Don’t apply for a Ph.D. program and hope to defer an acceptance you receive. It’s not like undergraduate acceptance. If you don’t take the offer, you will have to reapply–in all but the most extraordinary circumstances. (One of my correspondents, at a major school in the eastern United States, says he has seen that once in seventeen years. Another friend, at another major school who previously taught at a midwestern American powerhouse, says he’s never seen it at all.)
I didn’t ask my correspondents a follow-up question I should have asked them: Would it actually count against you to refuse to accept an offer and then apply the next year? I could see it argued both ways, so I won’t speculate.
One more thing. I did hear from a senior professor who has held posts at two of America’s top universities that a student who has applied, is turned down, and then applies again the next year does indeed have a strike–or two–against him or her. He didn’t presume to speak for every school everywhere, of course, but he did seem to think this was the way it was commonly done, and he is very widely connected.
So by all means apply, friends, but only when you’re ready to give it your best shot.
UPDATE April 2012: I have encountered several very good Ph.D. programs in the U.K. that do, in fact, let you defer your acceptance for a year. Since few of them offer non-Brits any money, I can see why they can afford to do that, since many of them need non-Brits to keep functioning, so they really have to be a bit flexible about letting you line up your scholarships from elsewhere. My column was written in the context I know best, namely, North American programs that do give significant funding and therefore generally are quite particular about you applying and then either taking the offer or starting fresh the next year.