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Michael Hardy
Michael Hardy
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A book on logic whose title and the identity of whose author escape me at the moment said that not all proofs by contradiction are indirect proofs. The idea is that when proving an inherently negative statement---one that asserts non-existence of something---one can proceed only by contradiction, which in that case constitutes a direct proof. I'll see if I can find it.

PS: When I wrote this I probably had in mind Inexhaustibility: a non-exhaustive treatment by Torkel Franzén, page 101.

A book on logic whose title and the identity of whose author escape me at the moment said that not all proofs by contradiction are indirect proofs. The idea is that when proving an inherently negative statement---one that asserts non-existence of something---one can proceed only by contradiction, which in that case constitutes a direct proof. I'll see if I can find it.

A book on logic whose title and the identity of whose author escape me at the moment said that not all proofs by contradiction are indirect proofs. The idea is that when proving an inherently negative statement---one that asserts non-existence of something---one can proceed only by contradiction, which in that case constitutes a direct proof. I'll see if I can find it.

PS: When I wrote this I probably had in mind Inexhaustibility: a non-exhaustive treatment by Torkel Franzén, page 101.

Source Link
Michael Hardy
Michael Hardy
  • 1
  • 12
  • 85
  • 126

A book on logic whose title and the identity of whose author escape me at the moment said that not all proofs by contradiction are indirect proofs. The idea is that when proving an inherently negative statement---one that asserts non-existence of something---one can proceed only by contradiction, which in that case constitutes a direct proof. I'll see if I can find it.