Now he that sees, perceives that he sees; and he that hears, that he hears; and he that walks, that he walks; and in every other case, in the same manner, there is some faculty which perceives that we are energizing; so that we perceive that we are perceiving, and understand that we are understanding. But this is the same as saying that we perceive or understand that we exist; for existence was defined to be perceiving, or understanding. Now, to perceive that one is alive, is of the number of those things which are pleasant in themselves: for life is a good by nature: and to perceive the good which is inherent in one's self is pleasant. But life is eligible, and particularly to the good, because existence is to them good and pleasant; for by the consciousness of that which is absolutely a good, they are pleased.

There is, however, a form of the fallibility principle which is both significant and acceptable. It holds that even one's most cherished and tenaciously held convictions might be false and are in principle always subject to rejection, reformulation, improvement, or reformation.

Think of a flabby person covered with layers of fat. That is what your mind can become — flabby, covered with layers of fat till it becomes too dull and lazy to think, to observe, to explore, to discover. It loses its alertness, its aliveness, its flexibility and goes to sleep. Look around you and you will see almost everyone with minds like that: dull, asleep, protected by layers of fat, not wanting to be disturbed or questioned into wakefulness. ¶ What are these layers? Every belief that you hold, every conclusion you have reached about persons and things, every habit and every attachment. In your formative years you should have been helped to scrape off these layers and liberate your mind. Instead your society, your culture, which put these layers on your mind in the first place, has educated you to not even notice them, to go to sleep and let other people — the experts: your politicians, your cultural and religious leaders — do your thinking for you. So you are weighed down with the load of unexamined, unquestioned authority and tradition.

But it is interesting that the same thing happens to you when you have to give some warrant for trusting in "reason". I noted your citation of LaPlace in your book and am glad you brought him up here. LaPlace believed he was not in need of the God hypothesis, just like you, but you should also know he held this position as a firmbeliever in celestial and terrestrial mechanics. He was a causal determinist, meaning that he believed that every element of the universe in the present was "the effect of its past and the cause of its future."

Just because your voice reaches halfway around the world doesn't mean you are wiser than when it reached only to the end of the bar.

Whereof one cannot speak, thereof one must be silent.

Our talk of external things, our very notion of things, is just a conceptual apparatus that helps us to foresee and control the triggering of our sensory receptors in the light of previous triggering of our sensory receptors. The triggering, first and last, is all we have to go on. In saying this I too am talking of external things, namely, people and their nerve endings. Thus what I am saying applies in particular to what I am saying, and is not meant as skeptical. There is nothing we can be more confident of than external things — some of them, anyway — other people, sticks, stones. But there remains the fact — a fact of science itself — that science is a conceptual bridge of our own making, linking sensory stimulation to sensory stimulation; there is no extrasensory perception.

The philosopher's task differs from the others', then, in detail; but in no such drastic way as those suppose who imagine for the philosopher a vantage point outside the conceptual scheme that he takes in charge. There is no such cosmic exile. He cannot study and revise the fundamental conceptual scheme of science and common sense without having some conceptual scheme, whether the same or another no less in need of philosophical scrutiny, in which to work. He can scrutinize and improve the system from within, appealing to coherence and simplicity; but this is the theoretician's method generally. He has recourse to semantic assent, but so has the scientist. And if the theoretical scientist in his remote way is bound to save the eventual connections with non-verbal stimulation, the philosopher in his remoter way is bound to save them too. True, no experiment may be expected to settle an ontological issue; but this is only because such issues are connected with surface irritations in such multifarious ways, through such a maze of intervening theory.

If one kept (as rock-bottom reality) the universe of the senses, aided by instruments and co-ordinated so as to form "science," then one would have to go much further — as many have since gone — and adopt a Behavioristic theory of logic, ethics, and aesthetics. But such a theory was, and is, unbelievable to me. I am using the word "unbelievable," which many use to mean "improbable" or even "undesirable," in a quite literal sense. I mean that the act of believing what the behaviorist believes is one that my mind simply will not perform. I cannot force my thought into that shape any more than I can scratch my ear with my big toe or pour wine out of a bottle into the cavity at the base of that same bottle. It is as final as a physical impossibility.

Much of the contemporary debate in the philosophy of mind is concerned with the clash between certain strongly held intuitions and what science tells us about the mind and its relation to the world. What science tells us about the mind points strongly towards some version or other of physicalism. The intuitions, in one way or another, suggest that there is something seriously incomplete about any purely physical story about the mind. For our purposes here, we can be vague about the detail and think broadly of physicalism as the view that the mind is a purely physical part of a purely physical world. Exactly how to delineate the physical will not be crucial: anything of a kind that plays a central role in physics, chemistry, biology, neuroscience and the like, along with the a priori associated functional and relational properties count as far as we are concerned. Most contemporary philosophers given a choice between going with science and going with intuitions, go with science. Although I once dissented from the majority, I have capitulated and now see the interesting issue as being where the arguments from the intuitions against physicalism — the arguments that seem so compelling — go wrong. For some time, I have thought that the case for physicalism is sufficiently strong that we can be confident that the arguments from the intuitions go wrong somewhere, but where is somewhere?