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Edited by Richard Walker, Friday, 27 Aug 2021, 15:57
All roses are flowers.
Some flowers fade quickly.
Therefore some roses fade quickly.

Is this a valid inference?

Source: Thinking fast and slow, by Daniel Kahneman

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Hi Richard,

I don't think that this is a valid inference because it doesn't identify roses as being among those flowers which fade quickly. No particular flowers which fade quickly are identified.


Richard Walker

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Yes I agree! Most people are inclined to accept the inference and it does seem intuitive, but as you say, roses and fast-fading flowers may have no overlap.