THE meaning of the term Gnosis or Knowledge, as applied to a system of philosophy, may be illustrated by the language of Plato towards the end of the fifth book of the Republic, in which he distinguishes between knowledge and opinion as being concerned respectively with the real and the apparent. When to this distinction is added the further explanation that the objects of sense; the visible things of the world, belong to the class of phenomena and are objects of opinion, while the invisible essence of things, the one as distinguished from the many, is the true reality, discerned not by sense but by intellect, we shall be justified in identifying knowledge with that a apprehension of things which penetrates beyond their sensible appearances to their essence and cause, and which differs in name only from that wisdom which Aristotle tells us is by common consent admitted to consist in a knowledge of first Causes or Principles. In this general sense however, the term gnosis has nothing to distinguish it from the ordinary Greek conception of philosophy , and so long as it remains solely within the region of philosophical inquiry and terminology, we do not find it generally employed to designate either philosophy as a whole or any special philosophical system. It is not till after the Christian era that the term comes into use as the distinct designation of a certain form of religious philosophy, emanating in some degree from Christian sources, and influenced by Christian ideas and Christian language. Even in the earlier association of Greek philosophy with a revealed religion, which is manifested in the GraecoJewish philosophy of Alexandria, though the teaching of Philo may be regarded as embodying the essential constituents of Gnosticism in an entire if an undeveloped form, we do not find the distinctive name of Gnosis or Gnostic applied to designate the system or its teachers.