25. These last observations explain another mark of corporeal substances. In the third chapter of this book we found the three characteristics of being, the relation of the permanent to the variable, and the subject of the variations; we now find a fourth, which is a negation, non-inherence in another. This negative characteristic is included in the positive one, _permanent subject of variations_; for it is clear that in conceiving a subject _permanent amid variations_ we do not include inherence, but rather deny it, at least implicitly. Non-inherence supposes something positive, something on which is founded the denial of the necessity of being inherent. What is this something? We know not. We know that it exists, but its explanation is beyond our reach. It is probably inexplicable without the intuition of the essence of things;--an intuition which we have not. CHAPTER V. CONSIDERATIONS ON CORPOREAL SUBSTANCE IN ITSELF. 26. The idea of substance, such as we have thus far explained it, implies a relation to accidents in general. The idea we are now examining is not that of an indeterminate substance, but of corporeal substance; and it must be confessed that it is difficult to conceive a particular corporeal substance without any accident. If I take from the paper, on which I am writing, its figure, extension, and all that relates to my senses, what is there left for me to conceive something particular and determinate, something which is not the idea of being in general, but of this being in particular? It is clear that, in order that the object may not disappear altogether, and losing its individuality be confounded in the universal idea, I must reserve something by which I can say _this_: that is to say, that which is here, or which has affected me in this or that manner, or has been the subject of such or such modifications. I consider at least its position with respect to other bodies, or its causality in relation to the effects which it has produced in me, or its nature as the subject of determinate accidents. Just as the idea of finite substance in general involves relation to certain accidents in general, the idea of a particular substance involves relation to particular accidents. 27. We find this relation in our mode of conceiving corporeal substance; we cannot assert that it is involved in the nature of the substance. This nature is unknown to us, and when we attempt to examine it, we pass to another question, that of the essence of bodies.