2020 LRB p. 223

[Zarie Blackburn]

We recently received the following question from a student. An instructor will respond below. Thanks!

I'm having a hard time distinguishing between necessary and sufficient conditions. I don'y entirely understand how a necessary condition can be defined as "an event or circumstance whose occurence is required in order for a sufficient condition to occur." For example, in the sentence "If you are rich and famous, then you are happy," being happy is the necessary condition, but it isn't required for the sufficient condition (people being rich and famous). If it were, wouldn't that be a Mistaken Reversal? I have been trying to diagram these conditions by rephrasing problems into "in order for X, then Y," but that doesn't always work because their relationship isn't always causal. I would appreciate any advice on better identifying the conditions.

[Adam Tyson]

It sounds to me like you may be confusing conditional reasoning with one or both of two things: 1) causal reasoning and 2) the real world.

In the real world, happiness is not required for being rich and famous. I'm sure there are plenty of rich, famous people who are sad and lonely! But if you are faced with a claim like that one on the LSAT, then you must ignore what you know about the real world and accept it as absolute fact - rich, famous people MUST be happy, no room for doubt about it.

Conditional reasoning is also not causal reasoning (although it often looks like there is probably a causal relationship going on, and conditional premises can and often do lead to causal conclusions.) The statement, as given, is not saying that being rich and famous MAKES people happy, and it is also not saying that being happy makes you rich and famous, or that you cannot be happy unless you are rich and famous (that last one is the true Mistaken Reversal.) It is just saying IF you are rich and famous, THEN you must be happy. In this twisted alternate reality, happiness is, for those rich and famous folks, 100% guaranteed.

So when we say that happiness is required for the sufficient condition, that's exactly what we mean, and what that sentence says. Happiness is the necessary condition, so it is required every time the sufficient condition occurs. Being happy proves nothing - it is not sufficient - but when the sufficient condition occurs, the necessary condition of happiness must also occur.

Conditional reasoning isn't something we use much in daily life. We aren't usually so rigid in our thinking, and we know that life is full of exceptions to broad claims like these. The tough part on the LSAT is ignoring that sort of real-world thinking, getting rid of exceptions, and accepting conditional claims that may seem bizarre or ridiculous in light of what we know and believe. Mechanically applying the rules of conditional reasoning, with the indicator words helping us to sort out what is sufficient and what is necessary and then building diagrams to help us keep it all in line, is like learning to ride a bike. It may not be natural or comfortable at first, and you will surely fall a few times before you get the hang of it, but once you get it you will never be able to forget it, and it will all start to come to you with much greater ease. Keep at it, and you'll get there!

[Dave Killoran]

Just to add to what Adam posted: We talk about conditional reasoning here and on our blog very frequently, and so there are a ton of places you can go to learn more about the concept. It's also a topic you'll see in both LR and LG a lot, so it's good that you are asking questions now about it! Here's some articles/threads to review when you have time:

• Avoid Real World Interpretations and Follow the Language: http://forum.powerscore.com/lsat/viewto ... p=216#p216
  
  One More Look on what Sufficient and Necessary Means (this is key so that when indicators aren't present, we know what we're doing): http://forum.powerscore.com/lsat/viewto ... 6166#p6166
  
  LSAT Conditional Reasoning: When To Diagram: http://blog.powerscore.com/lsat/bid/333 ... To-Diagram
  
  The PowerScore LSAT Blog, Conditional Reasoning articles - https://blog.powerscore.com/lsat/catego ... reasoning/. We write often about this concept, and there are over 20 articles here discussions all sorts of interesting conditional language and arrow relationships.
  
  My posts on this Forum, all searchable: https://forum.powerscore.com/lsat/searc ... 3&sr=posts