The argument concludes that history can tell us about the presuppositions of historians, which can be true whether those historians have the same presuppositions or entirely different presuppositions.

The argument isn’t concerned with whether we can figure out if historians are right about patterns in a specific case. Even if we could determine with certainty when historians are right and when they are wrong it could still be true that history as a whole tells us more about historians than about history.

The argument does not need details about what specific presuppositions historians might have, it is instead only about the fact that historians have presuppositions that in the first place and that history can tell us about them .

Whether or not historians could potentially be aware of their own presuppositions is not relevant to the claim that history tells readers about the presuppositions of those historians.

This fills the missing link in the argument. If this were negated, and the patterns imposed were not affected by presuppositions, then studying those patterns would not provide any information about the historian’s presuppositions and the conclusion would be undermined.’