4.3 Does writing on a book seem wrong?
Obviously you have to take into account whether you own the text you are studying and, if so, whether you intend to keep it. Does it seem extravagant to write on a book and make it unfit for selling on? How important to you is selling it? Is it really a saving? If a book is important, why not assume you will keep it anyway? Then you can think of writing in it as an investment; you invest significant amounts of your time and mental energy in studying the book, in any case. If writing in it means you can quickly reconnect with the ideas and information you have studied, that investment is greatly enhanced. The marked-up book becomes an item in your personal system of knowledge. Part of this system is in your head and part on your bookshelf. Within the overall cost of studying, creating your own personalised versions of significant books can represent excellent value.
Underlining or highlighting words as you read is a powerful study technique:
it focuses your attention on the text;
it forces you to think about what the key concepts and issues are;
it leaves a record on the page of the meaning you found in the words as you read them.
When you return to a marked text you can quickly tune back in to those earlier thoughts – especially if you have written occasional comments in the margin.