Linda says that, as a scientist, she knows that no scientist appreciates poetry. And, since most scientists are logic...

mprezzy December 25, 2019

Flawed Reasoning

I am trying to understand what is meant when the instructor in the video says that the flaw is that the principle rule is trying to make a contrapositive of the quantifier sentence. I do understand how the diagramming worked in this passage, and I am able to diagram it correctly but is the focus on the most statement? The most statement in both premises was changed into a some and the variables were switched. Is that the part that is being referred to as the contrapositive of the quantifier?

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SamA January 7, 2020

Hello @mprezzy,

I think I can clarify that.

We have the premise that no scientist appreciates poetry.
S - - - - -> not AP
AP - - - - > not S

And another premise that most scientists are logical.
S - -most - - L

We can conclude that some logical people are scientists.
L - - -some - - - S

I want to connect our two premises to see what conclusions we can draw.
L - - - -some - - - - S - - - - - - > not AP

Some logical people do not appreciate poetry. This would be valid, but this is not the conclusion made in the stimulus.

The author attempts to make a contrapositive of this valid conclusion. But, as expressed in the video, you cannot make a contrapositive of a qualifier statement.
AP - - - - - - -> not S - - X - - -> not L

The first part of this is correct, but the second half is not. It is true that appreciating poetry proves that one isn't a scientist. But not being a scientist doesn't make one illogical.

To express the flaw in terms that may be easier to understand, the argument simply makes a claim about a group that we have no information about. We have some info about logical people (some are scientists) and about art appreciators (none are scientists). Do you see any premises that I diagrammed that could lead to a conclusion of not L (illogical)? There aren't any.

Similarly, answer choice B gives us information about adults, but makes a conclusion about children.

mprezzy January 12, 2020

That was helpful. Thank you.

Ravi January 16, 2020

@mprezzy, let us know if you have any other questions!