What thelematology is. Before I turn to the guide to living rationally itself, it is necessary that I issue the doctrine of the human will as preparation in advance, without which one cannot possibly succeed in the following. For, since the guide to a rational life includes solely those rules that are prescribed to the will, and which must therefore be derived, for the most part, from the constitution of the will, it is easy to see that one must first know how the will is constituted and works by nature before one can sufficiently explain how it ought to be. One can justifiably call this doctrine thelematology or the doctrine of the will, a name by which I mean nothing other than a theoretical science of the properties, powers, and effects of the human will. The idea is therefore that we here seek out, as far as possible, the causes [4] of that which we perceive in the will through experience with the intention of learning to both better recognize and judge good and evil as well as promote the former and eradicate and hinder the latter. Why it is treated here. I believe that this is the correct place to treat this important subject. It is indeed known that many tend to include it in metaphysics. It seems to me, however, that this is not done correctly, in that metaphysics must without a doubt lose all determinate boundaries if one is also permitted to treat contingent truths in it, concerning which one has no assurance that they cannot be otherwise in a different world, and which one cannot know a priori on the basis of the necessary essence of a thing or of a world in general. Nonetheless, one can simply grant each scholar their own freedom on this matter.