Talk:Contraposition

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Mathematics High‑priority

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Philosophy: Logic Mid‑importance

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Archive 1

"Proof by contrapositive"

I have archived the previous discussions simply because they were all 4 years old or older. But I want to discuss something that was already brought up in those, namely mergers, since Wikipedia has many pages on the same topics. I want to start by merging Proof by contrapositive here, since it is a short article on a topic that relates very closely to this one. What do people think? Thiagovscoelho (talk) 11:47, 20 April 2024 (UTC)

Update: This merger has been performed. Thiagovscoelho (talk) 11:17, 30 April 2024 (UTC)

"Contraposition (traditional logic)"

I think it would also be good to merge Contraposition (traditional logic) here. The pages are closely connected. If this page covers contraposition in nonclassical logics, it should cover contraposition in traditional logic too. The material in the other page is very short and could be a section here. Thiagovscoelho (talk) 11:33, 30 April 2024 (UTC)

Update: This merger has been performed. Thiagovscoelho (talk) 00:29, 16 May 2024 (UTC)

Biconditional definition is ambiguous

I found that at Contraposition#Examples, it is claimed that :

"Since the statement and the converse are both true, it is called a biconditional", and further below it is also claimed that,
"If a statement (or its contrapositive) and the inverse (or the converse) are both true or both false, then it is known as a logical biconditional.".

I agree with the first claim. Then my interpretation of the second phrase is "If a statement and the inverse are both true or false then it is know as a logical biconditional", which is wrong because the definition of equivalence is "A -> B (the original statement) and B -> A (the converse)".

I don't see why the thruth values are being specified. May be my interpretation is wrong ? Oversleep9 (talk) 12:36, 13 August 2025 (UTC)

Proposed merger

The result of the discussion was not merged. FaviFake (talk) 13:03, 18 October 2025 (UTC)

The following discussion is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.

This article and the article on De Morgan's law appear to cover the same ground. Should we merge them? Marnanel (talk) 16:11, 3 September 2025 (UTC)

No. There isn't much in common. Contraposition is concerned with an inferential relationship between conditionals. De Morgan is concerned with duality relationships between and/or, between all/exists and between necessary/possible. Dezaxa (talk) 06:03, 24 September 2025 (UTC)

Disagree. While many of the low-level concepts are the same, De Morgan's laws are discussed specifically in the context of Boolean logic in computation. Contraposition is more of a philosophical concept. It would be like merging the pages for Fourier transform and Frequency domain: they are very closely related, but are discussed in different contexts that would make them inappropriate to merge. Nawor3565 (talk) 16:19, 10 October 2025 (UTC)

Strongly agree with Nawor. }:) 71.229.185.228 (talk) 21:23, 14 October 2025 (UTC)

The discussion above is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.

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