LSAT Question Explanation
PT 109, Section 3, Question 23
Sufficient AssumptionArgument structure
Maria trained hard.
Maria won the race.
Explanation
The new information in the conclusion is pretty clear in this stimulus; we never talked about training hard in the evidence. We need an assumption that will prove that Maria trained hard based on the fact that she won. Put your prediction into this format: "If (insert evidence here), then (insert conclusion here)" as though you're creating a conditional relationship. After all, sufficient conditions guarantee necessary conditions, so if you make the evidence sufficient then your conclusion will definitely follow.
Here's my prediction: "If Maria won the race against Sue, the 4-time champ, then Maria trained hard."
Answer choices
This doesn't prove that Maria trained hard, just that she trained harder than Sue. They still could have both had mild or easy training regimens. This is a trap answer the LSAT will throw at you where they confuse an absolute concept (training hard) with a relative concept (training harder than Sue).
This is a very tempting trap answer because it seems to link the evidence and the conclusion. But does it prove the conclusion? Remember, our prediction for this answer was that Maria winning was sufficient for us to know that she trained hard. But this swaps the sufficient and necessary conditions compared to our prediction! Put more intuitively, this answer choice doesn't prove that she trained hard (the conclusion that we're trying to prove) based on the fact that she won (the evidence that we're working with). She could have not trained at all and still won if every other boat capsized, for example.
This works because it treats Maria winning as sufficient for us to know that she won. If she needed to train hard to win, then a win guarantees that she trained hard. This proves the conclusion and indicates why a proper prediction is so useful - use the format "if (evidence) then (conclusion) and don't get trapped by answer choice (B)!
This certainly doesn't prove that Maria trained hard, it doesn't tell us anything about her training.
This doesn't tell us if Maria trained hard. Maybe Sue just had a bad race.