The following discussion is limited in scope and purpose. It is designed chiefly to provide some background information, as to certain key aspects, which will facilitate the reader's comprehension of the subject of this study-guide.

Any brief presentation such as this, while useful in itself, can also serve the broader purpose of better enabling the reader to pursue the subject further, in part by study of reference sources cited. This is a main aim of this study-guide.

References for all quotations and writings--citing the original sources--are listed in the Appendix.

Like the preceding Principles, separate parts of the following material will be consulted from time to time by various readers when occasion makes some particular topic of special interest for the moment, without having in mind the entire text. For this reason, there is some repetition of especially important points pertinent to different topics discussed, in order to insure adequate understanding of each of them separately--especially by the Young, as well as by others not familiar with the subject. The extremely few (if any) who will scan hastily this entire study-guide as a whole will, it is hoped, bear this in mind and be indulgent toward this aspect of the presentation in the following pages.