Necessity is a guardian in Nature.

To me it seems that those sciences are vain and full of error which are not born of experience, mother of all certainty, first-hand experience which in its origins, or means, or end has passed through one of the five senses.

Medicine is the restoration of discordant elements; sickness is the discord of the elements infused into the living body.

Necessity is the mistress and guide of nature.

Patience serves as a protection against wrongs as clothes do against cold.

To speak of this subject you must... explain the nature of the resistance of the air, in the second the anatomy of the bird and its wings, in the third the method of working the wings in their various movements, in the fourth the power of the wings and the tail when the wings are not being moved and when the wind is favourable to serve as guide in various movements.

Tears come from the heart and not from the brain