He who, really sees all visible things, is said to have eyes and understanding. The faculty of understanding is known as such, because of the knowledge and comprehension it gives of unknown and incomprehensible things.
दृश्यं पश्यति यः पश्यन् स चक्षुष्मान् स बुद्धिमान्। अज्ञातानां च विज्ञानात् सम्बोधाद् बुद्धिरुच्यते।।२शा