As Cicero continually refers to the views of earlier philosophers, it seems desirable here to give a short preliminary sketch, which may serve to show their relations to each other, leaving points of detail to be discussed in the notes on each particular passage.Greek philosophy had its origin not in the mother country, but in the colonies of Asia Minor and Magna Graecia. This is owing partly to the reflectiveness belonging to a more advanced civilization, and partly to the fact that the colonists were brought in contact with the customs and ideas of foreign nations. The philosophers of the earliest, or Pre-Socratic period, are broadly divided into the Ionic and the Italic Schools. Both had the same objects of interest, to ascertain the nature, the origin, the laws, the destiny of the visible world.

This book consists in a reprint of papers dealing mostly with Grecoroman philosophy, ranging from the 5th century BC to the 6th century AD, and concerned mainly with the Presocratics, Plato, Aristotle, the Early Academy, the Platonic and Aristotelian later traditions.