Among the topics this paper will discuss, the leading one is that of the moral psychology of the Laws; it will not, however, attempt a general study of this, but will confine itself to the question whether that work presupposes any particular division of the soul into parts. The problem seems to have been on the whole neglected by scholars. Apelt in his Platon-Index says briefly that the soul is there treated as tripartite, which is certainly not true without qualification. Neither England's commentary nor Ritter's affords much help. The latter does, indeed, touch on the question in Volume II of his Platon; he there states that the Laws treats the soul as tripartite, and supports this by referring to I. 644C and IX. 863B, but neither passage proves his point, the second actually suggesting that it requires some modification, as will be argued below. The best treatment known to me is the discussion of the second of these passages by L. Gernet in his translation (with commentary) of Book IX, but it requires some expansion and supplementation.
It will be well to begin by recapitulating briefly the main points in the moral psychology of the Republic. The soul is there divided into three parts or (better) elements, the rational, the spirited and the appetitive, and this division has two aspects: (a) an analysis is thus provided which can be used in the interpretation and appraisal of all action whatever, the soul being in the right state and the agent's actions right in consequence when the rational element controls the appetitive through the agency of the spirited; (b) at the same time each of the three elements represents a drive towards one of three goals, the rational towards knowledge, the spirited towards honour and public distinction, and the appetitive towards pleasure (interpreted as bodily pleasure), or towards material gain as a means to the attainment of pleasure. Secondly, each of these three drives may predominate in any individual soul (though it is commonest for the last to do so, and least common for the first), and the three are therefore to be correlated with three ways of life, that of the thinker, that of the soldier or man in public life, and that of the merchant or other person engaged in a money-making enterprise, and further these ways of life are specially characteristic of different races. Thirdly, the three elements in the soul and the three types of character are correlated by Plato with the three classes in his ideal state, the rulers, the auxiliaries and the artisans. Fourthly, the distinction of three elements in the soul is made the basis for interpreting the four virtues, wisdom being the virtue of the rational element and courage of the spirited (ideally under the control of the rational), while justice consists in the maintenance of the proper relation between the three elements, the rational controlling the appetitive through the agency of the spirited, and temperance in the willing acquiescence of the appetites in the rule of reason. On the larger canvas of state organisation, the three classes will have as their specially characteristic virtues wisdom, courage and temperance respectively, while the state as a whole will be just if the correct relation between the three classes is maintained and the reason of the rulers preserves its control with the help of the auxiliaries. Fifthly, the tripartition of the soul is applied in Book IX to the discussion of pleasure, pleasures being graded as higher or lower according to the element in the soul which enjoys them; indeed, Plato argues that the pleasures of the rational element are not simply superior to those of the other two but more real as well.Finally, Book X suggests at least that the rational element is the real self, that it alone is immortal, and that the other two exist merely in virtue of our temporary attachment to a body.