Trademark law centers its analysis on consumer confusion. With some significant exceptions, the basic rule of trademark law is that a defendant’s use of a mark is illegal if it confuses a substantial number of consumers and not otherwise. As a general matter, this is the right rule. Trademark law is designed to facilitate the workings of modern markets by permitting producers to accurately communicate information about the quality of their products to buyers, and therefore to encourage them to invest in making quality products in circumstances in which that quality wouldn’t otherwise be apparent. If competitors can falsely mimic that information, they will confuse consumers, who won’t know whether they are in fact getting a high quality pro...