A central topic of the latest research in the philosophy of science is the question of what kind of relationship there is between the cognitive and social factors which underlie scientific knowledge. At present, this problem has manifested itself in a heated and still unfinished controversy between the proponents of artificial intelligence research and the sociologists of knowledge. By resolving the antagonism of these two positions, the book aims at developing a modular approach to an integrated philosophy of science which can handle the interaction between cognitive and social factors in a way which differs considerably from all current proposals.