That certain paper bills have monetary value, that Vladimir Putin is the president of Russia, and that Prince Philip is the husband of Queen Elizabeth II: such facts are commonly called ‘institutional facts’. IFF are, by definition, facts that exist by virtue of collective recognition. The standard view or tacit belief is that such facts really exist. In this paper we argue, however, that they really do not—they really are just well-established illusions. We confront realism about IFF with six criteria (...) of existence, three established and three less so but highly intuitive. We argue that they all tell against the existence of IFF. An obvious objection to IFF non-realism is that since people’s behaviour clearly reflects the existence of IFF, denying their existence leaves an explanatory gap. We reject this argument by introducing a variant of the so-called ‘Thomas Theorem,’ which says that when people collectively recognize a fact as existing, they largely behave accordingly, regardless of whether that fact really exists or not. (shrink)