All squares have four sides. Some rectangles have four sides. Therefore, some squares are rectangles. This syllogism is:
A) Valid
B) Invalid (undistributed middle term, four sides)
C) Valid, but unsound
D) Probably valid
E) Probably invalid

Question

Quizplus · Accepted Answer

The syllogism is invalid because it commits the fallacy of the undistributed middle term. The fact that both squares and some rectangles have four sides does not logically lead to the conclusion that some squares are rectangles.

All Squares Have Four Sides