I edited all that out. I wrote it too quick. I just don't think that we should infer that there were red cars in my driveway this morning just because I said that I ate every red car in my driveway this morning.

You would just be saying something silly, then, and didn't really mean it.

But if someone says, "I ate all my pancakes this morning," that would imply there were once pancakes this morning. There are now no longer any pancakes because the person ate them.

But, isn't it true that you ate every single pancake on your plate this morning? So what that there were no pancakes on your plate! You still ate everyone that was there (!), so the statement "I ate all my pancakes this morning" doesn't necessarily imply that there were once pancakes on your plate this morning.

Facts vs assertions of facts.

The proposition "there is a cat on the mat" is true if there is in fact a cat on the mat; likewise, the proposition "Kennethamy has a sister" is true if Kennethamy in fact has a sister. I'm okay with that,

I started to say if and only if, but I don't understand the necessity of adding "only."

It seems to me that if there is a cat on the mat, then the proposition "a cat is on the mat" is true. I don't deny that "only if" is correct. I'm just not sure why "if" isn't.

The proposition "there is a cat on the mat" is true if there is in fact a cat on the mat; likewise, the proposition "Kennethamy has a sister" is true if Kennethamy in fact has a sister. I'm okay with that,

I started to say if and only if, but I don't understand the necessity of adding "only."

It seems to me that if there is a cat on the mat, then the proposition "a cat is on the mat" is true. I don't deny that "only if" is correct. I'm just not sure why "if" isn't.

You are right, and I wrong. I misread what you wrote, sorry.

but what I am not okay with is the idea that you think he's expressing that proposition when he says his sister isn't fictional. You think that he is expressing (in part) the proposition that he has a sister and that his sister isn't fictional.

It's both. True propositions are biconditional.

"P" is true if and only if P.

If "the cat is on the mat" is true, then there is, in fact, a cat on the mat.
If there is, in fact, a cat on the mat, then "the cat is on the mat" is true.



What does that even mean if it means anything at all?? "Kennethamy's sister is not fictional." Would you please tell what proposition he is expressing? The burden is on you to tell everyone. Quite honestly, I can't formulate that proposition logically at all, since, when I do, I end up admitting Ken's sister exists. No wonder I thought he was implying he had a deceased sister!! If he wasn't implying that, then he was just talking nonsense. This is also nonsense: "Santa Claus is not fictional."

(Ex) Sx and ~Fx.

I really do have a brother. None of my brothers are fictional. When I say,
"My brother is not fictional," I am saying "I have a brother and he is not fictional."

(Ex) Brother(x) and ~Fictional(x)

or

(Ex) ~Fictional(x)

"There is something not fictional."

I can say pointing, "That car is not red," meaning, "there is a car and that car is not red."

(Ex) Car(x) and ~Red(x)

or

(Ex) ~Red(x)

"There is something not red."

---------- Post added 05-03-2010 at 10:42 PM ----------

Why always make a logical mess of things?

If we wanted to deny the truth of "Santa Claus is fictional" or deny the truth of "Santa Claus is not fictional," it is much more sensible to say,

"It is not the case there is a Santa Claus that is fictional,"

~Ex (Sx and Fx)

or, "It is not the case there is a Santa Claus that is not fictional,"

~Ex (Sx and ~Fx)

When we try to negate or assert the predicate "fictional" of Santa Claus, we end up admitting Santa Claus exists, Ex (Sx and ~Fx) or Ex (Sx and Fx). Big problem!

Doesn't X is not fictional, or X is not a fiction just mean, something is X? E.g. "You don't believe that I have a sister? Let me tell you that Joan is not a fiction!". That is, "Someone is Joan, and Joan is my sister".

This is all my fault.

Earlier in the thread, you said, "My sister does not exist, but she is not fictional." I thought that meant that she had no properties; thence, I came to the conclusion that you have no (nor ever had a) sister.

My apologies.

No need, and you are right, I have no sister. So, therefore, my sister has no properties. That is vacuously true, of course. The way "I ate every vegetable on my plate" is true because there were no vegetables on my plate to begin with.

That's just as vacuously true as saying,

"If I have a sister, then she is not fictional."

Why didn't you just say this?? It would have saved everyone so much trouble.

That's just as vacuously true as saying,

"If I have a sister, then she is not fictional."

Why didn't you just say this?? It would have saved everyone so much trouble.

I don't think that I quite understand that sentence.

Expound on why "Kennethamy's sister is not fictional" implies that Kennethamy has a sister. Does the logical rule you bring up always hold true?

Does "I ate every vegetable on my plate" imply that I once had vegatables on my plate?

I don't think that I quite understand that sentence.

Yes, it does logically imply that: that's why he needs "If I have a sister...." before it to make it true--vacuously true--otherwise, it's false.



In logic, you learn how to translate natural language sentences into logical form. And natural language can sometimes be ambiguous, too. So...

"I ate every vegetable on my plate" implies

"I ate."

There is something that ate. Ex Eat(x)

And if someone says, "Vegetables were what I ate" this logically implies,

"There is something I ate," namely, vegetables. Ex Vegetables(x)

---------- Post added 05-04-2010 at 09:47 AM ----------



"Kennethamy has a sister" is false. It makes the statement vacuously true under any truth-interpretation of "his sister is not fictional."

So, "If Kennethamy has a sister, then his sister is not fictional" is true.

I ate every vegetable on my plate does not imply that something was a vegetable on my plate, although it certainly suggests it. All the things I ate were vegetables does not have existential import any more than any universal proposition does. Universal propositions do not have, but particular propositions do have, existential import under the modern (Boolean) understanding of predicate logic. But I don't believe we are really disagreeing. The logical form of a universal proposition is hypothetical, so we agree. No real dispute between us.

This is so hurting my head.

Scenario 1: the facts: I did not eat.

Proposition1: I ate every vegetable on my plate this morning.
Proposition2: I ate
Proposition3: There were vegetables on my plate.

P1: true
P2: false
P3: Unknown (either true or false)

Scenario 2: the facts: I did eat from my plate. I ate everything on my plate. There never were vegetables on my plate. I ate no vegetables.

Proposition4: I ate every vegetable on my plate this morning.
Proposition5: I ate
Proposition6: There were vegetables on my plate.

P4: true
P5: true
P6: false

I think proposition 4 is true. Kennethamy thinks proposition 4 is true. Does Extrain think proposition 4 is true? You clearly think P1 is false, but that is a different proposition.

If I solve this, I may be able to confirm whether or not you're always (or only sometimes) using "nonexistent" to be the same as "fictional." [don't ask how].