ABSTRACT
Mach and Poincare held similar views. James's thesis of Pragmatism was that a concept was true if it could be successfully used, but he did not attribute to it truth in any other sense. According to Vaihinger:
We have repeatedly insisted above that the boundary between truth and error is not a rigid one, and we were able ultimately to demonstrate that what we generally call truth, namely a conceptual world coinciding with the external world, is merely the most expedient error.4
