Letter 94 (§13)

““There are two reasons why we go astray: either there is in the soul an evil quality which has been brought about by wrong opinions, or, even if not possessed by false ideas, the soul is prone to falsehood and rapidly corrupted by some outward appearance which attracts it in the wrong direction. For this reason it is our duty either to treat carefully the diseased mind and free it from faults, or to take possession of the mind when it is still unoccupied and yet inclined to what is evil. Both these results can be attained by the main doctrines of philosophy; therefore the giving of such precepts is of no use.”