Full Idea
It seems reasonable to say that a truthmaker for a contingent truth is also a truthmaker for the truth that the contradictory of that truth is possible.
Gist of Idea
One truthmaker will do for a contingent truth and for its contradictory
Source
David M. Armstrong (Truth and Truthmakers [2004], 07.2)
Book Reference
Armstrong,D.M.: 'Truth and Truthmakers' [CUP 2004], p.84
A Reaction
The truthmaker will have to be not only some fact, but also the additional fact that it is contingent, in order to generate the possibility of the contradictory.