General Claims and Their Contradictories & Some Valid and Invalid Forms

Week 9, Post 1

General claims lack a definite idea about all of part of a collection. A contradictory of a claim is the opposite truth of a claim. Using words such as "all" and "some," can change the meaning of a general claim to its contradictory claim.

In chapter 8, it states:
All means "Every single one, no exceptions" or "Every single one, and there is at least one."
Some means "At least one" or "At least one, but not all."

Claim:
All college students study for midterms.
Contradictory:
Some college students don't study for midterms.

Although an argument may sound good, it may not be in a valid form. Writing an argument directly, it is more likely to be a stronger argument. However, writing an argument backwards can make the argument weak or even invalid because it overlooks possibilities.

Direct way of reasoning with "all":
All dancers can count beats.
Juan is a dancer.
Therefore, Juan can count beats.

Arguing backwards with "all":
All dancers can count beats.
Juan can count beats.
Therefore, Juan is a dancer.

Juan does not have to be a dancer to count beats, he can be a musician. Arguing backwards limited the possibilities making the argument weak and invalid.