3 ms·
My understanding is that for any system of axioms strong enough to encode arithmetic, you can have at most two of these three properties: 1. Complete (for any
by kerwioru9238492 4mo ago
My understanding is that for any system of axioms strong enough to encode arithmetic, you can have at most two of these three properties:
1. Complete (for any well formed statement, the axioms can be used to prove either it or its negation)
2. Consistent (can't arrive at contradictory statements ~ arriving at a both a statement and its negation )
3. The set of axioms is enumerable ~ you can write a program that lists them in a defined order (since the workaround for completeness can be just adding an axiom for the cases that are unproven in your original set)
If my understanding is correct, I believe your explanation is missing the third required property.
It's also important to point out that if we cant prove a statement or its negation (one of which must be true) then we know there are true statements that are unprovable. This is a much stronger of a finding than "Godel's first incompleteness theorem says that in any axiomatic system (sufficiently complex) there are theorems that are neither always true nor always false. "
- danbruc 4mo agoIt's also important to point out that if we cant prove a statement or its negation (one of which must be true) [...] Is that true, could it not be neither, i.e. independent of the axioms? Or is this assuming completeness which rules out independent statements?
- Epa095 4mo agoI just want to be a bit pedantic here (but this is logic after all...), and point out that in point 1 above you are talking about syntactical completeness, and not semantical completeness, which is the kind of completes Gödel proves in his first completeness proof. I think people are often confused because of this overloading of the word. And it is about sentences(a formula withouth free variables), not any well formed formula.