FiR: Errors of Composition vs. Exceptional Case

[165OrBust]

Hello PS Community,

Under the Flaw in Reasoning question type, I’m having trouble differentiating between Errors of Composition (“when the author attributes a characteristic of part of the group to the group as a whole” - LR Bible, p. 517) and Exceptional Case (when the author “takes a small number of instances and treats those instances as if they support a broad, sweeping conclusion” - LR Bible, p. 504).

Is the difference as simple as the author using a noun/adjective “characteristic” vs. verb/event “instance”?

Any advice is welcome!
Liz

[Claire Horan]

Hi Liz,

I think it's unlikely that you would get a question wrong due to confusion over these two logical fallacies. If you do find such a problem, please post it!

Some errors in reasoning can be described accurately both as an error of composition and an exceptional case (also called an overgeneralization), but the terms are usually used in different contexts. For errors of composition, the part and the whole are usually fairly apparent. For example, you may have someone making an assumption about a whole class because they know something about one student in that class. The student is the part and the class is the whole. Or deciding that a whole movie is boring because one of the scenes is boring. The scene is the part and the movie is the whole.

Exceptional case/Overgeneralization is similar but is more often used in the context of data points. When a new technology becomes popular in Japan, for example, it would be overgeneralizing to assume that it will become popular somewhere else (because countries differ in lots of relevant ways). Here there is no obvious part or whole. This fallacy also often comes up when someone tells an anecdote or gives an example that applies to one person, then tries to draw a conclusion that the same thing will happen to others too.

I hope this helps!

[165OrBust]

Thanks Claire, that does help a bit - if nothing more than to confirm that I’m not completely out to lunch!

This question came from the Superprep Test A, section 1, question 21:

“Eugenia: Reliable tests have shown that Koolair brand refrigerators are the best-made of any of the other major brands because they last longer and, on the whole, require fewer repairs than do refrigerators of any other major brand.

Neil: That is impossible. I have owned refrigerators of several different major brands, including Koolair, and the Koolair needed more repairs than did any of the others.

The reasoning in Neil’s response is flawed because he:

C. (correct answer) rejects a generalization on the basis of a single negative instance when that generalization has reasonable support and is not universal.
E. concludes that what holds true of each member of a group taken individually must also hold true of that group taken collectively.”

I immediately went to answer C, hesitated after reading E, and then chose C because Neil only spoke of one instance (“a single negative instance”) and not many (“each member of a group”). But it piqued my interest and led me down the rabbit hole. Please let me know if I’m overthinking this - to be honest, I have bigger concepts to nail down (damn you LG!)!

Thanks again,
Liz

[Ben DiFabbio]

Thanks Claire, that does help a bit - if nothing more than to confirm that I’m not completely out to lunch!

This question came from the Superprep Test A, section 1, question 21:

“Eugenia: Reliable tests have shown that Koolair brand refrigerators are the best-made of any of the other major brands because they last longer and, on the whole, require fewer repairs than do refrigerators of any other major brand.

Neil: That is impossible. I have owned refrigerators of several different major brands, including Koolair, and the Koolair needed more repairs than did any of the others.

The reasoning in Neil’s response is flawed because he:

C. (correct answer) rejects a generalization on the basis of a single negative instance when that generalization has reasonable support and is not universal.
E. concludes that what holds true of each member of a group taken individually must also hold true of that group taken collectively.”

I immediately went to answer C, hesitated after reading E, and then chose C because Neil only spoke of one instance (“a single negative instance”) and not many (“each member of a group”). But it piqued my interest and led me down the rabbit hole. Please let me know if I’m overthinking this - to be honest, I have bigger concepts to nail down (damn you LG!)!

Thanks again,
Liz

Hi Liz,

I just wanted to jump in here and confirm that your reasoning for selecting answer choice (C) over (E) in this case is spot on, and this is a great example to illustrate the difference between the Errors of Composition and Exceptional Case fallacies.

Answer choice (C) captures the flaw in Neil's reasoning because Neil is generalizing based on his own experience, which he does not know to be representative of the group as a whole.

Answer choice (E) misses the mark because it would be impossible for Neil to conclude anything about the group based on "what holds true of each member" of that group, since Neil doesn't know what holds true for each member of the group! He only has a single data point (his own refrigerator) to work with. In this case, if Neil knew that each and every refrigerator made by Koolair was as defective as his, then it would not be fallacious to conclude that the group as a whole has this problem.

Keep up the good work!

Ben

[165OrBust]

Thank you, Ben! It all makes sense now - and seems so simple when you put it like that...

Liz