We know directly and absolutely our own mental phenomena. After that, we have to start making assumptions. We have to assume that our memories really are memories and aren't simply presently experienced mental phenomena with echo sensations attached. Furthermore, we make the metaphysical assumption that there is an external world and the corresponding epistemic assumption that we can gather reasonably reliable information about that world via our senses. And we also assume that there are other minds and that we can again ascertain reliable information via observation of behavior and speech.

Having made those assumptions, why shouldn't we assume more and commit to the existence of an emotional world? When we say that when we're sad, we're actually perceiving an object called "a sad" (such as when sensing an apple, we're perceiving the object "an apple") or similarly when we're feeling happy, and so on and so forth. Why not also take this further and assume the existence of a fictional world. Why shouldn't we say that when we think of Santa Claus, we're actually perceiving an object in the fictional world known as "Santa Claus."? And also an arthimetic world as well? We think of three because we perceive the object "three".

What is it about the physical world that justifies our belief in it more than any other realm? What justifies the claims in an external physical world? And what justifies that claim any more than the claim that there is an external emotional world?