To the perpetual shame and abasement of the evil men of Italy who commend the Mother Tongue of other nations and depreciate their own, I say that their action proceeds from five abominable causes: the first is blindness of discretion; the second, mischievous self-justification; the third, greed of vainglory; the fourth, an invention of envy; the fifth and last, vileness of mind, that is, cowardice.

And each one of these grave faults has a great following, for few are those who are free from them.
Of the first, one can reason thus.

As the sensitive part of the soul has its eyes, with which it learns the difference of things, inasmuch as they are coloured externally; so the rational part has its eye with which it learns the difference of things, inasmuch as each is ordained to some end; and this is discretion.

And as he who is blind with the eyes of sense goes always according to the guidance of others judging evil and good; so he who is blinded from the light of discretion, always goes in his judgment according to the cry, right or wrong as it may be.

Hence, whenever the guide is blind, it must follow that what blind man soever leans on him must come to a bad end.