One of our goals when reading is to find and elucidate the key sentences in a book.
Independent of whether we agree with these key sentences, we first need to digest them — to capture the author's meaning. This is easier in non-fiction than fiction (in part, because typically non-fiction authors stick to the same definition throughout the book whereas fiction authors can change the meaning.)
Consider this beauty from Machiavelli's The Prince:
You must know there are two ways of contesting, the one by the law, the other by force; the first method is proper to men, the second to beasts; but because the first is frequently not sufficient, it is necessary to have recourse to the second. Therefore it is necessary for a prince to understand how to avail himself of the beast and the man.
Think for a second. What does it mean in your words?
In a long ago discussion between Mortimer Adler and Charles Van Doren, authors of The Classic Guide to Intelligent Reading, they dissect this quote.
Van Doren: That's a terrible statement isn't it? It means that in the way of life, in which we all live, we cannot afford to be wholly human, we also have to be beastual.
Most of the time, especially with expository books, it's easier to find the key sentences than to understand them.
We all read these sentences and feel as though we understand them. After all we understand the words the author is using. Adler however encourages us to go further. To demonstrate understanding he recommends putting the sentence in your own words. After you've done this, he suggests you offer a concrete example of the meaning.
Here is another example of this process playing out from Adler and Van Doren's conversation.
Adler: In the middle ages the great philosophers were very fond of saying, again and again, ‘nothing acts, except it is actual.' What does that mean to you? Say that in your own words now …
Van Doren: It means I can't be hurt by something that is only potential. Unless something actually is, it can't hurt me.
Adler: Unless something exists it can't hurt you. Show me you understand that by giving me a concrete example of something that can't hurt you because it isn't actual.
Van Doren: Well … a possible thunder storm can't wet me.
We've just added some insightful excerpts from Adler and Van Doren's fascinating conversation as bonus content to How to Read a Book. You don't want to miss this.