I am reading Graham Priest's In Contradiction (p.14) and he mentioned that the semantic rules of 'this sentence' and 'is True' overdetermine and underdetermine the Liar Paradox and its counterpart respectively.
What did he mean? He didn't elaborate on exactly what rules did he appeal to to make these assertions, but to me 'this sentence' just refers to (1) or (2), while the predicate refers to their truth values - what rules are there to discuss?
PS: For context, Priest is defending against opponents against his inference rule as detailed in this other question who are assuming truth value gaps.