October 2010 LSAT Section 1 Question 19

Passage B differs from passage A in that passage B is more

the66guy on November 1, 2021

Question 6

How do you know that the child having type O blood is sufficient and the father having type B blood is necessary? I’m very confused. Can an instructor please explain? Thanks I’m advance

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Jay-Etter on January 23, 2022

So the argument is
Parent: If parent type O -> children type O
Student: this is false, because father has B and I have O.

The student is assuming that the child having type O blood is sufficient to know that the father has type O blood, but that this conditional is wrong because their father has type B blood, and this is why the student disagrees.

Note that in reality, the child having type O blood is actually the necessary condition (based on the conditional given to us by the parent). However, the student is treating the child having type O blood as the sufficient. If the student interpreted the conditional correctly, then there would be nothing wrong with them having O and their father having B, and they wouldn't have an argument at all. I hope this helps, feel free to follow up with further questions.