grammatical question! (maybe we should dedicate an ongoing thread to grammar?)

[cicero]

which is correct:
Dr Smith, together with his colleagues Dr Jones and Dr Why, *have* been working on purple cat research... (because the "been working" refers to all three)

or
Dr Smith, together with his colleagues Dr Jones and Dr Why, *has* been working on purple cat research... (because the colleagues are in a clause and the "been working" goes back to Dr. Smith)

[RingTailedLemur]

The second one, I think.

[zainabzks]

The second sentence is correct. Dr. Smith is the subject of the sentence. The verb should agree with him.

[Giggity]

Too many words. It sounds clunky. How about "Dr Smith, Dr Jones, and Dr Why have been working on purple cat research."

[southern girl]

Dr. Smith and his colleagues, Dr. Jones and Dr. Why, have been working on purple cat research.

[Thipu1]

Dr. Smith and his colleagues, Dr. Jones and Dr. Why, have been working on purple cat research.

I would word the sentence this way.  It's much smoother to read.

BTW, I would welcome a grammar thread.

[cicero]

thanks to all who responded.

I am editing this article and alas cannot really "touch" it (believe me, I would re-write the whole thing if I could...), but I have to correct *really bad errors". I can't really change the sentence around because the focus is on Dr. Smith.

(you wouldn't believe how touchy some people can get and I so do not want to get into WWIII)

[Hmmmmm]

The second one.  The subject is Dr. Smith.  The sentence is just clarifying he isn't doing it alone.  Think of it as someone introducing him before a speech he is giving. 

[Bijou]

Has.

[violinp]

I would write, "Drs. Jones, Smith, and Why have been working on purple cat research." It's simple and direct.

[bansidhe]

I would rephrase the sentence as other folks suggested, but here's a tip: in cases like the original sentence, remove the clause that modifies the subject. That will let you know which word is the correct choice.

Original sentence: "Dr Smith, together with his colleagues Dr Jones and Dr Why, have/has been working on purple cat research."

Clause removed: "Dr Smith has been working on purple cat research."

[Dindrane]

If the doctors were listed in the sentence (e.g. Dr. Smith, Dr. Jones, and Dr. Why), then the verb would need to be plural. In the sentence as written, the clause about Dr. Jones and Dr. Why is more similar to a parenthetical aside -- it's not really part of the subject. Therefore, the verb should be singular to match the singular subject (Dr. Smith).

If you think you might be able to get away with it, you could also rephrase the sentence to "Dr. Smith and his colleagues, Dr. Jones and Dr. Why, have been working on purple cat research." That makes the subject "Dr. Smith and his colleagues" and the part with their actual names is a clarifying aside separate from the subject. It keeps the emphasis on Dr. Smith, but it might read a little better.