The eye, form, and light, form the three requisites of the action called Seeing. The same holds good about the action of the other senses and the ideas which is their result.
रूपं चक्षुः प्रकाशश्च दर्शने हेतवस्त्रयः। यथैवात्र तथान्येषु ज्ञानज्ञेयेषु हेतवः॥