[160] Therefore knowledge causes hearing and seeing, by means of which faculties success and rectitude of conduct are arrived at; for he who sees and hears, knowing what is expedient, chooses that, and rejecting the contrary is benefited by his knowledge. But ignorance causes to the soul a mutilation more grievous than the mutilation of the body, and is the cause of many errors, since it is unable to derive any assistance from without, either by foreseeing anything, or by any acuteness of hearing. Therefore, owing to its exceeding desolateness of condition, it is left utterly undefended and unprotected, and is exposed to the plots of all kinds of men and to dangers from all kinds of events.