Extrinsic Aids to Reading
Extrinsic aids to reading are helps that lie outside the book itself: relevant experience, other books, commentaries, abstracts, dictionaries, encyclopedias, and reference works.
Adler's position is balanced. He does not ban these aids, but he resists dependence on them. The first task is intrinsic reading: work on the book itself with your own mind. Only after that should outside aids deepen, correct, or extend understanding. Otherwise the reader substitutes secondhand framing for first-order contact with the text.
The concept is useful because it explains both the value and the danger of summaries. A commentary can save time or rescue context, but it can also pre-chew the book so thoroughly that the reader never has to do the interpretive work himself.
This belongs near circle of competence because outside aids can legitimately widen your understanding, but only if you know where your unaided reading stops and borrowed support begins.