Our talk of external things, our very notion of things, is just a conceptual apparatus that helps us to foresee and control the triggerings of our sensory receptors in the light of previous triggering of our sensory receptors.
To me, a philosopher who says that the distinction between human and nonhuman depends on whether you have a white or a black skin, and a philosopher who says that the distinction between human and nonhuman depends on whether or not you know the difference between a subject and a predicate, are more alike than they are unlike.