XII. There is then in our mind something _a priori_ and absolute, which cannot be altered, even although all the impressions we receive from objects be totally varied, nor if all the relations we have with them were to undergo a radical change. BOOK FIFTH. IDEA OF BEING. CHAPTER I. IDEA OF BEING. 1. There is in our understanding the idea of being. Independent of sensations, and in an order far superior to them, there exist ideas in our understanding, which extend to, and are a necessary element of all thought. The idea of being, or of _ens_, holds the first rank among these. When the scholastics said that the object of the understanding was being, "objectum intellectus est ens," they enunciated a profound truth, and pointed out one of the most certain and important of all ideological facts. 2. Being, or ens in se, abstracted from all modification and determination, is, considered in its greatest generality, conceived by our understanding. Whatever may be the origin of this idea, or the mode of its formation in our understanding, certain it is that it exists. It is of continual application, and without it it is almost impossible for us to think. The verb _to be_, expressive of this idea, is found in every language: in every discourse, even in the simplest, we meet this expression: the learned and the ignorant, alike, continually employ it in the same sense, and with equal facility. The only difference, as to the use of this idea, between the rustic and the philosopher, is, that the one does, the other does not, reflect upon it: but the direct perception is the same in both, equally clear in all cases. Such a thing is or is not; was or was not; will be or will not be; there is something or nothing; we had or did not have; we shall have or shall not have, are all applications of the idea of being, applications made alike by all persons, without the least shadow of obscurity; all comprehend perfectly well the sense of these words, and the mind consequently has the idea corresponding to them. The difficulty, if any there be, begins with the reflex act, in the perception, not of being, but of the idea of being. So far as the direct act is concerned, the conception is so perfectly clear as to leave nothing to be desired.