Are all systems of informal logic really just systems of formal logic that have not yet been understood mathematically?

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    You can see Formal and Informal Logic: “Does Informal Logic deal with the issues of the analysis and assessment of informal argument better than Formal Logic by avoiding translation to artificial formal languages and the use of mathematics?” Nov 20, 2017 at 7:51
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    Probably no, but much of this depends on your faith in formal logic's ability to translate and on what you think the fuzziness involved in a lot of human thinking is.
    – virmaior
    Nov 20, 2017 at 13:13
  • It seems to me that the phrase 'informal logic' is an oxymoron. So I'd say that informal logic is either unsystematic and unsound (thus not logic) or it can be formalised. But I'm no logician.
    – user20253
    Jan 20, 2018 at 12:13
  • Does it help to ask "how could you tell?" More specifically, how would you make the case that a claimed formalization of an informal logic is the 'correct' formalization of it?
    – sdenham
    Apr 20, 2018 at 3:42

1 Answer 1


It depends what you mean by "all systems of informal logic". If you mean all the ways people can reason, then your question is tantamount to asking if all human thinking can be formalized... and we simply don't know that. Even the lesser question whether all human thinking can be simulated by some machine is basically asking whether a strong AI can be built. (You can simulate what don't quite understand--for instance there's no deep way to understand an artificial neural network that [say] beats most people at Backgammon.)

If you mean just some system(s) of IL that people have (more or less vaguely) described... usually a FL based on that exists if the IL was interesting enough. (So take this as an experimental postulate.) Some 20th century examples (as the date of formalization): temporal & modal logic(s), paraconsistent logic(s) etc. The IL system may of course be flawed, but then it depends what is a logic, which is itself not a settled question even for the formal ones.


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