- Tue Apr 25, 2023 12:47 pm
#101381
Hi Todd,
Careful with diagramming your conditional rules and contrapositives! You've made a Mistaken Reversal, which is a fundamental error that the LSAT loves to test.
First, this is an advanced linear game. The basic setup would be a horizontal diagram with the crops on the bottom row and the fertilized/irrigated variable set on the top row. (I mention this because the visual diagram of the rules reflects how we set up the main diagram.)
Rule 4 basically states that if V is earlier than R, then oats are fertilized.
This is a conditional sequencing rule and could be diagrammed:
(V - R) -> oats fertilized (which I'd diagram as an OF vertical block with F above O). I like to put my sequencing rule in parentheses to clearly separate it as the sufficient condition.
The contrapositive of this rule, which should also be diagrammed, would normally be:
oats not fertilized (which would be diagrammed as an OF vertical block with a slash through it) -> V is not before R (which would be (V - R) with a slash through it.
However, because there are only two options for the crops (fertilized or irrigated), not being fertilized means being irrigated. Also, since all of the variables are used and there are no ties, V not being before R means that R must be before V.
So a more helpful way to diagram the contrapositive is:
oats irrigated (which would be diagrammed as an OI vertical block) - > (R - V)
Notice how (R - V) is the necessary condition in the above diagram of the contrapositive. Because it is the necessary condition, it does NOT mean that the oats must be irrigated. You can have the necessary occur without the sufficient occurring. That is a classic Mistaken Reversal. (Notice that the arrow only goes one way, from the sufficient to the necessary, not the other way around.)
If you are not familiar with the details of conditional reasoning or need additional help with the topic, it is covered in lesson 2 of our LSAT course and in chapter 6 of The Logical Reasoning Bible.
