Know the atman to be the master of the chariot; the body, the chariot; the buddhi, the charioteer; and the mind, the reins.
The senses, they say, are the horses; the objects, the roads. The wise call the atman —united with the body, the senses, and the mind — the enjoyer.
If the buddhi [intellect], being related to a mind that is always distracted, loses its discrimination, then the senses become uncontrolled, like the vicious horses of a charioteer.
But if the buddhi, being related to a mind that is always restrained, possesses discrimination, then the senses come under control, like the good horses of a charioteer.