32 Next, there is “access-consciousness”33 of what one thinks, believes, or desires. We can verbally report these states, reflect on them and reason about them, and, to some extent, even control them. Such consciousness need not possess any phenomenal features. I may be conscious of my believing that F=ma, or of my CI-1033 chemical structure decision to buy one sort of toilet paper rather than another, but that consciousness does not require any qualitative features. Beliefs and decisions can perhaps be experienced in certain

ways, but if they have qualitative features at all, these are not essential to them. Furthermore, Inhibitors,research,lifescience,medical there is the questionable idea that consciousness and self-consciousness are the same. Mirror experiments show that great apes, elephants, and even bird species such as keas and European magpies can react purposefully to spots on their own bodies, and thus reveal a kind of self-recognition.34 Many animals do not pass the test, but we would not say that they are unconscious or that their sensations or feelings are devoid of qualitative features. These Inhibitors,research,lifescience,medical and other possible meanings of the term “consciousness”22,24 must be separated if one does not want to confuse what one aims to explain, or what one’s neuroscientific data are about. Problems of consciousness Inhibitors,research,lifescience,medical There is not merely one

philosophical problem that calls into doubt the possibility of a scientific treatment of consciousness. First, all problems depend on Inhibitors,research,lifescience,medical what we mean by “material states”—a question about which there is little clarity. The concept of matter has changed through history and will probably continue to do so.35 It is also controversial what constitutes a reductive explanation of phenomenological generalizations—about temperatures of gases, say—to microphysical laws—in this case, the kinetic theory of heat.36 Furthermore, with respect to all the aforementioned kinds of consciousness, we can ask whether they are reducible

to brain states or processes. Even when we focus on only one kind of consciousness, there are further distinctions to be made. For Inhibitors,research,lifescience,medical instance, it is one thing to ask (i) whether Tolmetin brain states are identical to qualia; and another (ii) whether it is possible to explain qualia in physicalist terms. We will see the importance of this distinction below. A short guide through major philosophical debates In what follows, the focus is on phenomenal consciousness alone, although some of the following considerations can be recast for other aspects of the mind. I present a number of influential skeptical arguments concerning reductive physicalism about qualia in an order from less to more plausible, each followed by the most straightforward and plausible replies (often somewhat simplified). Sometimes, I also mention counterreplies, thereby indicating that the critic of the skeptical argument needs to do better, by giving another reply or by addressing further skeptical arguments as well.