I find myself in the unusual situation of having to improve for a second edition a book that I wrote forty years ago. Just as human beings always remain the same and unaltered in their core and that which is truly essential, while that which is superficial (that is, their appearance, manners, handwriting, style, tastes, ideas, views, insights, knowledge, etc.) undergoes great changes through the course of the years, so by analogy this brief work of my youth has remained completely the same in its essentials because the subject matter and content are as true today as they were then; however, I have improved its appearance, arrangement, and form as far as possible; it is nonetheless to be borne in mind that the improving hand is forty years older than that which wrote it, so the same problem, of which I have already had to complain in the second edition of the treatise on the principle of reason, cannot be avoided; specifically the problem that the reader is aware of two different voices, those of the old and of the young man, voices so clear that whoever has a sensitive ear never doubts which is speaking at any point. This, however, cannot be changed, and it is actually not my fault; rather, in the end it must be attributed to the fact that a venerated German public requires forty years to find out who would benefit by devoting attention to it.

I composed this treatise in the year 1815, whereupon Goethe kept the manuscript longer than I had expected because he took it along on the Rhine tour he made at that time, and for this reason the final preparations and printing were postponed so that the work first appeared at Easter 1816. – Since that time, neither physiologists nor physicists have found it worthy of consideration, but, undisturbed by it, they preach from the same text. Thus it is no wonder that fifteen years later it tempted a plagiarist (as a ‘snapper-up of unconsidered trifles’, Winter's Tale, p. 489) to turn it to his own use – which I have discussed more specifically in Will in Nature, first edn, p. 19 and second edn, p. 14.