Classicly

The reason passes, like the heart, through certain epochs and transitions, but its development is not so often portrayed. Men seem to have been satisfied with unfolding the passions in their extremes, their aberration, and their results, without considering how closely they are bound up with the intellectual constitution of the individual.

Degeneracy in morals roots in a one-sided and wavering philosophy, doubly dangerous, because it blinds the beclouded intellect with an appearance of correctness, truth, and conviction, which places it less under the restraining influence of man's instinctive moral sense. On the other hand, an enlightened understanding ennobles the feelings,—the heart must be formed by the head.