57. I must here call attention to the fruitfulness of the idea of being, which, combined with the idea of not-being, furnishes the idea of time. We have before seen, that the ideas of unity and number were favored in the same manner, and we shall soon have occasion to observe, how, from the ideas of being and not-being, spring others, which, although secondary in respect to these, are the most important of all the ideas which the human mind possesses. I call attention to this, from a desire that the reader may become accustomed to refer all ideas to a few points where they are united, not by a factitious chain imposed by arbitrary methods, but by the internal nature of things themselves. What extension is, in relation to sensible intuitions, the idea of being is, in relation to conceptions. The intuition of extension, and the idea of being, are the two fundamental points in all ideological and ontological science; they are two primitive data possessed by the mind, by means of which it can solve all problems, either in the sensible order, or in the purely intellectual. Regarded from this point of view, every thing becomes clear, and is arranged in the most logical order, because it is the order of nature. 58. I wish to make one observation on the method which I have followed in this work. I did not think it well to explain separately my opinion of these general connections of all ideas; for then it would have been necessary to treat philosophy in a systematic order, placing at the beginning what ought to be at the end, and trying to establish as a preliminary doctrine, what ought only to be the result of a collection of doctrines. To attain my object, it was necessary to go on analyzing in succession facts and ideas, without reference to system, without doing violence to them, in order to make them conform to a system, but only examining them, in order to ascertain their result. This, undoubtedly, is the best method. We thus obtain the knowledge of truth as a fruit of our labors on facts, and are not obliged to alter objects for the sake of forcing them to bend to the author's opinion. After the application which we have been making of the ideas of being, and not-being, to one of the most abstruse points of metaphysics, it is not out of place to call the reader's attention to this for a moment, so that he may be able to see the connection of doctrines. CHAPTER IX. PRESENT, PAST, AND FUTURE. 59. After explaining the idea of co-existence, we came to the definition of the various relations which time presents. They are principally three: present, past, and future. All others are combinations of these. 60. The present is the only absolute time: by this I mean, that it needs no relation, in order to be conceived. The present is conceived without relation to the past or to the future. Neither the past nor the future can be conceived without relation to the present.