Sagal criticizes naturalistic epistemology genetically for falling short of the mission of justifying the sciences with "no circles and no gaps," and he outlines a program, essentially along the lines of Paul Lorenzen's constructive philosophy, which is intended to carry out that mission. I shall present some reasons for believing that the constructive program is unachievable. The answer which I shall then offer to Sagal's criticisms of naturalistic epistemology is based in large part upon the inevitability of curtailing our philosophical ambitions.