Question

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All-some-some Invalid Argument (NAME?)

I'm looking for a specific name (i.e. affirming the consequent). Some have suggested fallacies with "if-then" format, which doesn't apply to this, which is an "all-some" format.

All X are Y.
Some Y are Z.
Therefore, some X are Z.

Example:

All roses are flowers.
Some flowers fade quickly.
Therefore, some roses fade quickly.

The conclusion doesn't follow from the premises (it's invalid) even though each premise and the conclusion happens to be true.
asked on Monday, Jul 01, 2019 10:02:39 PM by

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Answers

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Jim
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I can't say exactly what fallacy this is, but a Venn diagram of the argument has a large circle called Flowers, a smaller totally-contained circle called Roses, and another small totally-contained circle called Fade Quickly. The two smaller circles may or may not overlap.
answered on Tuesday, Jul 02, 2019 08:58:22 AM by Jim

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Bill
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Basic rule: no valid syllogism can include the word "some."
answered on Tuesday, Jul 02, 2019 10:32:05 AM by Bill

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Bill
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So I asked around on Reddit, and it seems that this fallacy doesn't have a name for it's "all-some-some format". So I decided to name it; the "Ambiguous Property Fallacy"; it's ambiguous because we don't know if the property (fading quickly) applies to roses or not, even though it applies to flowers.
answered on Tuesday, Jul 02, 2019 12:56:01 PM by Bill

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Bryan
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Have a look here<>

in the section syllogistic fallacies, I think that would fall under:

Undistributed middle: Neither of the premises accounts for all members of the middle term, which consequently fails to link the major and minor term

I'm far from an expert on syllogisms but according to the basic structure section "some" can be used.

answered on Tuesday, Jul 02, 2019 05:02:16 PM by Bryan

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DrBill
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I think it's an example of the formal fallacy of the undistributed middle en.wikipedia.org/wiki/Fal. . .

One way to spot the fallacy is to reframe the syllogism to force the middle to be distributable

All roses are flowers.
Some flowers fade quickly.
All roses share the property of fading with all flowers
Therefore, some roses fade quickly.

The offset premise actually anticipates the consequent, but

All roses are flowers.
Some roses fade quickly.
Therefore, some flowers fade quickly. is actually valid and sound

answered on Tuesday, Jul 02, 2019 06:55:45 PM by DrBill

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