It is such a principle that Kant speaks of sometimes as the synthetic unity of apperception, sometimes simply as understanding. For the reasons stated there seems no way of escape from the admission that it is, as he says, the basis of the necessary regularity of all phenomena in an experience: the basis, that is to say, not merely of our knowledge of uniform relations between phenomena, but of there being those uniform relations. The source of the relations, and the source of our knowledge of them, is one and the same. The question, how it is that the order of nature answers to our conception of it—or, as it is sometimes put, the question, whether nature really has, or having, will continue to have, the uniformity which belongs to it in our conception—is answered by recognition of the fact that our conception of an order of nature, and the relations which form that order, have a common spiritual source. The uniformity of nature does not mean that its constituents are everywhere the same, but that they are everywhere related; not that the thing which has been is that which shall be, but that whatever occurs is determined by relation to all that has occurred, and contributes to determine all that will occur. If nature means the system of objects of possible experience, such uniformity necessarily arises in it from the action of the same principle which is implied in there being any relation between the objects of experience at all. A relation not related to all other relations of which there can be experience, is an impossibility. It cannot exist except as constituted by the unifying subject of all experienced relations, and this condition of its possibility implies its connexion with all other relations that are, or come to be, so constituted. Every real relation, therefore, that is also knowable, is a necessary or objective or unalterable relation. It is a fact of which the existence is due to the action of that single subject of experience which is equally, and in the same way, the condition of all facts that can be experienced; a fact which thus, through that subject, stands in definite and unchangeable connexion with the universe of those facts, at once determining and determined by them. (§ 33 ¶ 1)