Ability in man is an apt ...

Ability in man is an apt good, if it be applied to good ends.
 Diogenes

Quotes from the same author

Wise kings generally have wise counselors; and he must be a wise man himself who is capable of distinguishing one.
 Diogenes
The mob is the mother of tyrants.
 Diogenes
A friend is one soul abiding in two bodies.
 Diogenes
The foundation of every state is the education of its youth.
 Diogenes
Those who have virtue always in their mouths, and neglect it in practice, are like a harp, which emits a sound pleasing to others, while itself is insensible of the music.
 Diogenes