The essay consists in the analysis of the problem of the evil in the man and in the analysis of the remedies which the man can find against the evil. Plato affirms the presence of an active principle of evil in the soul of every man, which coincides with some instincts of the appetitive soul; the opposite principle to the evil is the reason, which needs, though, a correct education in order to be able to fight efficiently against the evil in us. The man can be seen as a battle field of these opposite forces. Plato describes the presence of the evil in us in some passages of Republic Book 9, where he compares the appetitive part of the soul with a monster. The destiny of every person in her earthly existence consists in the continuing control of the appetitive part of the soul, if the status of ethical education is to be reached and maintained. The man who remains in the realm of the opinion, that is, in the realm of the doxa is an individual who only disposes of unstable opinions and who as a consequence do not have authentic remedies against the appetitive part. On the contrary, the individual who can ascend to the realm of being through the hard education represented by arithmetic, geometry, stereometry, astronomy, harmony and, finally, dialectic is really able to contrast the force of the evil within the individual. Ethics is really possible only through the complete education which passes through these disciplines: the more the individuals is theoretically educated, the more the individual is ethically educated. The knowledge of ideas is the only authentic therapy against the evil in us.