Dr. Watson’s view as to what is most certain is one which is in entire accordance with common sense. All psychological matters the plain man regards as more or less open to question, but he has no doubts about his office, his morning train, the tax-collector, the weather, and the other blessings of this life. It may amuse him, in an idle hour, to listen to some one playing with the idea that life is a dream, or suggesting that the thoughts of the people in the train are more real than the train. But unless he is a philosophical lecturer, he does not countenance such notions in business hours. Who can imagine a clerk in an office conceiving metaphysical doubts as to the existence of his boss? Or would any railroad president regard with favour the theory that his railroad is only an idea in the minds of the shareholders? Such a view, he would say, though it is often sound as regards gold-mines, is simply silly when it comes to a railroad: anybody can see it, and can get himself run over if he wanders on the tracks under the impression that they do not exist. Belief in the unreality of matter is likely to lead to an untimely death, and that, perhaps, is the reason why this belief is so rare, since those who entertained it died out. We cannot dismiss the common-sense outlook as simply silly, since it succeeds in daily life; if we are going to reject it in part, we must be sure that we do so in favor of something equally tough as a means of coping with practical problems. Descartes says: I think, therefore I am. Watson says: There are rats in mazes, therefore I don’t think. At least, a parodist might thus sum up his philosophy. What Watson really says is more like this: (1) The most certain facts are those which are public, and can be confirmed by the testimony of a number of observers. Such facts form the basis of the physical sciences: physics, chemistry, biology, anatomy, physiology, to mention only those that are relevant to the matter in question. (2) The physical sciences are capable of affording an explanation of all the publicly observable facts about human behaviour. (3) There is no reason to suppose that there are any facts about human beings that can be known only in some other way. (4) In particular, “introspection”, as a means of discovering by self-observation things that are in principle undiscoverable by observation of others, is a pernicious superstition, which must be swept away before any really sound knowledge of man becomes possible. (5) And, as a corollary, there is no reason to believe in the existence of “thought” as opposed to speech and other bodily behaviour.