Without the scientist there is no science; but science cannot, without inconsistency, admit the existence of the scientist; for the scientist is a man, and a man is not to be explained if feeling is ignored; and feeling is outside the domain of science. Science, however, in its claim to universal validity, is unwilling to recognize this; and a bastard entity has been brought into existence to make this claim seem valid. This bastard entity is sensation.
Imagine that, by accident, you rest your bare arm on a hot stove. You will undoubtedly lift your arm in a hurry. Why? Because contact with the hot stove is painful, you may say. But this won't do at all. What we want is an account of the changes that took place in your nervous system from the time your arm was rested on the stove to the time it was raised; and this account must be in strictly scientific terms. Pain, however, is not a scientific term. We can speak of an electrical or chemical impulse travelling along a nerve up your arm to your brain; for these are all things that can be publicly observed (in theory at least) by each one of a team of physiologists who are experimenting on you. But the pain you feel is strictly private: not even in theory can the team of physiologists observe it. (You can tell them that you feel pain, of course, but this does not make the pain public: what is public here is the sound of your voice, and the meaning of the words you utter is quite irrelevant—to allow that your words are meaningful is to beg the whole question.) A physiologist can observe an impulse moving up your arm, but he cannot observe a pain moving up your arm; only you can do that (if, for example, a red-hot needle is moved on your skin from the elbow to the shoulder; but not, of course, if your nerve is stimulated at a stationary point, when all you will feel is a stationary pain). This means (and I shall emphasize it by underlining it) that a physiologist must make no reference whatsoever to feeling (pleasure, pain, indifference) in his account of human behavior. If he fails to abstain he abandons scientific method.
But if we are to allow, as clearly enough we must, that feeling is capable of affecting the state of the nervous system (either by determining a specific action, such as raising the arm off a hot stove, or by conditioning a fairly lasting change in behavior), then we shall find ourselves obliged to abandon the postulate of the universal validity of the laws of science. So long as feeling depended upon the state of the nervous system and the state of the nervous system upon scientific determinism, all was well; but if, in addition, the state of the nervous system must be admitted to depend upon feeling, then (at least in the eyes of science) we enter the realms of chaos; for feeling, not being publicly observable, is not a scientific entity, and cannot therefore be governed by any laws of science, and the behavior of the nervous system, accordingly, ceases to be wholly rational. In short, the living body, and the nervous system in particular, are regions where the laws of science are manifestly less uniformly valid than elsewhere.
(Does an unconscious pain hurt? If you say 'yes', I ask 'how do you know, seeing that you are not conscious of it?' If you say 'no', I ask 'then how can you tell it is a pain and not a pleasant feeling?, how do you know there is any feeling at all?') This restriction of consciousness to rational thought is simply a prejudice of rationalism; and in the Buddha's Teaching it is specifically stated that consciousness (viññāna), feeling (vedanā) and perception (saññā) are inseparable—whenever there is any one of them there are all three. But to understand this a more subtle and intelligent approach to consciousness (or, more generally, to experience) is necessary.
The mistake is to approach consciousness by way of the body. But rational science, being essentially the study of what is public, namely matter, has no alternative. The laws of science are the laws of matter, and if these laws are universal then consciousness (whatever it may be) must necessarily be subordinate to matter. What science overlooks, and cannot help overlooking, is the fact that in order to know the body it is first necessary to be conscious of it—the body is an object (amongst other objects) of consciousness, and to seek to investigate consciousness by way of the body, instead of the other way round, is to put the cart before the horse. Consciousness comes first, and if it is to be known it must be studied directly (that is to say, by immediate reflexion).
(Those booklets that presume to explain the Dhamma on a scientific basis do the greatest possible dis-service to seriously interested enquirers. It is far better for a man to understand that he does not understand the Dhamma, than it is for him to believe falsely that he does understand it. The former attitude may encourage progress, the latter can only obstruct it.)