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My car is blue, but it could be red;
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it could exist as a red car.
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And even if I never,
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over the entire course of existence of my car,
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never get it painted,
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so that from the moment it came into creation to the moment
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it gets smashed it's always blue--
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still, we understand perfectly well the idea
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that it could've been red.
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There's nothing incompatible with the idea
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that this car exists and is red.
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So that's an example of a contingent property.