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In Logic by Wifred Hodges he says

[..] you must rely on your common sense - as always in logical analysis.

So i'm confused (again!). What has common sense to do with logical reasoning? My previous understanding is that logical was an objective discipline. So it seems odd that the subjective and vague 'common sense' is in the logical mix. Certainly with the boolean logic of computer programming that I am more familiar with common sense has no role. Well I think it doesn't but then clearly logic isn't what I thought it was.

So what role does common sense play in logic? Does it really have an element of subjectivity?

Many thanks for any/all thoughts

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    Common-sense is the root of the sciences, the arts & philosophy. Logic didn't begat logic, that would be circular. But the sense that is common to us did - as by its nature it is inate. – Mozibur Ullah May 17 '14 at 18:07
  • The logic described by Aristotle is common-sense. He did not invent it but formalised ordinary practice. It is, after all, common sense to think 'logically' and the dialectic is what we usually use. His three laws are literally common sense. Are you sure you're right to say that common sense is not objective where logic is? I'd say this is not the case. – PeterJ Oct 29 '18 at 12:43
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I think that what Hodges means is that most of the basic principles of logic are based on our (human) linguistic and thinking habits.

Thus, the "ground" for some rules like :

"if a and b, then a"

and

"if a, then a or b"

can be found in the "usual" way we speak.

Tarski's Truth Definitions, one of the basic discovery of modern mathematical logic, can be read as a vindication of common sense view of truth : a linguistica assertion is true exactly when the facts "out there" are as the assertion says they are.

We can read Hodges' statement as a search for a "third way" between the theory about the a priori nature of logic (which is challenged by modern proliferation of "logics" : see Paraconsistent Logic and that asserting its conventional status.

  • +1 thank you for that. Apologies if this is very basic but are you saying that logic depends on (human) linguistics. So an alternative linguistic system would have different logic? I thought previous that logic was just 'out there' a priori i guess – Crab Bucket May 17 '14 at 21:36
  • @CrabBucket - logic ana mathematics are the "best candidates" to the status of a priori knowledge; still, there are some evidence against... According to some point of view, linguistic capacity is innate (and not conventional - see Chomsky); thus, we have a sort of "firmware" programmed to support us in the learning process of language. It seems that there are limits to the "possible" languages we can learn and use. If so, is there the "source" of our "logical" capabilities ? – Mauro ALLEGRANZA May 18 '14 at 7:39
  • Also linguistic capactity when seen gramatically, can be seen axiomatically. – Mozibur Ullah May 18 '14 at 15:44
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Common sense is merely non-formal, intuitive logic based on everyday experience of the real world.

The advantage of formal logic over common sense is that it can deal with proofs that are vastly more complex, and that it can deal with subject matters that are outside of everyday experiences, often yielding non- or even counterintuitive insights.

Conversely, the advantage of common sense is that it is intuitive and thus constantly and very quickly available without the need for lengthy, difficult proofs.

This makes common sense a good "sanity check" on formal logic: if your logical proof arrives at a result that contradicts common sense, then you most likely made a mistake and should double-check your proof.

Counterintuitive insights produced by formal logic are great (and often very valuable), but also not that common. They just get talked about a lot, because formally proving something that everyone already knew intuitively isn't exciting.

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So, in summary, Logic will be a means of proving/disproving common sense. Like, we have a path like this? ⬇️⬇️⬇️

1) Premise:Common sense➡️ 2) Sieve with: Tool of Logic ➡️ 3) Results:Facts.

Right?

And the results of arriving at an answer working with ONLY Common sense will be AN OPINION while arriving at an answer working with Logic will be A FACT.

  • It is unclear what the arrows are referring to. Could you add more explanation? References also would be helpful. They would strengthen your answer and give the reader a place to go for more information. Welcome to this SE! – Frank Hubeny Oct 28 '18 at 14:58
  • Hello, and welcome to Philosophy.SE. It has been brought to our attention that this answer seems to lack something. I will try to explain what I think this to be: First, it is unclear how this relates to the question. The question is about the use of common sense in logical analysis, i.e. in the use of logic. Secondly, your answer basically implies that you can somehow kind of transform common sense through the use of logic into facts. Thus, both how this relates to the question and how your proposed mechanism is supposed to produce facts needs further elaboration. – Philip Klöcking Oct 28 '18 at 15:21

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