Historical Relations 99 



record of the past that was in the hands of a scholar of those days. 

 Written books with them were far less easy to obtain or to read 

 than are printed books with us, and the accumulation of what we 

 would regard as an adequate library was impossible. Thus great 

 progressive lines of study, such as philosophy or science, tended 

 to be represented only by their final development. The pur- 

 chasers of books naturally selected only the latest presentation. 

 Earlier versions, not being further multiplied, tended always to 

 disappear. So it comes about that in many departments of science, 

 e.g., astronomy, botany, medicine, the most completely represented 

 authors that have come down to us, Ptolemy, Theophrastus, 

 Galen, are the latest rather than the greatest, those who made the 

 final synthesis of knowledge rather than those who created that 

 knowledge. Because of this limitation our view of the development 

 of ancient science must necessarily be incomplete, while its final 

 synthesis can be sketched with confidence and in considerable detail. 



In the case of philosophy it happens that two very great figures, 

 Plato and Aristotle, fill the stage of the fourth century. Their 

 work, which has come down to us in considerable bulk, caused the 

 destruction of almost all that went before them. The history of 

 thought until their time has to be pieced together from hints and 

 fragments most of which are derived from their writings. For 

 these two writers, however, we are provided with the fullest 

 documentary material. 



The thought of Plato (427-347), like that of his master, 

 Socrates, was dominated by the ethical motive. Convinced like 

 his master that Truth and Good exist and that they are inseparable, 

 he embarked on an inquiry which had as its object to expose, 

 account for, and resolve into one comprehensive theory the dis- 

 crepancies of ordinary thinking. During this process he developed 

 a doctrine destined to be of great moment for the subsequent 

 relations of religious and scientific thought. It is the so-called 

 doctrine of ideas. 



The nature of this doctrine and the manner in which Plato 

 reached it has been briefly set forth by his pupil Aristotle. " In 

 his youth," says Aristotle, " Plato became familiar with the 

 doctrines (of certain philosophers) that all things perceived by the 

 senses are ever in a state of flux and there is no knowledge concern- 

 ing them. To these views he held even in later years. Socrates, 

 however, was busying himself about ethical matters, neglecting 



