The most obvious objection to eliminative materialism (EM) is that it denies obvious data, the very data without which there would be no philosophy of mind in the first place. Introspection directly reveals the existence of pains, beliefs, desires, anxieties, pleasures, and the like. Suppose I have a headache. The pain, qua felt, cannot be doubted or denied. Its esse is its percipi. To identify the pain with a brain state makes a modicum of sense; but it makes no sense at all to deny the existence of the very datum that got us discussing this topic in the first place. But Paul M. Churchland (Matter and Consciousness, rev. ed. MIT Press, 1988, pp. 47-48) has a response to this sort of objection:
The eliminative materialist will reply that that argument makes the same mistake that an ancient or medieval person would be making if he insisted that he could just see with his own eyes that the heavens form a turning sphere, or that witches exist. The fact is, all observation occurs within some system of concepts, and our observation judgments are only as good as the conceptual framework in which they are expressed. In all three cases — the starry sphere, witches, and the familiar mental states — precisely what is challenged is the integrity of the background conceptual frameworks in which the observation judgments are expressed. To insist on the validity of one's experiences, traditionally interpreted, is therefore to beg the very question at issue. For in all three cases, the question is whether we should reconceive the nature of some familiar observational domain.
Even if we grant that "all observation occurs within some system of concepts," is the experiencing of a pain a case of observation? If you know your Brentano, you know that early on in Psychology From an Empirical Standpoint he makes a distinction between inner observation (innere Beobachtung) and inner perception (innere Warhnehmung). Suppose one suddenly becomes angry. The experiencing of anger is an inner perception, but not an inner observation. The difference is between living in and through one's anger and objectifying it in an act of reflection. The act of inner observation causes the anger to subside, unlike the inner perception which does not.
Reflecting on this phenomenological difference, one sees how crude Churchland's scheme is. He thinks that mental data such as pains and pleasures are on a par with outer objects like stars and planets. It is readily granted with respect to the latter that seeing is seeing-as. A medieval man who sees the heavens as a turning sphere is interpreting the visual data in the light of a false theory; he is applying an outmoded conceptual framework. But there is no comparable sense in which my feeling of pain involves the application of a conceptual framework to an inner datum.
Suppose I feel a pain. I might conceptualize it as tooth-ache pain in which case I assign it some such cause as a process of decay in a tooth. But I can 'bracket' or suspend that conceptualization and consider the pain in its purely qualitative character. It is then nothing more than a sensory quale. I might even go so far as to abstract from its painfulness.
Now the existence of this rock-bottom sensory datum is indubitable and refutes the eliminativist claim. For this datum is not a product of conceptualization, but is something that is the 'raw material' of conceptualization. The felt pain qua felt is not an object of observation, but an Erlebnis, something I live-through (er-leben). It is not something outside of me which I subsume under a concept, but a content (Husserl: ein reeller Inhalt) of my consciousness. I live my pain, I don't observe it. It is not a product of conceptualization — in the way a distant light in the sky can be variously conceptualized as a planet, natural satellite, artificial satellite, star, double-star, UFO, etc. — but a material or object of conceptualization.
So the answer to Churchland is as follows. There can be no question of re-conceptualizing fundamental sensory data since there was no conceptualization to start with. So I am not begging the question against Churchland when I insist that pains exist: I am not assuming that the "traditional conceptualization" is the correct one. I am denying his presupposition, namely, that there is conceptualization in a case like this.
Most fundamentally, I am questioning the Kantian-Sellarsian presupposition that the data of inner sense are in as much need of categorial interpretation as the data of outer sense. If there is no categorization at this level, then there is no possibility of a re-categorization in neuroscientific terms.