An Experiment in Criticism is a 1961 book by C. S. Lewis in which he proposes that the quality of books should be measured not by how they are written, but by how they are read. To do this, the author describes two kinds of readers. One is what he calls the "unliterary", and the other the "literary". He proceeds to outline some of the differences between these two types of readers. For example, one characterization of an unliterary reader is that the argument "I've read it before" is a conclusive reason not to read a book. In contrast, literary readers reread books many times, savoring certain passages, and attempting to glean more from subsequent readings.