“The Law of Exercise is that: Any response to a situation will, other things being equal, be more strongly connected with the situation in proportion to the number of times it has been connected with that situation and to the average vigour and duration of the connections.” We may sum up these two laws, roughly, in the two statements: First, an animal tends to repeat what has brought it pleasure; second, an animal tends to repeat what it has often done before. Neither of these laws is at all surprising, but, as we shall see, there are difficulties in the theory that they are adequate to account for the process of learning in animals. Before going further there is a theoretical point to be cleared up. Thorndike, in his first law, speaks of satisfaction and discomfort, which are terms belonging to subjective psychology. We cannot observe whether an animal _feels_ satisfaction or _feels_ discomfort; we can only observe that it behaves in ways that we have become accustomed to interpret as signs of these feelings. Thorndike’s law, as it stands, does not belong to objective psychology, and is not capable of being experimentally tested. This, however, is not so serious an objection as it looks. Instead of speaking of a result that brings satisfaction, we can merely enumerate the results which, in fact, have the character which Thorndike mentions, namely, that the animal tends to behave so as to make them recur. The rat in the maze behaves so as to get the cheese, and when an act has led him to the cheese once, he tends to repeat it. We may say that this is what we mean when we say that the cheese “gives satisfaction”, or that the rat “desires” the cheese. That is to say, we may use Thorndike’s “Law of Effect” to give us an objective definition of desire, satisfaction, and discomfort. The law should then say: there are situations such that animals tend to repeat acts which have led to them; these are the situations which the animal is said to “desire” and in which it is said to “find satisfaction”. This objection to Thorndike’s first law is, therefore, not very serious, and need not further trouble us. Dr. Watson considers one principle alone sufficient to account for all animal and human learning, namely, the principle of “learned reactions.” This principle may be stated as follows: _When the body of an animal or human being has been exposed sufficiently often to two roughly simultaneous stimuli, the earlier of them alone tends to call out the response previously called out by the other._