 If I assert that my dog is a reptile, then I’ve asserted something false—though in this case there are other things that are reptiles. If I assert that my dog is a unicorn then again I’ve asserted something false—though in this case there’s nothing in the actual world to which I could attach the predicate “… is a unicorn” and end up with a true assertion. The error theorist thinks that employing moral discourse is rather like talking about unicorns, though in the case of unicorns most people now know that they don’t exist, while in the case of moral properties most people are unaware of the error. To be an error theorist about unicorns doesn’t require that you think unicorns are impossible creatures; it’s enough that you think that they simply don’t actually exist. In the same way, to be a moral error theorist doesn’t require that you think that moral properties couldn’t possibly exist; it would be enough to think that they are never actually instantiated. (Note that there may be a difference between saying “Property P is never actually instantiated” and “Property P doesn’t exist,” but that’s a problem for metaphysicians to sort out. Holding either view with respect to moral properties is enough to make one a moral error theorist.)