Full Idea
The realist says that disposition ascriptions are ascriptions of real powers. This leaves unanswered the question, 'power to do what?' The problem of background conditions means that the realist cannot say what it is that a power is a power to do.
Gist of Idea
If dispositions are powers, background conditions makes it hard to say what they do
Source
Stephen Mumford (Dispositions [1998], 04.9)
Book Reference
Mumford,Stephen: 'Dispositions' [OUP 1998], p.88
A Reaction
It is hard to say what a disposition will do, under any other account of dispositions. I would take a power to be defined by a 'modal profile', rather than an actual account of what it will lead to.