The alphabetical arrangement is very convenient when the chronological and geographical arrangements are unsuitable. There are documents, such as the sermons, the hymns, and the secular songs of the middle ages, which are not precisely dated or localised. They are arranged in the alphabetical order of their incipit—that is, the words with which they begin.
The systematic order, or arrangement by subjects, is not to be recommended for the compilation of a Corpus or of regesta. It is always arbitrary, and leads to inevitable repetition and confusion. Besides, given collections arranged in chronological, geographical, or alphabetical order, nothing more than the addition of a good table of contents is needed to make them available for all the purposes which would be served by a systematic arrangement. One of the chief rules of the art of Corpus and regesta-making, that great art which has been carried to such perfection in the second half of the nineteenth century, is to provide these collections, whatever the grouping adopted, with a variety of tables and indexes of a kind to facilitate the use of them: incipit tables in chronological regesta which lend themselves to such treatment, indexes of names and dates in regesta arranged by order of incipit, and so on.
Corpus and regesta-makers collect and classify for the use of others documents in which, at any rate in all of which, they have no direct interest, and are absorbed in this labour. Ordinary workers, on the other hand, only collect and classify materials useful for their individual studies. Hence certain differences arise. For example, the arrangement by subjects, on a predetermined system, which is so little to be recommended for great collections, often provides those who