But Empedocles’ interest in cosmology was only a part of his dominating interest in the organic world. He held some interesting evolution theories. His special interest in human physiology led him to frame the first theory of perception. Man is composed of the four elements, and he can know the universe around himself because Like in him attracts Like in the external world. The earth forms our solid parts, water the liquid parts, air is the vital breath, and fire is the soul. The blood contains the four elements, and is therefore the real carrier of life. If we perceive anything, it is because we have qualities similar to that thing. The element in us attracts the like element outside. He fancifully explained how parts of each element pressed upon parts of like elements――earth upon earth, air upon air; and how these clung together until sundered by Hate. The senses have only a partial number of elements, while the reason has them all; therefore sense knowledge is partial when compared with rational knowledge. =The Philosophy of Anaxagoras.= The pluralistic conception of the nature-substance, that was originated by Empedocles in this crude form, got a more complete character in the hands of Anaxagoras. For Anaxagoras took exception to the arbitrary assumption of Empedocles that the elements were only four in number. How could this world of infinite variety be derived from only four elements? We must postulate as many elements as there are qualities, if by merely shuffling them――by various combinings and separatings of them――their infinite number is to be explained. _There are a plural number of elements qualitatively distinct._ Every perceptual thing is composed of these heterogeneous parts or qualities or elements. But how do you know an element when you find one? Always by the fact that when you divide it, its parts are homogeneous. The elements are, therefore, those substances that divide into parts that are like one another; while the perceptual objects of nature can be divided into parts that are unlike one another. They are called “seeds” by Anaxagoras, and designated as “homoiomeriai” by Aristotle and later philosophy. This was a time, it must be remembered, when chemical analysis had not developed, and when mechanical division and change of temperature were the only means of investigation. Form, color, and taste were the characteristics that differentiated elements. So Anaxagoras was content to name as elements such things as bones, muscles, flesh, marrow, metals, etc. The countless elements or qualities are present in a finely divided state throughout the universe. Every perceptual object has present in it all elements, even opposite elements. It is, however, known and named by the element that prevails in it at any particular instant. For example, fire contains an element of cold but the fire element prevails. Opposites attract, and the qualitative change in a thing consists in