How to Read a Book/ Part Two/ Chapter 12/ Aids in Reading.
Commentaries, essays, summaries, reflections, dictionaries, vocabularies, glossaries, encyclopedias, reference texts, etc. All of the previous mention "tools", damage more than they in fact "aid". Ideally one does not need any of these tools, particularly when handling a specific piece of literature. Furthermore, there are ways to approach the usage of dictionaries and encyclopedias for instance, a rule of thumb should be to know what you are looking for. It seems senseless to look inside a dictionary if you do not know what it is you are looking for, but to most this does not seem as apparent. When stumbling with the use of a word within a piece of writing, one tends to inquire to a dictionary, but as stated on previous chapters such is not needed at all, in fact it only conflicts with our understanding. When authors use specific words, its definition can and only will be find inside his work, unless the book is a bad one.
Before going further into the nature of reading aids ant the proper usage Adler commands us to apply, I would like to mention one advice that is given within the reading, one of many, that is very useful. "Read literature chronologically", I am paraphrasing of course, but reading literature in order truly makes a significance addition to ones understanding. Reading in such a way, allows one to compare books in their natural written history, and makes the experience much more fruitful Imagine, if you will comparing Euclid with Ptolemy, understanding Euclid will in essence pave way to understand Ptolemy.
Now, back o the use of all above mentioned tools. First things first, when approaching a reading no mater how hard the reading may seem to us, we should read it for ourselves, get the most of it by ourselves (with all the advice given since chapter 1 of this book), and only after doing so thoroughly, may one compare with external commentaries and summaries. Dictionaries and encyclopedias might be useful, in fact very useful, but one must also understand the structure and nature of those books; dictionaries have a sequence of words, words that may differ in meaning to how the author we are reading is using it, and encyclopedias primarily deals with facts. Knowing what we