@kennethamy,
kennethamy;128456 wrote:1. If you cannot know that you know unless you know, then knowing that you know is not a necessary condition of knowing.
2. You cannnot know that you know unless you know.
Therefore, 3. knowing that you know is not a necessary condition of knowing.
What reason is there for thinking that (1) is true?
---------- Post added 02-15-2010 at 06:28 PM ----------
Zetherin;128477 wrote:I think we would call this a contrary, not a contradiction.
A contradiction would arise, for instance, from these two propositions:
A.) I am in South Carolina.
B.) I am not in South Carolina.
Because no one can be both in South Carolina and not in South Carolina at the same time. More importantly, every person is either in South Carolina or not in South Carolina.
With contraries however, there is always a third option. In this case, the two propositions we have are:
A.) I am in Florida.
B.) I am in South Carolina.
But, it is possible that I could be in, for instance, Texas. That is, I could be in neither Florida or South Carolina. Therefore, it is a contrary.
I never heard a textbook talk about being a contrary and so far I have only reason to think that it is a word that you and fast use not everyone else.
I know of course of the relation of contrariness, which is not the same as your monadic property above. Is it some convoluted way of referring to the relation of contrariness?
I will just repeat myself. Per the
the broad definition of contradiction:
[INDENT]A proposition (or sentence or statement etc.) of the form P and not-P, or a proposition (or sentence etc.) from which a proposition (or sentence or statement etc.) of the form P and not-P is deducible.
[/INDENT]The sentence:
[INDENT]A. I am wholly in Florida and I am wholly in South Carolina.
[/INDENT]Is a contradiction because a strict contradiction is deducible from it, like this:
[INDENT]1. A. I am wholly in Florida and I am wholly in South Carolina.
2. If I am wholly in Florida, then it is not the case that I am wholly in South Carolina.
Thus, 3. It is not the case that I am wholly in South Carolina. (1, 2, simp. MP)
Thus, 4. I am wholly in South Carolina and it is not the case that I am wholly in South Carolina. (1, 3, simp, conj.)
[/INDENT]QED.
---------- Post added 02-15-2010 at 06:32 PM ----------
fast;126815 wrote:A: I'm in Florida
B: I'm not in Florida
C: I'm in Florida
D: I'm in South Carolina
A and B (CONTRADICTION): One must be true. One must be false.
C and D (CONTRARY): Neither must be true. Both can be false.
You are saying C and D is a contradiction, but it's not a contradiction, as it's not the case one of the two (C or D) must be true.
Depending on what you mean by "You are saying C and D is a contradiction", then you are right. See my post above. Maybe what you fail to grasp is this: The conjunction of any two contraries is a contradiction. Alone one proposition of a pair of contraries is of course not (normally at least if there is some counter-example where both contraries are contradictions in themselves) a contradiction.