This thesis consists of two parts. In the first part a critique of the conceptual development of the Logical Empiricist and Popperian conceptions of scientific progress is presented. The major criticism made against them is that, contrary to fact, they require that successive scientific theories either contain or explicitly negate parts of each other.

In the second part an alternative conception of science is put forward in terms of which it is shown that incommensurability between theories is something other than the change of meaning of their individual terms, and that, in any case, such a change of meaning does not entail relativism. Furthermore this alternative conception, in seeing the relation between theories as being empirical rather than logical, avoids the major criticism of the Empiricist and Popperian views, while at the same time providing an account of how one of two theories can be a progression beyond the other.