This volume is dedicated to Mario Bunge in honor of his sixtieth birthday. Mario Bunge is a philosopher of great repute, whose enormous output includes dozens of books in several languages, which will culminate with his Treatise on Basic Philosophy projected in seven volumes, four of which have already appeared [Reidel, I 974ff. ]. He is known for his works on research methods, the foundations of physics, biology, the social sciences, the diverse applications of mathematical methods and of systems analysis, and more. Bunge stands for exact philosophy, classical liberal social philosophy, rationalism and enlightenment. He is brave, even relentless, in his attacks on subjectivism, mentalism,