Thus, in general terms, we may describe conscience. Coming now more closely to a philosophical analysis of the conception, we shall find therein much enlightenment for the purposes of our present investigation. In the first place, the word is of comparatively late origin. It does not occur in the Hebrew writers of the Old Testament. Its earliest appearance is in the Book of Wisdom, the work of a Hellenistic Jew extremely well acquainted with the trend of Greek thought in the third century B.C. It does not occur in the Gospels, except in the story of the sinful woman whom Christ refused to condemn--a history which, though profoundly in accord with the sympathetic genius of Jesus, is none the less an interpolation in the eighth chapter of the Johannine Gospel, so much so that Tischendorff excised it from his last edition of the text of the New Testament. St. Paul certainly uses the word once in the Epistle to the Romans, and though known in the latter days before the advent of Christianity, we may assume that mainly through that religion the word was popularised throughout the world.
But what is the faculty which corresponds to the word conscience? We shall find etymology of great assistance in giving precision to our thoughts. The word is, of course, a derivative from the Latin, _conscientia_, knowledge with, or together. Now, _scientia_ is the simple knowledge of things by the reason, while _conscientia_ is the knowledge which the reason has of itself; it is the realisation of one's selfhood--the realisation of the _ichkeit des ego_, as the very expressive German phrase has it, "the selfhood of the I". In English philosophical language we commonly denominate this self-realisation consciousness, a word of precisely the same etymological origin as conscience. If, in the next place, the reason is occupied, not with the reflex action of self-contemplation, but with moral action or the discernment of right from wrong, then it is called, and is, no longer consciousness, but _conscience_. Putting it technically, consciousness is a psychological expression, while conscience is ethical.
Nevertheless, it must be most carefully remembered that the two functions are performed by one and the same reason--immaterial and indivisible in us. Truly speaking, there is no real, but only a conceptual, distinction between the reason of a Darwin elaborating his famous law, realising his selfhood, and acknowledging his obligations to the eminent man--only less so than himself--who had simultaneously lighted on the great discovery of the age--the law of organic evolution. As Paul says of those manifold endowments of the earliest Christians, "A diversity of gifts and a diversity of graces, but in them all worketh the self-same spirit," so say we of the reason at the very heart of our being, the sole, self-sufficing explanation of the multitudinous phenomena of our mental life. Hence we arrive at a definition of conscience as "the practical dictate of the reason in us prescribing obedience to the good and avoidance of the evil". Two elements, therefore, are discernible in this definition: first, reason, as such, pointing out what is good and evil; and, secondly, reason, as conscience, ordaining that the good is to be done and the evil left undone--a distinction to be carefully borne in mind when the problem of conflicting consciences has to be faced; how it comes, for instance, that morality appears to differ in different countries, and even in the same individual at different periods of his life.