Rule Substitution Questions (LSAT)

Rule substitution questions are among the trickiest and most time consuming questions on the Logic Games section of the LSAT. Some of them are just brutal. 

But, like so much on this test, there's a technique or a strategy when encountering them. Here is what a rule substitution question looks like: 

"Which of the following if substituted for [some rule that was presented in the game] would have the same effect in determining [something important about the particular game]."

When you come to a question like this, you've got to understand what it's asking. The question requires that you remove from the game some rule that was provided, and substitute that now-removed rule with a new rule only applicable to the particular question. And the new rule that effectively substitutes the old rule will be the correct answer to the question.

But, and this is the key, when substituting that rule (thereby choosing the answer), neither of the following two things can happen:

The rule can not make the game any more limited that it already was

and

The rule can not make the game any less limited than it already was. 

For example, let's say there's a sequencing game with five slots and we're told that R cannot go into slots 1 or 2. In other words, R can only go into slots 3, 4, or 5. 

_ _ R _ _ 

_ _ _ R _ 

_ _ _ _ R

If an answer choice in a rule substitution question provides for a new rule that would allow R to go into slots 1 or 2, it's incorrect since that would make the game less limited that it was prior to the substitution. And if an answer choice provides for a new rule that would not allow R to go into slots 3, 4, or 5, it's incorrect since that would make the game more limited than it was prior to the substitution. 

Let's say there was another rule in this game that said T must go into slot 2.

_ T R _ _ 

_ T _ R _ 

_ T _ _ R

Assume we're told in a rule substitution question that the rule eliminated is the rule that R must go into slots 3, 4, and 5. And one of the answer choices for substituting that rule is that R cannot go before T. That would be excellent here because by saying that R cannot go before T, it's effectively saying that R must go in 3, 4, or 5. It's not making the game any more or any less restrictive than it was when the rule was that R must go into slots 3, 4, or 5. Substituting that rule with the old rule does not change the game at all.

Granted, that's a very simple example, but start with the simple. Understand the logic first and then move on to applying that logic to more complicated scenarios.