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All-some-some Invalid Argument (NAME?)

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Original Question
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.

Answers

5
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.
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.
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

Basic rule: no valid syllogism can include the word "some."
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