Here are a few rules that may help you. 1. It is correct to separate two INDEPENDENT CLAUSES with a comma and a conjunction, like “but.” So, sentence #1 is correct. 2. If the the two independent clauses are short, like in your examples, most people think it is OK to leave out the comma, as long as your meaning remains clear. So, sentence #2 is also correct. 3. To be an independent clause, the clause must have both its own subject and its own verb. In your examples #3 and #4, “but lacks vision” does not have its own subject, but rather shares the subject “he” from earlier in the sentence. Thus, the first rule above does not apply. So, sentence # 3 is correct but sentence #4 is incorrect. 4. Each of your sentences would be better if they used a consistent tense: (“was” and “lacked”) or (“is” and “lacks”).

All are correct but #1's comma is a dramatic pause for the emphasis on "he". #3 is a matter of fact. #4, the comma is unnecessary. I am from the old school that believes that unnecessary things are considered baggage. Others may differ from me.

Numbers 1 and 4 are the most correct. But there is no space between the word and the comma.

(1) He was a good manager, but he lacks vision. (4) He was a good manager, but lacks vision. (2) and (3) would make more sense if you changed "lacks" to "lacked," so it would look like this: "he was a good manager but (he) lacked vision," with the (he) being an optional addition to the sentence.

thank you (: