The First Amendment provides for specific rules that apply to “religion” without defining the term. This definition seems essential; the prohibition on establishment and the guarantee of free exercise apply by the law’s terms to religion, and not to anything that is not religion. Although Judge Adams in the epigraph seems to easily explain the distinction as one between mere “strongly held ideologies” on the one hand and “religion” on the other, it is not clear that such a distinction is actually possible. Black’s Law Dictionary, for example, qualifies every factor that it includes in its definition of religion, leaving nothing concrete in the concept. Black’s must use such a malleable definition because even among core religions—those beliefs that are unambiguously religious—there is significant diversity. When one expands the term beyond that core, the definition may become even murkier: some scholars have argued that the title of religion should extend to fitness clubs, television shows, or even sports fandoms. Despite Judge Adams’s conviction, it simply does not appear there is any essence of religion, with which a belief becomes religious and without which a belief cannot be religious.