These assumptions are, according to Kant, quite different from the principles of the understanding. For the latter are grounds of the possibility of experience. We cannot deny them without making experience unmeaning. This cannot be said of the former. It obviously cannot be essential to experience that the multiplicity of the laws of nature should be reducible to unity, for such unity has never been discovered. Experience has been quite possible without it. This distinction between two kinds of principles Kant expresses by calling those with which we are now concerned regulative. The purpose they serve is the regulation and improvement of knowledge. They do not, like the principles of the understanding, prescribe to nature. We assume in them that nature is, in Kant’s words, purposive to the understanding--that is, we first think out what order of nature would be intelligible, and then look to see whether we cannot discover in nature such an order. This assumption does not prove that there is any such order, but in science we act as if it were there to be found out. This suggestion of Kant’s has been elaborated in many modern writers on philosophy, who have pointed out how much scientific method is governed by the notion of the most easily intelligible theory, and they have argued that science assumes, for the convenience of method, principles which it never completely proves. These principles are called sometimes methodological assumptions, sometimes postulates. The difference between such modern writers and Kant is that the former think that all a priori principles are of this nature, and that the principle of causation, for example, is itself only a postulate. The faculty of judgment, then, according to Kant, assumes for regulative purposes that nature is purposive to our understanding. What does this last phrase mean? We are often concerned to know the relation of things to our purposes. It has been pointed out that very many of our empirical concepts represent rather our practical interest in things than our desire to understand them as they are. Kant’s phrase implies that, apart from any such relation to particular purposes, there is a more general purpose of mere intelligibility, which some objects obviously serve more than others.