Q9 - If a mother's first child

[danlage81]

I understand why the right answer is right, in so much as it "parallels" the stimulus. My question is, why is the argument flawed?

I diagrammed it as "If A, then likely B, so if not B, then likely not A"


I just don't see why this is a flawed relationship.

[hwsitgoing]

I had the exact same question!

Ideas anyone?

[danlage81]

Come on guys, there are some smart people here. Anyone please.

[ManhattanPrepLSAT1]

The reason is that likelihoods are not conditionals. And even though we see the "if/then" in the evidence, within the "then" part we see the word "likely" which transitions this to a statement about frequency. We use three (3) kinds of statements.

All statements - All A's are B's
A ---> B

Most statements - Most A's are B's
A most B

Some statements - Some A's are B's
A some B

All = 100%
Most = 50+% (up to and including all)
Some = 1+% (up to and including all)

For "most" statements we cannot reverse or negate the logic just like we can't do this for conditional relationships. Also, there are no contrapositives for "most" statements.

The word "likely" is translated to a most statement and this argument would sound in generic form like

A most B
-----------
~B most ~A

That's an attempted contrapositive, but there are no contrapostives of "some" and "most" statements. Answer choice (C) has the same attempted contrapositive of a "most" statement.

(A) has negated a "most," but doesn't reverse the direction of the statements. The stimulus both reversed and negated the "most" statement.
(B) has reversed a "most" statement. This answer choice forgot to negate the "most" statement.
(D) puts the likely in the wrong part of the conditional and turns the evidence into an "all" statement.
(E) never includes a likelihood and represents simply pure "all" statements. More formally we call them conditional statements.

Sorry for the delay, but does that explanation help address some of your questions here?

[erho]

Great explanation.
I think I saw this as...
A causes B DOES NOT mean B causes A.

[nbaronia]

Should we usually think of and diagram the word "likely" as a "most" statement whenever it pops up in a question like this?