3. Experience teaches this, but it can also be proved by conclusive arguments. All philosophers agree that the principle of contradiction is evident of itself to all men, that it needs no application, to understand the sense of the words sufficing; which could not be true did not all men have the idea of being. The principle is, that "it is impossible for a thing _to be_, and _not to be_ at same time." Here, then, is no question of any thing determinate; neither of body nor of mind, of substance nor of accidents, of infinite nor of finite, but of being, of a _thing_, whatever it may be, in its greatest generality; of which it is affirmed that it cannot both be and not be at the same time. Had we no idea of being, the principle would mean nothing: contradiction is inconceivable when we have no idea of the contradicting extremes, and here the extremes are _being_ and _not-being_. 4. The same is seen in another principle, closely resembling, if not identical with, that of contradiction: "every thing either is or is not." Here, also, there is question of being in its greatest indeterminateness, considered only as being, as nothing more. Without the idea of _being_, the axiom could have no meaning. 5. The principle of Descartes, "I think, therefore I am," also includes the idea of being: "I am." When he undertakes to explain it, this philosopher relies upon the fact that what is not, cannot act; thus the idea of being enters not only into the principle of Descartes, but is even the foundation upon which he rests it. 6. Whether we make the inward sense the basis of our cognitions, or prefer the evidence by which one idea is contained in another, it is always necessary to make the idea of being a primary element; we must suppose the understanding _to be_ before it can think; we must suppose thought _to be_ before we can make use of it; we must suppose our sensations and sentiments, the operations and affections of our souls, _to be_, before we can investigate their causes, their origin, and inquire into their nature; we must suppose ourselves _to be_, that _we are_, before we can advance one step in any sense. The idea of being does then exist in our mind, and is an element indispensable to all intellectual acts. CHAPTER II. SIMPLICITY AND INDETERMINATENESS OF THE IDEA OF BEING. 7. Nothing can be conceived more simple than the idea of being. It cannot be composed of elements. It allows of nothing determinate, since it is in itself absolutely indeterminate. The instant that something determinate is made to enter it, it is in a manner destroyed; it is no longer the idea of _being_, but of _such a being_; an idea applied, but not the idea of the being in all its generality.