  In the Preface to the Metaphysical Foundations Kant (i) analyzes the concepts of nature and science so as to establish what conditions must be met for a body of knowledge to constitute natural science in the proper sense, (ii) explains why science so understood requires “a pure part” (4:469) and what criteria would have to be satisfied for such a pure part to exist, (iii) argues that chemistry and psychology cannot at present meet these criteria, and (iv) describes what procedure should be followed to satisfy these criteria and thus to provide the “pure part” that science proper requires.