The idea here is simple. If giving the LP either the value of "true" or the value of "false" results in an inescapable contradiction, we can avoid the Paradox by saying that the LP has neither value, thus preventing the contradiction. There are many arguable problems here. Firstly, this would seem to require abandoning the Law of the Excluded Middle or else the Principle of Bivalence. Now, I've no qualms with dropping Classical Logic in favor of a Non-Classical Logic, but I get the feeling many people would not like that. — MindForged
Do we have to abandon classical logic when we claim that the sentence "go away" is neither true nor false? — Michael
Hello,
I do not think that we have to abandon classical logic because of the "liar",
but I like playing around with non-classical logics.
One exotic logic is my favorite:
The "logic of reflection" by Ulrich Blau
which i developed and extended to an alternative logic, the "layer logic".
Link to the logic of Ulrich Blau:
https://ivv5hpp.uni-muenster.de/u/rds/blau_review.pdf
Link to "layer logic" "Trestone":
https://www.researchgate.net/post/What_do_you_think_of_layer_logic-and_the_use_of_a_new_dimension_to_come_around_contradictions
In layer logic a hierarchy of truth layers is used (similar to the hierarchy of types of Bertrand Russell).
Proposals to not have truth values any more,
but only proposals in connection with a layer have a truth value.
The liar statement here has the following form:
L:= For all n= 0,1,2,3,... "This statement is true in layer n+1 if it is not true in layer n and else it is false"
As all statements are u=undefined in layer 0,
we get for layer n=0:
"This statement is true in layer 0+1 if it is not true in layer 0 and false else"
Therfore: "This statement is true in layer 1"
For n=1: "This statement is true in layer 1+1 if it is not true in layer 1 and false else"
Therfore: "This statement is false in layer 2"
We see: The liar statement L is undefined in layer 0, true in layer 1,3,5,7,...
and false in layer 2,4,6,8,...
So the truth-value is alternating with the layers.
A classical statement would have only one truth-value in all layers 1,2,3,4,5,...,
so we can see, that L is a non-classical statement.
In layer logic it is not paradox, but an ordinary statement.
Layer logic is a little bit cumbersome,
but has amazing advantages:
Nearly all paradoxes can be solved similiar to the liar.
With layer logic a "layer set theory" can be defined,
where the diagonalization proof of Cantor is no longer valid
and where the Russell set and the set of all sets are ordinary sets.
Even natural numbers and an arithmetic can be defined.
A small set back: The prime factorisation of natural numbers could differ in layers.
But on the other hand it is probable, that the proofs of Gödel`s incompleteness theorems are valid no more.
Layer logic is a kind of a third way between classic logic and constructivistic/intuitive logic.
It is a logic with three truth-values, but the layers are the most important part.
Indirect proofs are allowed in layer logic, but only within a layer.
As in most classic proofs there are different layers involved if transformed to layer logic,
those indirect proofs are mostly not valid any more.
Unfortunately nobody up to now has seen a layer in reality,
but as long as the idea does not lead to contradictions it remains an interesting idea.
Yours
Trestone