Flaw in the Reasoning: Errors in Composition and Division

[lawschoolforme]

Hi,

I have a question about something that appears on page 385 of the LRB.

Under the heading 'Errors of Composition and Division' are listed several examples of how this type of error might appear. The very first one gave me trouble:

"assuming that because something is true of each of the parts of a whole it is true of the whole itself"

I had a hard time time understanding why this would be a flaw in reasoning and couldn't quite think of a situation to help me understand this.

This concept ended up being tested in the "Question Type Training" book (Flaw #22) and I ended up missing the problem, so I just wanted to make sure I have a better grasp on this type of error before I miss such a type again! Thank you in advance for your help!

Sincerely,
lawschoolforme

[Dave Killoran]

Hi Lawschool,

A couple of things to consider here. First, note that the flaw is simply assuming that this is always the case. The problem is that you can't automatically do that. For example, consider this argument:

• "Every member of my team is a winner. Therefore the team is a winner."

Well, it could be true, but is it automatically true? No, because the nature of a collective whole can be different from the nature of each individual part.

Probably what's causing issues here is that in some cases, it is true. For example:

• "Each part of this chair is made entirely of plastic. Therefore, the chair is made of plastic."

So, because there are instances where it could be true, you have to evaluate what is occurring when you see it each time (which is true for most things on the LSAT, of course). The key is that in some cases the author just assumes that the parts and whole have an identical makeup, and that's not always the case.

Please let me know if that helps. Thanks!

[lawschoolforme]

That super helped! Cool. This makes sense now. Thanks so much!