Just as courage imperils life, fear protects it.

Learning acquired in youth arrests the evil of old age.

Those who fall in love with practice without science are like a sailor who enters a ship without a helm or a compass, and who never can be certain whither he is going.

Therefore, O students, study mathematics and do not build without foundations.

Affective gestures pointing to things near either in time or space should be made with the hand not very far from the body of the person pointing; and if these things are distant, the hand of the painter should be more extended and the face turned toward the person to whom he is addressing the demonstration.

Those who, in debate, appeal to their qualifications, argue from memory, not from understanding.

Art lives from constraints and dies from freedom.