This commentary to Nescolarde-Selva and Usó-Doménech’s (Reality, systems and impure systems. Foundations of Science 2013) links ideas in their paper to radical constructivism and raises two questions. (1) Would it be helpful to substitute the constructivist notion of viability for the traditional notion of truth with its connotations of relating language and reality? (2) Is the link made to issues in ontological philosophy important since the implicit constructivist epistemology of the paper considers mathematical ideas are just as real as ideas (...) about objects. (shrink)