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I am not a philosopher but I would like to ask this question. I know that there are philosophers like Hobbes, Locke or Foucault, who excel in the areas of ethics, political philosophy and aesthetics. However they rather use informal logic than formal/symbolic logic in dealing with practical problems posed by the respective field because informal logic is rather concerned with substance than with structure. I suppose that other, not this well known philosophers, are good in symbolic aspects, too. So can one be a philosopher without much knowledge of formal logic?

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You don't need formal logic; you only need to reason well. Formal logic is a way of reducing good reasoning to techniques which might be described as calculation, in which it is easier to catch yourself (or others) in invalid modes of reasoning. As to mathematics: it is best used as a tool for grasping how you might model complicated situations --- even if you can't actually measure the qualities you are considering, it helps to hone your intuitions for how to reason about complicated situations. So they aren't necessary, but they help. – Niel de Beaudrap Nov 10 '12 at 18:40
See also… – DBK Nov 11 '12 at 13:57
Isn't that even a duplicate? – iphigenie Nov 11 '12 at 15:00
@iphigenie - Math vs logic; it's close depending on how you view either. You're free to vote to close if you think it's a duplicate; I'm willing to see if this pans out to something tangential first. – stoicfury Nov 11 '12 at 19:08
An excellent question! It shows so well pathetic failures of this site - lots of participants simply do not know what a consistent argument is! – მამუკა ჯიბლაძე Mar 27 '15 at 9:31

You must at least understand logic, especially symbolic logic because it underpins many areas of philosophy, not to mention mathematics. For example, Kant would not have written such great books if he was not interested in logic. He even studied mathematics in his spare time. He also played around with many natural sciences like physics. I doubt he ever published anything, but I know he actually explained why galaxies and solar systems lie in planes using conservation of angular momentum. Some people like Russell and Godel start by studying philosophy but then realize that they are much more interested in logic, paradoxes, proofs, etc. You must also understand that there is not just propositional logic, there are things like modal logic for example. Overall, many great mathematicians were also philosophers, and vice versa. For instance, Leibniz and Descartes are among many.

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It is almost impossible to have a career in philosophy in the modern anglophone world without being a very sound logician. It is not, however, strictly necessary for the pursuit of strong academic philosopher. A lack of a strong grounding in logic will exclude you from much of the contemporary conversation, plus a strong formal education will sharpen your analytical capacity.

I know well-studied and competent phenomenologists who have never studied formal logic and are not interested in logic or mathematics in the least and have never shown any competency in them. It is definitely possible, although inadvisable and a poor professional decision.

Then again, I'm not sure there's any domain of knowledge that will not make for a more sophisticated and capable philosopher.

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This doesn't seem right at all. There are certainly plenty of ethicists, political philosophers and so on who no next to no formal logic, and get by fine. There are also plenty of metaphysicians, epistemologists and so on who get by fine with only a little bit of logic knowledge (enough to follows some short argument maybe). That said, education in formal logic is certainly no bad thing, and very helpful. – J.P. May 9 '14 at 16:38
"It is almost impossible to have a career in philosophy in the modern anglophone world without being a very sound logician... I know well-studied and competent phenomenologists who have never studied formal logic and are not interested in logic or mathematics in the least and have never shown any competency in them. It is definitely possible, although inadvisable and a poor professional decision." Apparently phenomenologists do incredible things everyday!!! Would those phenomenologists really describe what they do as "almost impossible"? – Doug Spoonwood May 12 '14 at 15:25
@J.P. - A significant portion of the contemporary ethical papers that I read contain sections written in Predicate Logic. Obviously they don't have to be logicians or concern themselves with the differences between implication and entailment, but that's the difference between using a system and studying it unto itself. – wmjbyatt Aug 19 '14 at 21:59
@DougSpoonwood - The well-studied and competent phenomelogists that I know all struggle to get work, and when they do it's in literature departments. So yes, I would describe being employable with their education as "almost impossible," which is what my original comment said. – wmjbyatt Aug 19 '14 at 21:59

I don't think it all necessary. It's reasoning, judgement & imagination thats important. Of course it does depend on what area of philosophy you are interested in.

There have been philosophers who have been good mathematicians & philosophers. Descarte & Pascal comes to mind. But its reason that grounds both. You appear to slight the authors you mention because they're using 'informal logic'. Would could it mean to formalise their logic? Would it make it more comprehensible?

Although Plato idolised geometry, I doubt you'll find it (in a formal sense) in any of his works.

Hegel wrote 'The Science of Logic', and even that doesn't treat formal symbolic logic. Since for Hegel "the underlying structure of all of reality is ultimately rational, logic is not merely about reasoning or argument but rather is also the rational, structural core of all of reality and every dimension of it. Thus Hegel's Science of Logic includes among other things analyses of being, nothingness, becoming, existence, reality, essence, reflection, concept, and method".

But, if you're interested in Badious work, you'll need a heavy dose of Set Theory.

To understand Nietsche you need a literary imagination, since his strategies are either poetical or rhetorical, even if his concerns are not.

Spinoza wrote in a proposition - theorem style as homage to Euclid. But I don't think his concerns are formal either. Wittgenstein wrote in a similar style. But he was also interested in formal logic (an inheritence from Bertrand Russell perhaps), but he denounced mathematics as merely syntax & tautology, which as a lapsed mathematician, hurts.

If you're interested in metaphysics & mysticism, you might find that the philosophy encoded in metaphysical/mystical poetry more accessible.

Lastly if you don't like formal symbolic logic, avoid it :), but if you do go for it!

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I would downvote this if I had enough reputation points. A philosopher at least needs to distinguish between correct and fallacious arguments. If there is no agreement about that then I believe it is impossible for philosophers to communicate anything between each other. And after all formal logic is just such an agreement and nothing else. – მამუკა ჯიბლაძე Mar 27 '15 at 9:28

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