We have definitions for both a square and a circle. By definition, I understand that it's impossible to have a square circle. However, why does the word 'square' have to necessarily mean 'a plane figure with four equal sides'? Conceivably, the word square could have been defined as a 'round plane'? Thus making 'a square circle is metaphysically impossible' false?

I'm new to philosophy. So if this question is pathetic I apologize.

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    Welcome to Philosophy SE! It's a good question! Quine notwithstanding, the meaning of the words, or what they describe is what matters and what can be said to be possible or impossible, not the words themselves. Once the meaning is fixed, some things may become impossible. For example, married bachelors are impossible because "bachelor" means unmarried man. You could define bachelor to mean something other than the "standard" definition, but you wouldn't be showing that married bachelors are possible, you'd just be showing that married <whatever-you-define-bachelor-to-mean>s are possible. – Adam Sharpe Apr 5 '19 at 21:00
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    I wish philosophers would choose a different example. The unit circle is a square in the taxicab metric. en.wikipedia.org/wiki/Taxicab_geometry. What the saying means is that a definition is a definition. You can't have a married bachelor because a bachelor is unmarried by definition. But you can have a square circle! – user4894 Apr 5 '19 at 21:15
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    The word "square" is a string of letters, it can mean whatever people agree it to mean. So it is vacuous to ask what is "metaphysically possible" for a string of letters to mean. Anything. Therefore, when people talk about metaphysical possibility they do not refer to strings of letters, but to the senses currently attached to them, see SEP on Metaphysical Possibility. – Conifold Apr 5 '19 at 21:18
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    @user4894 Very neat. But I'd argue that "everyday" geometry is implicitly Euclidean, and so we should give the "square circle" example a charitable interpretation. I think it's like someone saying 1+1=10 is impossible, and you objecting that it's a bad example because 1+1=10, in base 2. The everyday reading of numbers is base 10, and that is how they meant to be implicitly understood. – Adam Sharpe Apr 5 '19 at 22:01
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    Although it is pretty nearly universally accepted that a square circle is metaphysically impossible, there doesn't seem to be any agreement that I can find as to why. I suspect a lot of people will point out that we can deduce a logical contradiction from the definitions/axioms in Euclidean geometry, but then we're introducing additional terms/symbolism so that the "square circle" itself doesn't strictly entail a logical contradiction. For my own part, I'd simply say I have no way to make sense of a square circle, and I intuit from this its metaphysical impossibility. But that's me : ) – Ben W Apr 5 '19 at 23:18

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