Sufficiency and necessity are the most consistently tested concepts on the LSAT. Mastering these two skills will vastly improve and stabilize your LSAT score. In the Kaplan LSAT class, we introduce the concepts of sufficiency and necessity during the first class session. Not only must LSAT students understand these concepts, but the ability to manipulate these abstract terms is the hallmark of a student poised to achieve a top LSAT score. When an LSAT student begins to grasp the essence of how sufficiency and necessity relate and affect each other, LSAT scores begin to make dramatic leaps. So, let me explain what sufficiency and necessity are and why they are such important LSAT skills.
Imagine you have bought a box of brownie mix. You are excited to start mixing ingredients and begin cooking. Is the bag of brownie mix sufficient to make your brownies? When I say sufficient, you should automatically substitute the word “enough” for sufficient. Is the bag of brownie mix “enough” to make the brownies? Is that all you need? Unfortunately, no. The box of mix is not sufficient, not “enough”. You read the back of the brownie mix box, and it says you need to add an egg, water and oil to the bag of mix. Is an egg, alone, sufficient (enough) to make the brownies? No. Is water, alone, sufficient (enough) to make the brownies? No. Although it would be awesome to be able to make brownies from only water! None of the individual ingredients is “enough” to make the brownies. But each individual ingredient (mix, egg, water, oil) is necessary to successfully make the brownies. When I say “necessary”, you should think “needed”. Eggs are needed. So that means eggs are necessary. Water is needed. So water is necessary. Each ingredient is individually needed (necessary), but no ingredient alone is enough (sufficient). Each ingredient is necessary, but not sufficient.
Here is another way to visualize necessity and sufficiency: imagine an island that is accessible by only one bridge. That one bridge is necessary (needed) to get to the island. If the bridge is necessary, but unusable for some reason, then you would not be able to reach the island. If a necessary (needed) element is not available, then the result of reaching the island cannot happen. The one bridge is both necessary and sufficient. However, if there are three bridges that give you access to the island, then none of the individual bridges is necessary (needed), because you have three options. In this three bridge scenario, Bridge #1 is not necessary. Bridge #2 is not necessary. And Bridge #3 is not necessary. But, any one of the bridges would be sufficient (enough) to allow you to reach the island. In this three bridge example, each bridge is sufficient (enough) to reach the island, but no one, specific bridge is necessary (needed). Each bridge is sufficient, but not necessary.
Here is one more clarifying example of the necessity and sufficiency concepts: You need to be 18, or over, to vote. It is necessary to be at least 18 to vote. You provide evidence that you are 18. Does that mean you can vote? No. Being 18 is only one necessary criteria. In order to vote, you also have to be a citizen of the United States, not a felon, and registered to vote. Each of those criteria are necessary (needed) before you will be allowed to vote. Being over 18 is necessary (needed) to vote, but not sufficient (enough). If you tell me you voted, that is sufficient (enough) evidence to allow me to deduce that you met all the necessary criteria. When facing an LSAT question about sufficiency and necessity, try to simplify each element, and ask if the element is needed. If you must have that element, the element is necessary. If the element is one of a multitude of ways of reaching the goal, then that element is sufficient (enough), but not necessary. “Sufficient but not necessary” means there are other ways to achieve the result.
Next week, I’ll share how these important skills translate in the law.