Priestley [said] that each discovery we make shows us many others that should be made.

Science does not permit exceptions.

But while I accept specialization in the practice, I reject it utterly in the theory of science.

Proof that a given condition always precedes or accompanies a phenomenon does not warrant concluding with certainty that a given condition is the immediate cause of that phenomenon. It must still be established that when this condition is removed, the phenomen will no longer appear.

[Those] who have an excessive faith in their theories or in their ideas are not only poorly disposed to make discoveries, but they also make very poor observations.

The experimenter who does not know what he is looking for will not understand what he finds.

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.