I know the question has already been shortly answered on this website. But, I want to specifically know if Tarski's definition of truth is circular or valid? And if there is any convincingly non-circular definition out there.
It seems obviously circular to me, but it has been pointed out to me that it being circular is not the mainstream view.
We wish to prove the truth of a sentence in the object language (L), but we use a metalanguage (M) to do so, the definition is based around terms used in the sentence of L, but without the notion of "truth".
The whole thing seems circular. I mean not the definition of truth alone, but the usage of the words in the object language and the metalanguage, and the definition of truth taken together. Because, now the words in L are dependent on truth, and truth is now dependent on the same words M.
There is another issue which @Not_here has pointed out. The infinite regression between the meta languages on which to define the notion of truth on.