- #36
VazScep
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I know this is from several months ago, but:Hurkyl said:Yes, I'll say vague -- I've never been impressed by any presentation of Zeno's arguments.
Compare with, say, the Liar's paradox, in which I can formally derive a contradiction:
If P is the statement "P is false", then we have:
P = T or P = F
P = T --> P = F
P = T --> P = T and P = F
P = F --> P = T
P = F --> P = T and P = F
P = T and P = F
This is a real paradox. It, and other similar paradoxes, are the reason why the usual formal logic is designed in such a way that statements cannot refer to themselves (even indirectly!)
Statements can refer to themselves. In theories of arithmetic, you can code all statements as Gödel numbers, so that statements are essentially capable of making assertions about other statements. A theorem known as the Fixed Point Theorem then shows that for any expressible property p, there is a statement which says "This sentence satisfies property p".
The liar's paradox is avoided because the property of being a true statement is not expressible in theories of arithmetic. This is known as Tarski's Theorem.