(i) The book is sufficiently short for anyone who is interested to learn his way about it fairly quickly. (And the last part, FUNDAMENTAL STRUCTURE, has really nothing very much in it to be indexed except noughts and crosses.)
(ii) I have provided a considerable amount of cross-references in the text itself, so that a reader interested in one particular subject can without difficulty locate different passages dealing with that subject.
(iii) The third part itself, SHORTER NOTES, is already arranged under subject headings in the Pali alphabetical order, and a glance at the Table of Contents is enough to locate the article that is sought.
(iv) I have something of a feeling that an index would not be entirely in keeping with the character of the book. What I mean is this. Although the book is largely in the form of notes, and might therefore seem to be in the nature of a work of reference, it is actually intended to be read and digested as a single whole, with each separate note simply presenting a different facet of the same central theme. A person using the book as it is intended to be used would come, in the course of time, to regard it as an organic whole, with each part related to every other part, and would thus find an index an irrelevance. The presence of an index, on the other hand, might encourage a casual reader simply to refer to the word or subject of immediate interest to him and to neglect its essential relationship to every other part of the book. In a word, an index might make the book too easy. To find the meaning of any one single word in the book it is necessary to read the whole book.