Considered logically this concept is not identical with the totality of sense impressions referred to; but it is an arbitrary creation of the human (or animal) mind.
The scientist finds his reward in what Henri Poincare calls the joy of comprehension, and not in the possibility of application to which any discovery may lead.
What distinguishes the language of science from language as we ordinarily understand the word? ... What science strives for is an utmost acuteness and clarity of concepts as regards their mutual relation and their correspondence to sensory data.
Not until we dare to regard ourselves as a nation, not until we respect ourselves, can we gain the esteem of others, or rather only then will it come of its own accord
Concern for man and his fate must always form the chief interest of all technical endeavors. Never forget this in the midst of your diagrams and equations.
You are the only person I know who has the same attitude towards physics as I have: belief in the comprehension of reality through something basically simple and unified... It seems hard to sneak a look at God's cards. But that He plays dice and uses 'telepathic' methods... is something that I cannot believe for a single moment.