For many medieval thinkers, Plato's thinking provided the necessary philosophical groundwork for belief in an afterlife. For the most part, the medieval theologian/philosophers welded Platonism to Christianity so firmly that criticism of the synthesis was nearly tantamount to heresy. This dogmatism was reflected clearly in Bonaventure (1221–1274), a Franciscan and Augustinian thinker who rejected the influx of Aristotelian ideas in his time because they seemed to deny the immortality of the soul.
Attributing any particular instance of this sort of error to either a cognitive or ethical shortcoming is difficult. Plato doesn’t depict Meno as an incorrigible snob; he actually behaves much better than another character in the dialogue, Anytus, who becomes enraged with Socrates and threatens him. But imagine a spectrum of susceptibility to fancy yet vapid language. While intelligence might provide some protection against the seductions of such words, a lack of pretentiousness would also be an asset. Like overconfidence, pretentiousness has a moral valence. Avoiding it is not only a matter of debugging some glitch in our mental software, it’s a moral achievement.
Socrates then proceeds to find the corresponding four virtues in the individual (434d). Socrates defends the analogy of the city and the individual (435a-b) and proceeds to distinguish three analogous parts in the soul with their natural functions (436b). By using instances of psychological conflict, he distinguishes the function of the rational part from that of the appetitive part of the soul (439a). Then he distinguishes the function of the spirited part from the functions of the two other parts (439e-440e). The function of the rational part is thinking, that of the spirited part the experience of emotions, and that of the appetitive part the pursuit of bodily desires. Socrates explains the virtues of the individual’s soul and how they correspond to the virtues of the city (441c-442d). Socrates points out that one is just when each of the three parts of the soul performs its function (442d). Justice is a natural balance of the soul’s parts and injustice is an imbalance of the parts of the soul (444e). Socrates is now ready to answer the question of whether justice is more profitable than injustice that goes unpunished (444e-445a). To do so he will need to examine the various unjust political regimes and the corresponding unjust individuals in each (445c-e).