Nietzsche would define man as an animal that can make and keep promises.
He sees the real nobility of man in his capacity for promising something, answering for himself and undertaking a responsibility--since man, with the mastery of himself which this capacity implies, necessarily acquires in addition a mastery over external circumstances and over other creatures, whose will is not so lasting.
The consciousness of this responsibility is what the sovereign man calls his conscience.
What, then, is the past history of this responsibility, this conscience? It is a long and bloody one. Frightful means have been used in the course of history to train men to remember what they have once promised or willed, tacitly or explicitly. For milleniums man was confined in the strait-jacket of the morality of custom, and by such punishments as stoning, breaking on the wheel or burning, by burying the sinner alive, tearing him asunder with horses, throwing him into the water with a stone on his neck or in a sack, by scourging, flaying and branding--by all these means a long memory for what he had promised was burnt into that forgetful animal, man; in return for which he was permitted to enjoy the advantages of being a member of society.
According to Nietzsche's hypothesis, the consciousness of guilt originates simply as consciousness of a debt. The relation of contract between creditor and debtor, which is as old as the earliest primitive forms of human intercourse in buying, selling, bartering, etc.--this is the relation that underlies it. The debtor (in order to inspire confidence in his promise of repayment) pledges something he possesses: his liberty, his woman, his life; or he gives his creditor the right of cutting a larger or smaller piece of flesh from his body, according to the amount of the debt. (The Roman Code of the Twelve Tables; again in The Merchant of Venice.)
The logic of this, which has become somewhat strange to us, is as follows: as compensation for his loss the creditor is granted a kind of voluptuous sensation, the delight of being able to exercise his power upon the powerless.
The reader may find evidence in Rée (op. cit., p. 13 ff.) for Nietzsche's dictum, that for milleniums this was the view of mankind: The sight of suffering does one good.
The infliction of suffering on another is a feast at which the fortunate one swells with the joy of power. We may also find evidence in Rée that the instincts of pity, fairness and clemency, which were afterwards glorified as virtues, were originally regarded almost everywhere as morally worthless, nay, as indications of weakness.
Buying and selling, as well as everything psychologically connected therewith and older than any form of social organisation, contain the germs, in Nietzsche's view, of compensation, assessing, justice and duty. Man soon became proud of himself as a being who measures values. One of the earliest generalisations was this: Everything has its price. And the thought that everything can be paid for was the oldest and most naïve canon of justice.
Now the whole of society, as it gradually develops, stands in the same relation to its members as the creditor to the debtor. Society protects its members; they are assured against the state of outlawry--on condition that they do not break their pledges to the community. He who breaks his word--the criminal--is relegated to the outlawry involved in exclusion from society.