The human being is both a material and a spiritual being. He shares many qualities with other animals, but certain basic qualities make him distinct from them. Such qualities fall within three areas: 1. knowledge of the self and of the world, 2. desires which govern human beings, 3. the degree to which the human being is influenced by such desires. Knowledge of the world is achieved by man, as well as by other animals, through the senses. However, some animals are stronger in certain senses than man is. But sense knowledge is superficial. It does not go deep into the nature of things; nor does it enter the logical relationships that exist among things. In human beings, however, there exists another element which guides them to knowledge of the world and of themselves. Other animals are deprived of this. Only man can think.