Full Idea
There is no indication in Tarski's formal work of what it is that his various truth predicates have in common, and this is part of the content of the concept.
Gist of Idea
Tarski does not tell us what his various truth predicates have in common
Source
Donald Davidson (Truth and Predication [2005], 1)
Book Reference
Davidson,Donald: 'Truth and Predication' [Belknap Harvard 2005], p.27
A Reaction
This seems like a good question to raise. If I list all the 'red' things, I can still ask what qualifies them to all appear on the same list.