The phrase "assumed reason" is correct and usable in written English.
It can be used when discussing a reason that is taken for granted or accepted without proof in a particular context.
Example: "The assumed reason for the delay was the bad weather, although no official explanation had been provided."
Alternatives: "presumed cause" or "taken-for-granted reason".
The assumed reason was that China will have joined their ranks by 2050 and does not want to meet such a target.
The assumed reason is that if everybody knew what everybody got paid, then all hell would break loose.
The assumed reason for this is the ongoing cold war between Mayor Bill de Blasio and the police union, but that is the wrong explanation.
This was also the assumed reason for failure of virus isolation.
The assumed reasons, according to the press, question the strategic role of manned fighter aircraft rather than the Gripen specifically, and the possible relevance of alternatives such as UAVs, surface-to-air missiles, or cyberwarfare capabilities.
With respect to the femoral vein approach, none of the commonly assumed reasons for limited Qa via the arterial line of an axial dual-lumen catheter could be confirmed.
Study outcomes should be carefully analyzed, possibly leading to further adjustments of the intervention protocol or to a second trial that is ruling out the assumed reasons for inconclusive results like a high rate of intercurrent diseases.
Third, our reasons for respecting something are, we logically have to assume, reasons for other people to respect it (or at least to endorse our respect for it from a common point of view).
They were being law-abiding and there was, they assumed, no reason why they should be penalised.
But few assumed the reason it would be meaningless: because the Colts' playoff spot had already been clinched.
The documents he requested were almost always provided, he said, and when they were not he assumed the reason was that the F.B.I. needed to protect an informer.
