Mathematics has been the primary tool for scientists to describe the reality in which we live. However, describing something in mathematics does not mean it is true in reality. If we wish to pursue the concept of mathematics' decent from philosophy, then we know that existence is not a predicate and cannot be part of the concept of something. This Law of Philosophy (and by decent, mathematics) holds that just because something exists mathematically (a consept), does not mean that it also exists in reality. Unless we want to debate mathematics' decendance from philosophy and logic.
So in the spirit of the origional topic: String theory should be considered a hypotheses (in physics, not neccessarily mathematics), as it has not the scientific exidence to make it a Theory.
Though I would like to raise another point: a string theorist once told me that it (string theory) predicts gravity, and that can be used as evidence. any combats to this idea?