#14 - Local, Could Be True

[Administrator]

Complete Question Explanation
(The complete setup for this game can be found here: lsat/viewtopic.php?t=11115)

The correct answer choice is (C)

From the discussion of inferences, when L is offered, then G, H, and Z must be offered, P and S cannot be offered, and M may or may not be offered. As this is a Could Be True question, immediately attack the uncertainty in this question: M. Only answer choice (C) addresses M, and as it could be true that M is not offered, answer choice (C) is correct.

[diwil]

Hello,

Thank you in advance for your help.

I got to the correct answer, (M not being offered/IN), but I am not quite convinced.
If L is Offered/IN, then G is also offered/in and P is Not offered/out. IF P is out then S is out. (I need S AND L to be out/not offered, in order to have M also not offered/out, right? That's the contrapositive of M -> L or S (first rule).
If L AND S MUST BE OUT (for M to be out), THEN I am not sure why M is out (because L is IN). I do have S out, but not L (L is In/being offered).
By process of elimination I ended up with M not being offered (letter C), but that would require my contrapositive to be:
IF L out OR S out, then M out. Right? However, my contrapositive is IF L out AND S out, then M out.

I am not sure if I made myself clear. Let me know if you understand my question, and thank you in advance!

Thank you for your help.

[Adam Tyson]

Hey there diwil, I understand where you are coming from, and it looks like you are making a Mistaken Reversal of conditional logic.

When M is in, you need exactly one of L or S. Either L is in and S is out, or S is in and L is out. That means there are two ways to prove that M is out, using the contrapositive - if L and S are both OUT, or if L and S are both IN. Either of those would force M to be out. But, as it turns out, L and S can never both be in, as you correctly surmised due to what they each do to P.

So, M requires exactly one of L or S to be in. But having one of them in does not require that M be in - that is the mistaken reversal. M could be in, OR M could be out - it's optional at that point! The necessary condition (one of L or S) has been met, so the sufficient condition (M is in) MAY be met, but doesn't NEED to be met.

One last thing - this question isn't about what MUST be true, but about what COULD be true. It could be true that M is offered, and it could be true that M is not offered, because it is optional when L is offered. The other four answers cannot be true - S must be out, H and Z must be in, and there are at least 4 courses being offered (LGHZ).

Remember, when a necessary condition is met, the sufficient condition is just an option. Don't go backwards, stabbing yourself on the point of a conditional arrow, and conclude that the sufficient condition must occur! It's sufficient, but it isn't necessary!