A member of a residents' welfare body argues: 'Either we spend the entire maintenance fund this year on repairing the lift, or we accept that residents living on the upper levels will be left stranded. We cannot let residents be stranded. So the whole fund must go to the lift.' Which of the following is the principal weakness of this reasoning?

The argument works only if the two stated options exhaust the field, and they plainly do not: a partial repair, a staged payment or a smaller allocation would all keep the lift working without consuming the entire fund. Once a third possibility exists, rejecting the second option no longer forces the first. The size of the fund, the number of upper-level residents and the standing of the speaker leave the shape of the reasoning untouched.