Fastfission wrote:
It seems to me to fall back in part on the nature of the claim. "Interpretation" often crossed over into original research, but quoting can go both ways. If the quotes selected are used to illustrate a point which can be found in secondary literature, that seems fine to me (i.e., quoting directly from _Origin of Species_ to explain Darwin's thoughts on some point in a way which would not be controversial to anyone), but cherry-picking quotations or using quotations to support points not in secondary literature is original research (i.e. quoting directly from _Origin of Species_ to support your own, idiosyncratic and unorthodox interpretation).
If the source is published, quoting from it should be fine, as long as the point of the quoting is not problematic and one could ultimately find the same argument made about the source (implicitly or explicitly) in secondary literature.
It's hard to imagine a quotation from anywhere that isn't cherry-picked. Reviewing Darwin's work to differentiate between what was used in secondary literature, and what is an original usage is itself as much original research as the result. Either Darwin is a quotable author or he isn't; there's no point to creating a large amount of weasel room that would allow us to opt out when what he says does not conform to one's individual point of view.
Ec