Scientific principles and laws do not lie on the surface of nature. They are hidden, and must be wrested from nature by an active and elaborate technique of inquiry.

Human nature exists and operates in an environment. And it is not 'in' that environment as coins are in a box, but as a plant is in the sunlight and soil.

Since changes are going on anyway, the great thing is to learn enough about them so that we will be able to lay hold of them and turn them in the direction of our desires. Conditions and events are neither to be fled from nor passively acquiesced in; they are to be utilized and directed.

If a person cannot foresee the consequences of his act, and is not capable of understanding what he is told about its outcome by those with more experience, it is impossible for him to guide his act intelligently. In such a state, every act is alike to him.

Liberty is not just an idea, an abstract principle. It is power, effective power to do specific things. There is no such thing as liberty in general; liberty, so to speak, at large.

We have three approaches at our disposal: the observation of nature, reflection, and experimentation. Observation serves to assemble the data, reflection to synthesise them and experimentation to test the results of the synthesis. The observation of nature must be assiduous, just as reflection must be profound, and experimentation accurate. These three approaches are rarely found together, which explains why creative geniuses are so rare.

We can have facts without thinking but we cannot have thinking without facts.