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Conditional Statements Made Easy: Unlock Sufficiency and Necessity with These Four Words


If you’ve just started studying for the September LSAT, you’re probably learning about conditional statements right now. In two posts this week, we’re going to simplify the process of learning how to diagram these occasionally daunting statements. Today we’re going over how recognize sufficient and necessary conditions.

There are lots of words you can use to express a conditional statement. If you’ve started studying for the LSAT, you’ve probably seen a list of sufficient and necessary condition indicators. It’s well worth memorizing those, but don’t let the memorizing stop you from thinking. No list will be exhaustive, and you want to be confident you can diagram a conditional statement even if it’s introduced with words that aren’t on the list or if you don’t trust your memory.

There’s a simple way to figure it out. Before we get there, a quick refresher: the sufficient condition is the one on the left side of the arrow, while the necessary condition is on the right. For example, let’s say that you’ll be embarrassed if you accidentally hit “reply all” to an email. “If” introduces a sufficient condition, so the diagram is:

Accidentally hit reply all → Embarrassed

Hitting “reply all” is sufficient in this case, or enough, to lead to embarrassment. Embarrassment is the necessary consequence. Now onto the quick trick.

Remember these two sufficient condition indicators: “if” and “all.” There are many more, but many of them are effectively synonyms of these two words. “Every” is a lot like “all,” so that’s also a sufficient indicator. “In the event that” is pretty much the same as “if,” so that’s another sufficient indicator. You can even stretch it a little further. Let’s go back to third grade and say that whoever smelt it dealt it. “Whoever” isn’t exactly a synonym of “if” or “all” but it wouldn’t change the meaning of the sentence to say “If you smelt it, you dealt it.” So the diagram is:

Smelt it → Dealt it

The same works for necessary conditions. Remember these necessary condition indicators: “only” and “necessary.” These words and their synonyms introduce necessary conditions. So, if you see “requires,” well, “required” is a synonym of “necessary” so that’s a necessary condition. What if something is called a “precondition?: That means necessary, so it’s a necessary condition.

Don’t let this trick keep you from memorizing those lists. It’s worth it, and some indicator words are a bit trickier—stay tuned for another blog post about diagramming this week. But it’s easier to remember the lists if you understand the concepts of sufficiency and necessity. And by using those basic concepts, you can diagram a conditional statement even if it doesn’t use any of the indicator words on your lists.