I had likewise in my own mind projected a third, the idea of which I owed to the observations I had made upon myself and I felt the more disposed to undertake this work, as I had reason to hope I could make it a truly useful one, and perhaps, the most so of any that could be offered to the world, were the execution equal to the plan I had laid down. It has been remarked that most men are in the course of their lives frequently unlike themselves, and seem to be transformed into others very different from what they were. It was not to establish a thing so generally known that I wished to write a book; I had a newer and more important object. This was to search for the causes of these variations, and, by confining my observations to those which depend on ourselves, to demonstrate in what manner it might be possible to direct them, in order to render us better and more certain of our dispositions. For it is undoubtedly more painful to an honest man to resist desires already formed, and which it is his duty to subdue, than to prevent, change, or modify the same desires in their source, were he capable of tracing them to it. A man under temptation resists once because he has strength of mind, he yields another time because this is overcome; had it been the same as before he would again have triumphed. By examining within myself, and searching in others what could be the cause of these different manners of being, I discovered that, in a great measure they depended on the anterior impressions of external objects; and that, continually modified by our senses and organs, we, without knowing it, bore in our ideas, sentiments, and even actions, the effect of these modifications. The striking and numerous observations I had collected were beyond all manner of dispute, and by their natural principle seemed proper to furnish an exterior regimen, which varied according to circumstances, might place and support the mind in the state most favorable to virtue. From how many mistakes would reason be preserved, how many vices would be stifled in their birth, were it possible to force animal economy to favor moral order, which it so frequently disturbs! Climate, seasons, sounds, colors, light, darkness, the elements, ailments, noise, silence, motion, rest, all act on the animal machine, and consequently on the mind: all offer a thousand means, almost certain of directing in their origin the sentiments by which we suffer ourselves to be governed. Such was the fundamental idea of which I had already made a sketch upon paper, and whence I hoped for an effect the more certain, in favor of persons well disposed, who, sincerely loving virtue, were afraid of their own weakness, as it appeared to me easy to make of it a book as agreeable to read as it was to compose. I have, however, applied myself but very little to this work, the title of which was to have been 'Morale Sensitive' ou le Materialisme du Sage.