“Man can learn nothing unless he proceeds from the known to the unknown.”

When entering on new ground we must not be afraid to express even risky ideas so as to stimulate research in all directions. As Priestley put it, we must not remain inactive through false modesty based on fear of being mistaken.

Theories are like a stairway; by climbing, science widens its horizon more and more, because theories embody and necessarily include proportionately more facts as they advance.

The first requirement in using statistics is that the facts treated shall be reduced to comparable units.

We achieve more than we know. We know more than we understand. We understand more than we can explain.

The stability of the internal medium is a primary condition for the freedom and independence of certain living bodies in relation to the environment surrounding them.

We must never make experiments to confirm our ideas, but simply to control them.

We must keep our freedom of mind, and must believe that in nature what is absurd, according to our theories, is not always impossible.

The goal of scientific physicians in their own science … is to reduce the indeterminate. Statistics therefore apply only to cases in which the cause of the facts observed is still indeterminate.

Science admits no exceptions; otherwise there would be no determinism in science, or rather, there would be no science.

Mediocre men often have the most acquired knowledge. It is in the darker. It is in the darker regions of science that great men are recognized; they are marked by ideas which light up phenomena hitherto obscure and carry science forward.

Experiment is fundamentally only induced observation.

The science of life is a superb and dazzlingly lighted hall which may be reached only by passing through a long and ghastly kitchen.

Our ideas are only intellectual instruments which we use to break into phenomena; we must change them when they have served their purpose, as we change a blunt lancet that we have used long enough.

Now, a living organism is nothing but a wonderful machine endowed with the most marvellous properties and set going by means of the most complex and delicate mechanism.

The eloquence of a scientist is clarity; scientific truth is always more luminous when its beauty is unadorned than when it is tricked out in the embellishments with which our imagination would seek to clothe it.

In science, the best precept is to alter and exchange our ideas as fast as science moves ahead.

[H]istory is seen in a rear-view mirror while the future is the dark, foggy road ahead, filled with unknown trouble.

Now, however, an attack may come without warning from an unknown enemy, to achieve unclear motives.

It’s actually quite a good ethos for life: go into the unknown with truth, commitment, and openness and mostly you’ll be okay.

It is not unknown for fathers with a brace of daughters to reel off their names in order of birth when summoning the youngest.

A new day is here. Yesterday is a memory. Tomorrow is unknown. Now is the knowing.

I would rather like to think of God as being a kind of adventurer – even as Wells thought about him – or perhaps as something within us making for some unknown purpose.

Take one step backward into the unknown.

If you have to ask, you’ll never know.