Thomas Dalton wrote:
You should always cite the source you used, that's just common sense. I can't see how anyone could argue that it's appropriate to cite something you haven't looked at. Whether you should include that source's source as well probably depends on the circumstances.
This comes up in academic discussions now and then, and though most people theoretically agree with you, it's nonetheless quite common. In fact some researchers have tracked this sort of citing-via-an-intermediary by looking for the propagation of typos in citations, which is a fairly good (though not perfect) indicator that a citation was lifted from a previous citation. ;-)
It's particularly common (and not particularly strongly disliked) if all you're doing is crediting the originator of something, as in "we used some technique (Originator 1948)". In that case as long as you were correct that the original paper *was* the original paper, the citation is fine---and determining whether it was the original paper or not doesn't actually require reading it, and in fact simply reading it wouldn't be sufficient to determine that.
-Mark