177. Under what conditions a person needs to be thus dealt with, what particular actions on his part constitute such an interference, is a question which can only be answered when we have considered what powers in particular need to be secured to individuals or to officials in order to the possibility of free action of the kind described. Every such power is a right of which the violation, if intended as a violation of a right, requires a punishment, of which the kind and amount must depend on the relative importance of the right and of the extent to which its general exercise is threatened. Thus every theory of rights in detail must be followed by, or indeed implies, a corresponding theory of punishment in detail, a theory which considers what particular acts are punishable, and how they should be punished. The latter cannot precede the former: all that can be done here is further to consider what general rules of punishment are implied in the principle on which we hold all right of punishment to rest, and how far in the actual practice of punishment that principle has been realised. 178. It is commonly asked whether punishment according to its proper nature is retributive or preventive or reformatory. The true answer is that it is and should be all three. The statement, however, that the punishment of the criminal by the state is retributive, though true in a sense that will be explained directly, yet so readily lends itself to a misunderstanding, that it is perhaps best avoided. It is not true in the sense that in legal punishment as it should be there survives any element of private vengeance, of the desire on the part of the individual who has received a hurt from another to inflict an equivalent hurt in return. It is true that the beginning of punishment by the state first appears in the form of a regulation of private vengeance, but it is not therefore to be supposed that punishment by the state is in any way a continuation of private vengeance. It is the essence of the former to suppress and supersede the latter, but it only does so gradually, just as rights in actuality are only formed gradually. Private vengeance belongs to the state of things in which rights are not as yet actualised; in the sense that the powers which it is for the social good that a man should be allowed to exercise, are not yet secured to him by society. In proportion as they are actualised, the exercise of private vengeance must cease. A _right_ of private vengeance is an impossibility; for, just so far as the vengeance is private, the individual in executing it is exercising a power not derived from society nor regulated by reference to social good, and such a power is not a right. Hence the view commonly taken by writers of the seventeenth and eighteenth centuries implies an entire misconception of the nature of a right; the view, viz., that there first existed rights of self-defence and self-vindication on the part of