Ross had been using his alphabetical card index "...almost since the beginning", however by October 1943 he had developed an initial outline for a book, and started using this category-oriented index to collect related concepts (see page 1497). This marked the start of the "Other Index", which he maintained in parallel to the original alphabetical index.
The "Other Index" is how Ross referred to this index on various cards in the alphabetical index. This index provides a view of the journal's contents based on the following 14½ categories: