle of the sentence? [duplicate]

Should you always type a comma after "therefore","however" etc. in the beginning of a sentence? Also, when these (and similar) words are used in the middle of a sentence, should there be a comma or semi-colon before and after the word?

Therefore, he must be killed!

That man is revolting, however, some find him attractive.

Sorry for the lousy examples. I couldn't think of any better.

Solution 1:

Not really. There are many cases for which a comma is unnecessary.

He is strong, and therefore a likely candidate.

However strong he is, he is not a likely candidate.

And so on.

As for subordinate clauses, where the words function as subordinating conjunctions, the comma isn't always necessary either.

He is strong, therefore he must be a likely candidate.

Still, I would use one with however in that case:

He is strong; however, I don't think he's a likely candidate.

Note the semicolon. A period would work there as well. This is because "however" doesn't really work as a subordinating conjunction. Therefore isn't usually classed as such either, but I believe it can function as one just fine.

Solution 2:

This is a problematic area, because the modern tendency is to omit commas wherever this can be done without prejudicing meaning and/or readability.

By their very nature grammars and style guides tend to be somewhat behind the times. Who can say whether I 'should' have inserted a comma after nature in the preceding sentence?

I suggest that as a rule of thumb, if you can reasonably speak the sentence without a noticeable pause after the word however, don't bother with the comma. Otherwise, use it (same rule applies to otherwise, obviously, but these things are never cut-and-dried).

Solution 3:

I found this here (ncsu.edu).

Chicago Manual of Style 5.69: "When [transitional adverbs] are used in such a way that there is no real break in continuity and no call for any pause in reading, commas should be omitted.

Chicago gives four examples: (1) The storehouse was indeed empty; (2) I therefore urge you all to remain loyal; (3) Wilcox was perhaps a bit too hasty in his judgment; (4) Palmerson was in fact the chairman of the committee.