- #1
p3forlife
- 20
- 0
Hi, I have a question about proofs by contradiction in general. Without getting into the mathematical details, suppose we had the statement:
For every (condition A), B is true.
If we want to prove this by contradiction, we want to assume the negation of this statement, and then prove it to be false.
My question is, what is the statement we assume when we prove it by contradiction? Is it:
1. There exists a (condition A) such that B is not true.
2. For every (condition A), B is not true.
My guess is 1. But in this case, wouldn't it be hard to prove 1 by contradiction, because you are trying to prove a specific case to be false?
I usually have confusion with logic when "for every" and "there exist" crop up in statements. Then I'm not sure which "for every" and "there exist" to change to prove by contradiction or by contrapositive.
Thanks for your help!
For every (condition A), B is true.
If we want to prove this by contradiction, we want to assume the negation of this statement, and then prove it to be false.
My question is, what is the statement we assume when we prove it by contradiction? Is it:
1. There exists a (condition A) such that B is not true.
2. For every (condition A), B is not true.
My guess is 1. But in this case, wouldn't it be hard to prove 1 by contradiction, because you are trying to prove a specific case to be false?
I usually have confusion with logic when "for every" and "there exist" crop up in statements. Then I'm not sure which "for every" and "there exist" to change to prove by contradiction or by contrapositive.
Thanks for your help!