Only a few indications of history can be given here.
1. Earlier Views:
The conscience, at least the sequent conscience, was identified in the ancient world, and the rise of a doctrine on the subject belongs to the period when the human mind, being shut out from public activity through political changes, was thrown back upon itself and began to watch closely its own symptoms. The word has a specially prominent place in the philosophical writings of Cicero. Strange to say, it does not occur in the Old Testament; but, though not the name, the thing appears there frequently enough. On the very first page of revelation, the voice of God is heard calling among the trees of the garden (Ge 3:8); and, in the very next incident, the blood of Abel cries out to heaven from the ground (Ge 4:10). In the New Testament the word occurs with tolerable frequency, especially in the speeches (Ac 24:16, etc.) and writings of Paul (Ro 2:15; 9:1; 13:5; 1Co 6:7-12, etc.); and this might have been expected to secure for it a prominent place in the doctrine of the church. But this did not immediately take effect, although Chrysostom already speaks of Conscience and Nature as two books in which the human mind can read of God, previous to supernatural revelation. In the Middle Ages the conscience received from two sources so much stimulation that both thing and name were certain to come into greater prominence in the speculations of the schools. The one of these influences was the rise of Monasticism, which, driving human beings into solitude, made the movements of their own minds the objects of everlasting study to themselves; and the other was the practice of auricular confession, which became, especially to many of the inmates of the houses of religion, the most interesting business of life; because, in order to meet the confessor, they scanned every thought and weighed every scruple, becoming adepts at introspection and self-discipline. Thus it came to pass that ethics took the form of Cases of Conscience, the priest having to train himself, or to be trained by professors and through books, to be able to answer every query submitted to him in the confessional. The ripest fruit of this method appears in the Summa of Aquinas, who discusses elaborately the doctrine of conscience, dividing it into two parts--synderesis (from sunteresis) and conscientia--the one of which supplies the major premises and cannot err, while the other draws the inferences therefrom and is liable to make mistakes. The Mystics identified the synderesis as the point in the spirit of man at which it can be brought into contact and connection with the Spirit of God.
2. Reformation and After:
At the Reformation the conscience was much in the mouths of men, both because the terrors of conscience formed a preparation for comprehending justification by faith and because, in appearing before principalities and powers in vindication of their action, the Reformers took their stand on conscience, as Luther did so memorably at the Diet of Worms; and the assertion of the rights of conscience has ever since been a conspicuous testimony of Protestantism; whereas Romanists, especially as represented by the Jesuits, have treated the conscience as a feeble and ignorant thing, requiring to be led by authority--that is, by themselves. The forms of medievalism long clung even to Protestant literature on this subject. It may not be surprising to find a High Churchman like Jeremy Taylor, in his Ductor Dubitantium, discussing ethics as a system of cases of conscience, but it is curious to find a Puritan like Baxter (in his Christian Directory), and a Scottish Presbyterian like David Dickson (in his Therapeutica Sacra) doing the same. Deism in England and the Enlightenment in Germany magnified the conscience, to which they ascribed such a power of revealing God as made any further revelation unnecessary; but the practical effect was a secularization and vulgarization of the general mind; and it was against these rather than the system which had produced them that Butler in England and Kant in Germany had to raise the standard of a spiritual view of life. The former said of the conscience that, if it had power as it had right, it would absolutely govern the world; and Kant's sublime saying is well known, at the close of his great work on Ethics: "Two things fill the soul with ever new and growing wonder and reverence, the oftener and the longer reflection continues to occupy itself with them--the starry heavens above and the moral law within." The rise of an Associational and Developmental Philosophy in England, represented by such powerful thinkers as the Mills, father and son, Professor Bain and Herbert Spencer, tended to dissipate the halo surrounding the conscience, by representing it as merely an emotional equivalent for the authority of law and the claims of custom, so stamped on the mind by the experience of generations that, its earthly source forgotten, it came to be attributed to supernatural powers. But this school was antagonized with success by such thinkers as Martineau and T. H. Green. R. Rothe regarded conscience as a term too popular and of too variable signification to be of much use in philosophical speculation; but most of the great succession of writers on Christian ethics who followed him have treated it seriously; Dorner especially recognizing its importance, and Newman Smyth bestowing on it a thoroughly modern treatment. Among German works on the subject that of Gass, which contains an appendix on the history of the term synderesis, is deserving of special attention; that by Kahler is unfinished, as is also the work in English by Robertson; The Christian Conscience by Davison is slight and popular. Weighty discussions will be found in two books on Moral Philosophy--the Handbook of Calderwood, and the Ethics of Mezes. But there is abundance of room for a great monograph on the subject, which would treat conscience in a comprehensive manner as the subjective standard of conduct, formed by progressive familiarity with the objective standards as well as by practice in accordance with its own authority and with the will of God.
James Stalker