The phrase "which presupposes" is correct and usable in written English.
You can use it when you want to imply that something has been taken as a given or assumed to be true in order to make a point. For example: "He argued that his suggestion was the best solution to the problem, which presupposes that he is familiar with the situation."
Leadership is a two-way street, a relationship which presupposes followers who consent to follow the leader.
Inside the interrogation room, the military's Code of Conduct, which presupposes adherence to the Geneva Conventions, was of little value.
Consumers, undoubtedly, win – but a strong and vibrant book culture, which presupposes the existence of bookshops, suffers as a result.
This is why in academia you must test your guess against the null hypothesis which presupposes your guess is wrong.
Its technique consists in depressing the value of life and distorting the picture of the real world in a delusional manner — which presupposes an intimidation of the intelligence.
The industry's current safety standards are based on a "thermal standard," which presupposes that radio frequency radiation too low to heat tissue is, by definition, safe.
But that clashed with NATO enlargement, which presupposed that Russia was a threat.
But that's unlikely to deter the sponsors of English-only measures, which presuppose that recent immigrants have resisted assimilation.
The result is that we go on having migration "debates" (more like shouting matches) which presuppose a world that simply doesn't exist.
"There was nothing in the young man's life which presupposed that he might be in be in—" "Of course not.
Accordingly, word classes such as adjective and preposition, which presuppose the existence of the noun phrase and prepositional phrase, are of equally doubtful validity.
