54. We shall understand the whole question much better, if we examine for a moment the meaning of co-existence. Two beings co-exist, or exist at the same time, when there is no succession of one to the other, when both exist, when there is not the existence of one and the negation of the other. In order to conceive co-existence, we need only conceive the existence of two beings: we form the idea of succession, by combining with the idea of the existence of one the idea of the negation of the other. The co-existence of two beings is their existence; their succession is the being of one, and the not-being of the other. Being refers only to the present; the past and the future are not being. That only is which is, not that which was, or which will be. There is a profound truth, a sound philosophy, and an admirable ontology in those words of the sacred text: "I AM WHO AM. He who is, hath sent me to you." 55. Without being and not-being, there is no succession, there is no time, there is only the present, there is eternity. To a being immutable in itself, and in all its acts, one in its intelligence, one in its will, always its own object, unchangeable, in the plenitude of its being, without any kind of negation,--to such a being there is neither _before_ nor _after_; there is only _now_. If you give to it the succession of instants, you apply to it, without any ground, the work of your imagination. Reflect well on the meaning of _before_ and _after_, in that which can change in nothing, by nothing, and for nothing, and you will see that succession is in this case a word without any meaning. We attribute to it succession because we judge the object by our perceptions, and our perceptions are successive; they have an alternative of being and not-being, even when applied to an immutable object. 56. Every one may experience this in his own mind. Conceive two beings to exist; add to this thought nothing accessory, neither the negation of being, nor of time, nor of any thing else,--merely conceive the existence of two beings, and see if any thing is wanting to complete your idea of their co-existence. If, on the contrary, you wish to perceive succession, or difference of instants, you must perceive the existence of one, and the negation of the existence of the other. Therefore, the idea of co-existence is simple, and implies only the existence of the beings, but the idea of succession is composed of the combination of being with not-being.