Psychology helps to measure the probability that an aim is attainable.

Human beings are accustomed to think of intellect as the power of having and controlling ideas and of ability to learn as synonymous with ability to have ideas. But learning by having ideas is really one of the rare and isolated events in nature.

Amongst the minds of animals that of man leads, not as a demigod from another planet, but as a king from the same race.

The real difference between a man's scientific judgments about himself and the judgment of others about him is he has added sources of knowledge.

Some statements concern the conscious states of the animal, what he is to himself as an inner life; others concern his original and acquired ways of response, his behavior, what he is an outside observer

The dog, on the other hand, has few or no ideas because his brain acts in coarse fashion and because there are few connections with each single process.

This growth in the number, speed of formation, permanence, delicacy and complexity of associations possible for an animal reaches its acme in the case of man.