At this point we must say something of the efficient cause of the princely part. This will be to show by demonstration who has the authority to elect it, and consequently to establish the other parts of the city. For enough has been said concerning the institution of a non-elected princely part in chapter 11 of this discourse, section 5. Let us begin, however, by first deciding what kind of a man it is appropriate to elect or promote to the office of prince; for this will give us a surer transition to the authority that effects his election or institution.
Now the inner dispositions of the perfect future prince are two in number, though they are not essentially separate: viz. prudence and moral virtue, especially justice. The one, sc. prudence, is to direct his intelligence in exercising his office; hence Politics III, chapter 2: ‘Prudence alone is the virtue peculiar to the prince; it seems appropriate that the others are common to subjects and princes.’ The other disposition is that by which his sentiments are upright, sc. moral virtue, and of these most especially justice. Hence Aristotle says, Ethics IV, in the treatise on justice: ‘The prince is the guardian of the just.’
Prudence, then, is necessary to the future prince, because it gives him a great capacity for his proper work, viz. the judgement of what is advantageous and just in civil terms. For in those human civil actions where either the action itself, or its manner, is not decided by law, it is prudence that guides the prince both in judging and in executing, the deed or its manner or both: where without prudence he would make a mistake. For (as in Sallust's Catiline) if Cicero as consul had punished Catiline's accomplices – powerful Roman citizens who had conspired against the republic, and were therefore liable to the death penalty – according to the law and in the habitual time, place and manner, it is likely that civil war would have arisen as a result; and this would have caused the polity to disintegrate because of the sedition stirred up among the people by the said conspirators against the consul and others in the position of prince.