Necessary condition definition

[rach45]

I am having a hard time understanding conditional reasoning conceptually. I can do the diagramming and stuff, but to put the definitions of suff and nec conditions into my own words is another story. The definition of a necessary condition in the book threw me, it says, "A necessary condition can be defined as an event or circumstance whose occurrence is required in order for a sufficient condition to occur."

I am not understanding the "in order for" part. I thought it was the complete opposite, that the sufficient condition was required in order for/enough for the necessary to occur. In my head, this definition is like a mistaken reversal, where you incorrectly say that if the necessary has occurred, the sufficient also occurs.

Thanks in advance!

[Rachael Wilkenfeld]

Hi Rach,

Conditional reasoning can be hard to wrap your head around, but I promise you've used it before without even realizing it. You just have to formalize things that you've done before.

The definition you posted from the book is correct. The key is that the necessary condition is the required condition. It's needed, absolutely positively, in order for the sufficient to occur. Sometimes it can feel awkward to phrase it that way, because we think of the sufficient condition first, but there's not a time element there. It's just saying that the necessary condition is required for the sufficient.

Let's think about some conditional reasoning you might remember from your childhood.

If you want to go to the movies, you need to do your homework.

What's necessary? Homework. What's sufficient? Going to the movies.

You knew if you wanted to go to the movies, you had to do your homework.

Try and think about conditional reasoning in a single simple example. It can be any example that makes sense to you, but I like to use a simple if---->then statement like the movie/homework example. I also think it's often easier to think about what the statement thinks is necessary first. Even though the necessary condition will always go at the end of the arrow, it's often the easier term to identify.

Hope that helps!
Rachael

[Dave Killoran]

Hi Rach45,

Adding to what Rachael said, there are tons of comments and posts on our site that help explain conditional reasoning in more detail, so you are in luck! Here's a good starter list of things to read that might help here:

• 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: lsat/search.php?author_id=63&sr=posts
  
  And keep an eye out for the Free Seminars we occasionally do on this topic! https://www.powerscore.com/freeseminars/

Thanks!

[BMZ789]

Hello guys,

Honestly I still didn't get the answer.

I understand the diagraming, and the fact that if a necessary condition happens, then the sufficient condition may or may not have happened, so why is the necessary condition's definition in the way that rach mentioned.

"Necessary condition is an event whose occurrence is "Required IN ORDER" for a sufficient condition to occur" It feels to me that its literally the same definition of a sufficient condition. why can't the definition be

" Necessary condition is an event whose occurrence is required when a sufficient condition occurs"

[Beth Hayden]

Hi BMZ,

That wording definitely works as well! You just want to make sure that you don't interpret the word "when" to imply that the sufficient condition always happens first. There is no timing element to conditional reasoning per se--the necessary condition can occur before the sufficient or at the same time. Take this example:

Drivers License Age 16+

You turn 16 first, and then some time after that you get a drivers license. Turning 16 is necessary, and if you meet someone who has a driver's license, that is sufficient to prove that they are 16 or older. They might turn 16 on the same day they get their license, or they may wait 20 years to get it, but if they have the license you can infer that at some point they had their sixteenth birthday.

Rachael's post above expands on this. I wouldn't worry too much about the wording of the definition, just make sure you understand that the necessary condition is the thing that is required (i.e., it has to happen if the sufficient condition happens).

Hope that helps!
Beth