36 THE HISTORY OF BIOLOGY 



proper have judged him far more sternly; they have realized far more clearly 

 the deficiencies in his system of thought, and the weaknesses inherent in its 

 structure. The idealistic philosophers have accused him of vitiating Plato's 

 theory of ideas, while adherents of critical philosophy have criticized his 

 dogmatic ideas of the universe. His extraordinary influence both on his con- 

 temporaries and on posterity, however, no one can deny. 



Form the true reality of matter 

 As a thinker Aristotle bases his system on Plato. According to Plato the ideas 

 of eternity are existing realities, of which the things of our earth are an im- 

 perfect image. Aristotle adopted the theory of ideas, but sought to overcome 

 the difficulty arising out of the questions how ideas are really related to 

 things and how they influence them, by placing ideas not outside things as 

 something independent and apart from their existence, but in things them- 

 selves. And he regarded the form of everything as its idea, as its true reality. 

 Form is the thing's reality, matter is a potentiality, to which form gives 

 reality. The bronze of which the statue is made is a potentiality; the form 

 which the sculptor gives it makes of the statue a reality. This method of 

 observation, derived from human life, Aristotle applies with inflexible con- 

 sistency to the whole of nature, both animate and inanimate. Thus the seed 

 is a potentiality out of which the germinating plant develops reality. The 

 same is true of the t^g and the embryo in relation to the creature which 

 develops therefrom. Consequently every lower stage of development is a 

 potentiality in relation to the higher stage of development which represents 

 its full realization. Thus we gtt a whole series of stages of development, be- 

 ginning with completely formless matter, which is an exclusive potentiality 

 without any reality at all, through inanimate nature, in which matter is 

 stronger than form, to the animate, in which form governs matter. Form in 

 living creatures is the soul, and the more highly developed it is, the more does 

 it control the corporeal matter. Plants have a lower kind of soul, which only 

 lives, but does not feel; animals possess a higher, sensitive soul, and, finally, 

 man has conscious reason. The means whereby form gives expression to its 

 dominance over matter is motion; all that occurs in the universe is motion, 

 and the more form-perfect the motion is, the higher the development it 

 represents. Our earth, therefore, with its manifold irregularities, is a lower 

 form of existence than the heavens, whose celestial bodies possess the most 

 perfect motion, circular motion. The heavenly bodies keep their position 

 and motion owing to their being enclosed in transparent spheres, one outside 

 the other. Thus they represent to the mind of Aristotle, as to that of Plato, 

 a higher form of existence than the earth with its creatures, including man, 

 and outside the outermost celestial sphere is the world of form free from all 

 matter, the highest intelligent existence, God, the fundamental origin of all 

 motion. Since, then, existence has its origin in a supreme intelligence, it is 



