Anatomical bilateral symmetry is a common trait. It follows, therefore, that it confers survival advantages on organ...

timothy October 3, 2017

QUESTION 30

How do you workout which is just the Principle and which is the premise. I notice that in answer choice E you said it had 2 principle are there word indicators to know that the following is a principle or just a premise? Thanks.

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Mehran October 3, 2017

Hi @timothy, thanks for your post. A principle can be defined as a statement that has both a sufficient and a necessary condition.

As explained in the video, this stimulus contains an argument. The conclusion is that anatomical bilateral symmetry confers survival advantages on organisms. Why? Because it is a common trait (according to the stimulus).

PR: not CSA ==> not CT
CP: CP ==> CSA
[general principle]

P: CT [invokes contrapositive of general principle]

C: CSA

This is a valid argument — the premise invokes the contrapositive of the general principle.

OK. Let's compare that to the pattern of reasoning found in answer choice (E):
PR: WAA ==> DRP
CP: not DRP ==> not WAA

PR: not WAA ==> Absurd
CP: not Absurd ==> WAA

Here you have two general principles (two statements with a sufficient and a necessary component each). That's structurally different from the pattern of reasoning in the stimulus (which contains only one principle), and so answer choice (E) can be eliminated.