Again, there is a kernel of truth here, as legitimate science does indeed build upon itself, but this philosophy was less than compelling because it left the problem of how to define progressive from degenerative research programs. He described four norms of scientific behavior, which remain useful as a description of good science, if not an ironclad method of detecting pseudoscience. Other methods have been proposed to demarcate science from nonscience, but none are perfect. What can be said is that such judgments are complex but there are legitimate criteria which can provide a pragmatic guide to the definition of science and the recognition of bad science, nonscience, and pseudoscience. There is clearly a continuum, with no unequivocal line of demarcation in the middle, but it is possible to recognize with high confidence enterprises which represent the two extremes of good science at one end and clear pseudoscience at the other.
Empiricism is the use of observation of the physical universe as a way to know about it.
The opposite approach is to try to divine truth about the universe just by thinking about, using pure logic, without recourse to direct observation. Empiricism is one of the founding principles of the modern scientific approach. In reality science philosophers cover the entire spectrum along this issue, with liberal essentialists and conservative nominalists meeting somewhere in the middle. It is important to recognize that even among extreme nominalists there are no philosophers who deny that nature provides some empirical data which influences or constrains ideas in science. This philosophy is known as materialism, and excludes the appeal to something outside the physical universe as an explanation for a physical phenomenon.