Laura is the sister of either Rachel or Sandy, and Sandy is the sister of Beth. Therefore, it follows necessarily that Laura is the sister of Beth.
A) Deductive, invalid.
B) Deductive, sound.
C) Inductive, strong.
D) Deductive, valid.
E) Inductive, weak.

Question

Quizplus · Accepted Answer

The argument is deductive because it attempts to draw a necessary conclusion from the premises. However, it is invalid because the conclusion (Laura is the sister of Beth) does not necessarily follow from the premises given the possibility that Laura is the sister of Rachel, not Sandy.

Laura Is the Sister of Either Rachel or Sandy, and Sandy