I'm a bit confused. As far as I know realism is opposed to idealism.

But we can say that Plato was an idealist when speaking about Plato's forms. We also talk about Plato's realism in the philosophy of mathematics for instance.

I also read that Kurt Gödel was a realist who believed on the objective existence of mathematical objects (Source : https://plato.stanford.edu/entries/goedel/#GodRea). But aren't these ideas related to what we call idealism ?

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    don't get lulled into believing dichotomies are anything other than false constructs - useful tools for critical analysis, they are nonetheless illusory. Meaning is as much use as it is definition. See virmaior's comment about reading the terms in the context of their use. Note however that "metaphysics" is a portmanteau which was made up long after Aristotle's death while categorizing his extant errata which did not fit into his writings on natural science (physics). – Mr. Kennedy Dec 25 '16 at 5:20
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    Regarding "labels", Idealism is "a movement chiefly in the eighteenth and nineteenth centuries, although anticipated by certain aspects of seventeenth century philosophy.". – Mauro ALLEGRANZA Dec 25 '16 at 7:47
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    Idea from Descrates and Berkeley on, is a very very different concept with respect to Plato's εἶδος. – Mauro ALLEGRANZA Dec 25 '16 at 7:49
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    @Mr.Kennedy Yeah, you're right but it's still confusing sometimes, when I read wide-audience texts. – Boris E. Dec 25 '16 at 12:32

Both Plato and Gödel were mathematical platonists. Both held that mathematical objects existed abstractly and outside of spacetime. This is what we would call mathematical realism. This position is different from just the Forms because even Plato in The Republic and other dialogues distinguishes between the type of being exhibited by the Forms and by the mathematical objects respectively. Nevertheless the being that both Plato and Gödel take mathematical objects to have is what we call platonism, though emphasize more of how they exist just outside of spacetime than that they're 'ideal'; use the word 'abstract' instead.

  • Thanks for your answer. I will consider both yours and virmaior's answers as (complementary) answers to my question. – Boris E. Dec 25 '16 at 20:17
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    "Plato [was a] platonist"... Interesting. – Mauro ALLEGRANZA Dec 31 '16 at 16:09

The main thing happening here is a shift in the meaning of terms. Specifically, the word "realist" has had many many different uses over time. The basic idea is that a realist believes something is real, i.e. that such entities do in fact exist, that they are metaphysical objects in their own right (rather than existing as modalities on the mind).

Realism when used in reference to mathematical realism and Plato is that X is believes Y do in fact exist.

So Plato is a realist about Platonic Forms. Mathematical realists believe numbers do in fact exist.

Plato's view stands in contrast to Aristotle's view -- which while also realist with respect to forms does not think the forms exist as ideas. Instead, they exist as essences in substances. In contemporary language, this is the debate over universals. Anti-realist views think that these things only exist in our heads as words or concepts. (Realist views can of course accept that we also make words or terms for these things).

The term idealism doesn't generally occur in this debate. Idealism instead refers to views where things only exist due to the mind. It's a partial offshoot of rationalism generally associated with Schopenhauer. Hegel is often called an idealist as well, but I would argue this is a misnomer.

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    what exactly does the adjective "metaphysically" add to "real" here? It is superfluous if not downright oxymoron, no? – Mr. Kennedy Dec 25 '16 at 5:21
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    @Mr.Kennedy fair enough. reworded. The word metaphysics is worth mentioning here, but metaphysically real is either superfluous (for the real or the metaphysical) or unclear (as it doesn't make clear what the other possibilities might be). – virmaior Dec 25 '16 at 5:59
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    I would ask the same of "metaphysical objects in their own right" - does it not suffice to say "physical object"? (even that seems redundant but in the context of distinguishing the "mental" or abstract from the "physical" or "concrete"... words...) And "in their own right" - could they be in a wrong not theirs? I "get" what yer saying but such is language... – Mr. Kennedy Dec 25 '16 at 6:35
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    And what then is meant by "metaphysical"? – Mr. Kennedy Dec 25 '16 at 11:15
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    I'm not particularly familiar with quora, but the first answer in vertical order there is basically wrong. The answer by Abhishek Raj is basically correct. "Idealism" does not at least on its normal definition in philosophy mean that you believe Platonic forms (ideas) have the most reality; instead, it means that you think the only thing that exists are ideas (as in thoughts in people's heads). There is an idealist interpretation of Plato but it and idealism are much later than Plato himself. (see also the comment by Mauro on your question and plato.stanford.edu/entries/idealism). – virmaior Dec 25 '16 at 13:04

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