Procreation is nature's principal occupation, and every man, whether he be young or old, when meeting every woman measures the potentiality of sex between them.

Necessity is the theme and the inventress, the eternal curb and law of nature.

Nature is the source of all true knowledge. She has her own logic, her own laws, she has no effect without cause nor invention without necessity.

Necessity is the mistress and guide of nature.

Human subtlety will never devise an invention more beautiful, more simple or more direct than does nature because in her inventions nothing is lacking, and nothing is superfluous.

Although nature commences with reason and ends in experience it is necessary for us to do the opposite, that is to commence with experience and from this to proceed to investigate the reason.