The facility of ordinary thinking is one of the unexplained marvels of psychology. There is no sign that we calculate before we speak, nor that we struggle to form our thoughts correctly. Normal thinking demands no special concentration and takes hardly any time. We do not have to sift through a mixture of logical and illogical or grammatical and ungrammatical thoughts. The mind is free to spend its energy on selecting the effective thought or the appropriate expression from the possibilities offered to it. There is not even any sign that as children we once were clumsy in our thinking, but have practiced the skill to the point where it has become automatic. The child's thoughts occur as abundantly as the adult's, and they spontaneously obey rules of form appropriate to his age. He moves as easily in that realm as we do in our own.