Ignorance more frequently begets confidence than does knowledge: it is those who know little, and not those who know much, who so positively assert that this or that problem will never be solved by science.

It is no valid objection that science as yet throws no light on the far higher problem of the essence or origin of life. Who can explain the what is the essence of the attraction of gravity?

Science is always simple and always profound. It is only the half-truths that are dangerous.

Science is the captain, and practice the soldiers.

There is no royal road to science, and only those who do not dread the fatiguing climb of its steep paths have a chance of gaining its luminous summits.

Natural science will in time incorporate into itself the science of man, just as the science of man will incorporate into itself natural science: there will be one science.