Imagine you are the only person on earth, without anyone with whom to share your thoughts. More significantly, you have no one with whom to compare your thoughts and find them at odds. Imagine further that you either never need to revise your beliefs or that you would have no memory of the revision if you did. In such circumstances, what need would you have of a truth-predicate? What function would it serve? To what, and on what basis, would the predicate apply? What would constitute the contrast-class? These questions would remain were you to imagine yourself not alone but rather a member of a community for which believing in sympathy were assured. Without (relatively persistent) intra- and/or inter-personal doxastic discrepancy, truth would never be.
The lives we lead are replete with such counterpoised believing and means to distinguish, effectively and easily, such beliefs have developed. Those means essentially involve–indeed, are undoubtedly founded on–the introduction of the truth-predicate: the contents of one’s own (current) beliefs–what immediately constitutes, for each believer, ‘reality’–can always be identified by appending ‘is true’ to their (sincere) assertion. Believing, as the saying goes, is believing true.
Tracking doxastic conflicts is not the only service a truth-predicate might be called upon to perform. The truth-predicate is invaluable in enabling both indirect (i.e., ‘blind’) and compendious reference to belief-contents. Indeed, it might well be that the truth-predicate is essential for such endorsements, there being no other device in natural language adequate to the purpose. Yet these latter uses seemingly become pressing only in a context where doxastic conflict is possible. No speaker (or community) would need to make any endorsement, indirect or otherwise, if there were guaranteed uniformity of belief.
The truth-predicate, and so that notorious nominal, ‘truth’, are psychic solutions to an ongoing and insistent psychic difficulty: we have to settle the reality within which we each must act.