In this chapter I have brought together some critical reflections on the work of some of my colleagues in the field. I shall discuss first Stegmüller's conception of the problem and the criterion of empirical significance in scientific languages. Then I shall reflect critically on Popper's Logic of Scientific Discovery and Hempel's explanation of scientific laws. In a third section I plan to say something about Kuhn's The Structure of Scientific Revolutions. Section 4 will be concerned with Lakatos' methodology of scientific research programs. In Section 5 I shall turn to Hübner's Critique of Scientific Reason,and particularly to his conception of the nature of scientific theories. Finally, I shall make an effort to compare my own view of the nature of the natural sciences with that of Patrick Heelan.