Than the existence of God all other things, even those which it seems to a man extravagant to doubt, such as his having a body, are less certain. Nor is there any reason sufficient to remove such doubt but such as presupposes the existence of God. From His existence it follows that our ideas or notions, being real things, and coming from God, cannot but be true in so far as they are clear and distinct. In so far as they contain falsity, they are confused and obscure, there is in them an element of mere negation (_elles participent du néant_); that is to say, they are thus confused in us because we ourselves are not all perfect. And it is evident that falsity or imperfection can no more come forth from God than can perfection proceed from nothingness. But, did we not know that all which is in us of the real and the true comes from a perfect and infinite being, however clear and distinct our ideas might be, we should have no reason for assurance that they possessed the final perfection--truth. Reason instructs us that all our ideas must have some foundation of truth, for it could not be that the All-Perfect and the All-True should otherwise have put them into us; and because our reasonings are never so evident or so complete when we sleep as when we wake, although sometimes during sleep our imagination may be more vivid and positive, it also instructs us that such truth as our thoughts have will assuredly be in our waking thoughts rather than in our dreams. _V.--WHY I DO NOT PUBLISH "THE WORLD"_ I have always remained firm in my resolve to assume no other principle than that which I have used to demonstrate the existence of God and of the soul, and to receive nothing which did not seem to me clearer and more certain than the demonstrations of the philosophers had seemed before; yet not only have I found means of satisfying myself with regard to the principal difficulties which are usually treated of in philosophy, but also I have remarked certain laws which God has so established in nature, and of which He has implanted such notions in our souls, that we cannot doubt that they are observed in all which happens in the world. The principal truths which flow from these I have tried to unfold in a treatise ("On the World, or on Light"), which certain considerations prevent me from publishing. This I concluded three years ago, and had begun to revise it for the printer when I learned that certain persons to whom I defer had disapproved an opinion on physics published a short time before by a certain person [Galileo, condemned by the Roman Inquisition in 1633], in which opinion I had noticed nothing prejudicial to religion; and this made me fear that there might be some among my opinions in which I was mistaken.