Necessary Conditions vs Sufficient Conditions (LSAT)

This distinction between necessary conditions vs sufficient conditions is among the most important concepts to understand when studying for the LSAT. I plan on writing about this topic throughout multiple posts, but I wanted to start with just a quick distinction. 

Imagine the statement: 

If a student hands in a permission slip, then the student can go on the school trip. 

Now imagine a student does not hand in the slip. Would we be justified in concluding that the student cannot go on the trip? We would not be justified in concluding that. Handing in a permission slip is sufficient for going on the trip. That's to say, we know enough to know that the student can go on the trip if the student hands in the slip. But handing in the slip is not necessary for going on the trip. And so not handing in the slip tells us absolutely nothing about whether the student can go on the trip. 

Let's change it up a bit. 

A student can go on the school trip only if the student hands in a permission slip. 

Now imagine a student hands in the slip. Do we know that the student can go on the trip? We do not. Handing in the permission slip is required for going on the trip. We know that if the student does not hand in the permission slip, the student cannot go on the trip. But because the condition of handing in the slip is required rather than sufficient, by handing in the slip we know nothing. If the slip is handed in, maybe the student can go on the trip, maybe the student cannot. We do not know. 

Summary:

In short, if a sufficient condition is satisfied, we can draw a valid conclusion. If a sufficient condition is not satisfied, there is no valid conclusion to draw. If a necessary condition is not satisfied, we can draw a valid conclusion. If a necessary condition is satisfied, there is no valid conclusion to draw.