Medicine is the science by which we learn the various states of the human body in health and when not in health, and the means by which health is likely to be lost and when lost is likely to be restored.

The world is divided into men who have wit and no religion and men who have religion and no wit.

An experiment is a question which science poses to Nature, and a measurement is the recording of Nature's answer.

-- Max Planck

I frame no hypotheses.

-- Isaac Newton

The seeker after truth is not one who studies the writings of the ancients and, following his natural disposition, puts his trust in them, but rather the one who suspects his faith in them and questions what he gathers from them.

-- Ibn al-Haytham

Measure what is measurable, and make measurable what is not so.

-- Galileo Galilei

To know that we know what we know, and to know that we do not know what we do not know, that is true knowledge.

-- Nicolaus Copernicus

The first principle is that you must not fool yourself -- and you are the easiest person to fool.

-- Richard Feynman