I was wondering why almost every other first-order-logic question refer to fitch style deduction? What is so different about fitch-style deduction that it has to be specified?


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    Standard undergraduate introduction into logic textbook I suppose... – Philip Klöcking Nov 27 '18 at 8:58
  • @PhilipKlöcking Suppose too, I guess. – Bertrand Wittgenstein's Ghost Nov 27 '18 at 9:19
  • @PhilipKlöcking But why specify "fitch-proof"? Does he prove it differently than other natural deduction systems? – Bertrand Wittgenstein's Ghost Nov 27 '18 at 9:22
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    I think you are right in questioning this particular tag. It should by a synonym of Fitch or omitted completely. – Philip Klöcking Nov 27 '18 at 9:49
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    I agree that the answer is definitely that it's ubiquitous in intro textbooks and intro classes, so we get a lot of questions that use it. But I don't think this makes sense as a question for meta, right? Like "why is fitch so popular" isn't a meta question about the site that can be discussed to better improve the site in any way. However the question of what to do with the fitch tag, rolling it into natural deduction or whatever else, I think is a good question. – Not_Here Nov 28 '18 at 1:06
  • @Not_Here You are correct, i thought it was a catchy title hence I put it. I mean is there any point in specifying "fitch-proof". I am speaking of experience, for a while I avoided answering question with fitch tag out of fear that I might confuse a questioner in case my natural deduction is different than fitch's. However, after looking at a bunch of questions and answers I realized it is just like any other natural deduction. – Bertrand Wittgenstein's Ghost Nov 28 '18 at 1:14

There is a software product from OpenProof Courseware called "Fitch" that goes with the Language, Proof and Logic textbook that appears to be what some people are referring to: https://ggweb.gradegrinder.net/support/manual/fitch Some of these questioners may be seeking help with this particular software product.

There is also a Fitch-style proof checker that I like to use that goes with the forall x textbook: http://proofs.openlogicproject.org/

However, the Fitch notation is an indented way to display subproofs in a natural deduction proof that was used by Frederic Brenton Fitch in his Symbolic Logic, 1952. Here is an illustration of the notation: https://en.wikipedia.org/wiki/Fitch_notation

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