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I just started studying the Manhattan Logical Reasoning prep book and I am somewhat confused with how to evaluate the logic of "necessary" assumptions and "sufficient" assumptions. I cannot instinctively grasp the cores of arguments along with their assumptions. I can if I write them out, but that would be impossible during the real exam. Then come the questions asking you to determine the "necessary" and "sufficient" assumptions. I am a visual learner. I need to see diagrams and my thoughts need to be written down to analyze things. How do all of you LSAT experts determine these assumptions in your mind without writing them down? Did you have these same issues when you first began studying for the LSAT? Will determining assumptions come easier to me the more I study?

To determine if the assumption question is necessary or sufficient, you look at the "Question Stem". If it says "required", "necessary", or something similar, then it's a necessary assumption question. You attack those by figuring out which answer choice the argument relies on (Negation Test).

Sufficient assumption questions will be something like "which one of the following allows the assumption to be logically correct". For these, you just need to pick an answer that fills the gap in the argument's logic.

I hope that helps a bit anyways.

tomjennings wrote:I just started studying the Manhattan Logical Reasoning prep book and I am somewhat confused with how to evaluate the logic of "necessary" assumptions and "sufficient" assumptions. I cannot instinctively grasp the cores of arguments along with their assumptions. I can if I write them out, but that would be impossible during the real exam. Then come the questions asking you to determine the "necessary" and "sufficient" assumptions. I am a visual learner. I need to see diagrams and my thoughts need to be written down to analyze things. How do all of you LSAT experts determine these assumptions in your mind without writing them down? Did you have these same issues when you first began studying for the LSAT? Will determining assumptions come easier to me the more I study?

Hey There, let me see if I can give you a bit of air support. Mostly my point is to tell you not to worry - as the above poster mentions, you can generally tell from the question stem whether you're looking for a sufficient or necessary assumption. Here are the big ideas you should have in your pocket:

1. Sufficient assumptions are broader than necessary, as they make the argument "work." They're often more predictable.

2. Necessary assumptions can seem "annoying" in that they are not always something you can predict. But, you can test out if an assumption is necessary by negating it. If the negated form destroys the argument, then it's necessary!

All of this is in the book, but I get the sense you're getting a bit nervous because you're thinking you can predict the assumptions, or that you're regularly asked to decide if an assumption is necessary or sufficient. Once in a while, the LSAT asks for a necessary and throws you a sufficient one that's not necessary - that's the only real twist you need to watch out for. And for that, you've got your handy negation test. Your job is not to determine the assumptions before looking at the answer choice, your job is to get to the core of the argument so that you'll be able to evaluate the answer choices (though, with sufficient assumption questions, a bit of prephrasing won't hurt).

I hope that helps.