someone has succeeded in demonstrating that Dasein has been and will be for all eternity. As long as such a proof is still outstanding, this principle remains a fanciful contention which does not gain in legitimacy from having philosophers commonly 'believe' it.
Because the kind of Being that is essential to truth is of the character of Dasein, all truth is relative to Dasein's Being. Does this relativity signify that all truth is 'subjective'? If one Interprets 'subjective' as 'left to the subject's discretion', then it certainly does not. For uncovering, in the sense which is most its own, takes asserting out of the province of 'subjective' discretion, and brings the uncovering Dasein face to face with the entities themselves. And only because 'truth', as uncovering, is a kind of Being which belongs to Dasein, can it be taken out of the province of Dasein's discretion. Even the 'universal validity' of truth is rooted solely in the fact that Dasein can uncover entities in themselves and free them. Only so can these entities in themselves be binding for every possible assertion-that is, for every way of pointing them out.1 If truth has been correctly understood, is it in the least impaired by the fact that it is ontically possible only in the 'subject' and that it stands and falls with the Being of that 'subject'?
Now that we have an existential conception of the kind of Being that belongs to truth, the meaning of "presupposing the truth" also becomes intelligible. Why must we presuppose that there is truth? What is 'presupposing'? What do we have in mind with the 'must' and the 'we'? What does it mean to say 'there is truth' ? 'We' presuppose truth because 'we', being in the kind of Being which Dasein possesses, are 'in the truth'. We do not presuppose it as something 'outside' us and 'above' us, towards which, along with other 'values', we comport ourselves. It is not we who presuppose 'truth'; but it is 'truth' that makes it at all possible ontologically  for us to be able to be such that we 'presuppose' anything at all. Truth is what first makes possible anything like presupposing.
What does it mean to 'presuppose'? It is to understand something as the ground for the Being of some other entity. Such understanding of an entity in its interconnections of Being, is possible only on the ground of disclosedness-that is, on the ground of Dasein's Being something which uncovers. Thus to presuppose 'truth' means to understand it as something for the sake of which Dasein is. But Dasein is already ahead of itself in each case; this is implied in its state-of-Being as care. It is an entity for which, in its Being, its ownmost potentiality-for-Being is an issue. To Dasein's Being and its potentiality-for-Being as Being-in-the-world,
1 'Auch die "Allgemeingültigkeit" der Wahrheit ist lediglich verwurzelt, dass das Dasein Seiendes an ihm selbst entdecken und freigeben kann. Nur so vermag dieses Seiende an ihm selbst jede mögliche Aussage, das heisst Aufzeigung seiner, zu binden.'