When my biography of C. S. Lewis came out in 2005, I was inexperienced enough as a writer of trade books that I actually read most of the reviews. I have become wiser in my declining years, but I still often think of something I learned from that experience.

I remember one review in particular, which was not negative so much as airily dismissive. The reviewer treated my book as something without any real interest, and then went on to write at length about Lewis … using information he had gained from my book. And in some cases echoing judgments I had made. (I know this because the particular information and the particular judgments he employed were not found in earlier books on Lewis.) He assumed the mantle of a writer so knowledgeable about Lewis that he could toss my book aside, but apparently knew little about Lewis that he didn’t learn from me. 

Since I read that piece, I have been aware of the danger of using the task of reviewing to give a false sense of your own expertise. First of all, I have tried never to fall into that trap myself — it's easy to do if you’re not careful — and then I have kept my eyes peeled for further examples. It’s rather discouraging how often I see it. Typically it turns up in those (tragically few) journals that still publish extensive review-essays: the London Review of Books, the New York Review of Books, occasionally the Times Literary Supplement. You start reading one of these reviews and after a short time it becomes impossible to tell whether the writer is employing his or her own expertise or rather is cribbing from the book under review.

There ought to be some code of reviewing ethics that requires reviewers to let us know when they are writing things that they knew before they read the book under review and when they are paraphrasing and summarizing that book. Estimated percentage of the knowledge I exhibit in this review that I got from the book I’m reviewing: 73. That kind of thing. I haven’t done anything quite that specific, but at times I have said something along these lines: “Almost everything I know about this subject I learned from this book.” I wish this were a more common practice.