Walton likens “Pegasus doesn’t exist” to “Pegasus. That didn’t work.” This in the dynamic tradition is called a test semantics: a big speech act is read as testing a smaller one against existing information. This chapter attempts a sneaky reinterpretation of Walton in which the smaller act is hypothesizing that a thing exists to check whether a falsehood follows. “Pegasus doesn’t exist” holds because there are truths φ such that if Pegasus does exist, then ~φ.