Trademark dilution is a cause of action for interfering with the uniqueness of a trademark.  However, even while legislatures have enacted more dilution laws over the past half century, many courts have been reluctant to enforce these new laws because although trademark owners think dilution is harmful, they have had difficulty explaining why.  Courts and commentators have now begun to use psychological theories, drawing on associationist models of cognition, to explain how a trademark can be harmed by the existence of similar marks even when consumers can readily distinguish the marks from one another.

Tushnet argues, however, that even though the cognitive theory of dilution is internally consistent and appeals to the authority of science, it does not rest on sufficient empirical evidence to justify its adoption.  Moreover, she argues that the harms it identifies do not generally come from commercial competitors but from free speech about trademarked products.  As a result, even a limited dilution law, in her view, should be held unconstitutional under current First Amendment commercial-speech doctrine.  In the absence of constitutional invalidation, this Article argues that the cognitive explanation of dilution is likely to change the law for the worse, and that given the empirical and normative flaws in the cognitive theory, using it to fill dilution’s theoretical vacuum would be a mistake.