No general features of the logic of falsifiability can assure, for every isolated empirical hypotheses H and independently of the domain to which it pertains, that H can always be preserved as an explanans of any emprical findings O whatever by some modification of the auxiliary assumptions A in conjunction with which H functions as an explanans. For Duhem cannot guarantee on any general logical grounds the deducibility of O from an explanans constituted by the conjunction of H and some revised non-trivial version R of A: the existence of the required set R of collateral assumptions must be demonstrated for each particular case.