Proof by contrapositive = modus tollens?

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SUMMARY

Proof by contrapositive and modus tollens are distinct logical concepts, despite common misconceptions. Modus tollens operates under the assumption that the implication "If p, then q" is valid, allowing for the conclusion that if q is false, then p must also be false. In contrast, proof by contrapositive does not assume the validity of the implication but instead derives the contrapositive by assuming not q to conclude not p. This nuanced understanding clarifies the differences between these two logical methods.

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Ryker
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I was just looking at the http://en.wikipedia.org/wiki/Modus_tollens" and found the line "Modus tollens is sometimes confused with proof by contradiction or proof by contrapositive." I thought proof by contrapositive and modus tollens are one and the same though. Is that then not the case or is Wikipedia wrong?
 
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I'm not too sure on this, but it seems to be it may just be a logical nuance.

In Modus tollens proper, I believe (If p, then q), is made as an assumption. Or another way, I think the validity of the statement If p then q is already assumed in Modus tollens.
Versus when performing a proof by contrapositive, we don't know that the statement (If p then q) is actually valid, so we proceed to try to derive q after assuming only p. (We can't assume the entire implication to perform a proof, there would be nothing to prove.) Proof by Contrapositive we assume not q and then derive not p.

Did any of that make sense or did I just make up a whole bunch of stuff?
 
Yeah, it does make sense, quite a bit actually. Thanks!
 

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