Post History
You cite the (or a) source that you used. If you read it in Book A and that book says it came from Book B, you cite Book A because that's your source. If you choose to follow the reference and se...
Answer
#3: Attribution notice added
Source: https://writers.stackexchange.com/a/16911 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/
#2: Initial revision
You cite the (or _a_) source that _you used_. If you read it in Book A and that book says it came from Book B, you cite Book A because that's your source. If you choose to follow the reference and see it in Book B yourself, then you could cite either A or B (you used both). In that kind of situation, it's generally best to cite the source that's closest to _the_ source -- why cite A who cites B if you can cite B directly? Why shouldn't you cite B if you read it in A and you think A is reliable? Well, partly because sometimes sources get it wrong -- B might not really say what A says it does. But, more broadly, any author who's found to do this sort of thing -- citing a source that he didn't actually verify directly -- calls into question _all_ of his citations. If you think A is reliable then either (a) your readers probably do too, so citing A means something, or (b) you can explain why A is reliable.