Therefore in medicine we ought to know the causes of sickness and health.

Now it is established in the sciences that no knowledge is acquired save through the study of its causes and beginnings, if it has had causes and beginnings; nor completed except by knowledge of its accidents and accompanying essentials.

As to the mental essence, we find it in infants devoid of every mental form.

An ignorant doctor is the aide-de-camp of death.

It is in the nature of water ... to become transformed into earth through a predominating earthy virtue; ... it is in the nature of earth to become transformed into water through a predominating aqueous virtue.