A trademark is created when a new meaning is added to an existing word or when a new word is invented in order to identify the source of a product. This Article contends that trademark law fails in critical ways to reflect our knowledge of how words gain or lose meaning over time, and how new meanings become part of the public lexicon, a phenomenon commonly referred to as semantic shift. Although trademark law traditionally turns on protecting consumers from confusing ambiguity, some of its doctrines ignore consumer perception in whole or in part. In particular, the doctrine of trademark incapacity—also known as the de facto secondary meaning doctrine—denies trademark protection to a term that was once a generic product designation, even if consumers now see the term primarily as a source-signifying trademark.Analyzing trademark acquisition through the lens of semantic shift sheds light on how the trademark incapacity doctrine misunderstands both the nature of language and the role of consumer perception in shaping trademark’s competition policy. Courts and scholars suggest a generic term will rarely acquire source significance, and even if it does, there are competitive, conceptual, and administrative grounds for denying trademark protection. The standard account is mistaken: restriction of meaning—of which the change from a generic product designation to a source signifier is one example—happens frequently across time and across languages. In addition, understanding how and why restriction occurs highlights flaws in common justifications for trademark incapacity. This Article proposes replacing the doctrine of trademark incapacity with the primary significance test already applied at other stages of trademark litigation. If there is evidence that a majority of consumers have come to see the term as source-signifying rather than product designating, the law should recognize that source significance and the term should qualify for federal trademark protection.