A professor is one who can speak on any subject -- for precisely fifty minutes.
The modern physicist is a quantum theorist on Monday, Wednesday, and Friday and a student of gravitational relativity theory on Tuesday, Thursday, and Saturday. On Sunday he is neither, but is praying to his God that someone, preferably himself, will find the reconciliation between the two views.
Progress imposes not only new possibilities for the future but new restrictions.
The Advantage is that mathematics is a field in which one's blunders tend to show very clearly and can be corrected or erased with a stroke of the pencil. It is a field which has often been compared with chess, but differs from the latter in that it is only one's best moments that count and not one's worst. A single inattention may lose a chess game, whereas a single successful approach to a problem, among many which have been relegated to the wastebasket, will make a mathematician's reputation.
[with A Rosenblueth]
The best material model of a cat is another, or preferably the same, cat.
Scientific discovery consists in the interpretation for our own convenience of a system of existence which has been made with no eye to our convenience at all.
One of the chief duties of a mathematician in acting as an advisor to scientists is to discourage them from expecting too much of mathematicians.
We mathematicians who operate with nothing more expensive than paper and possibly printers' ink are quite reconciled to the fact that, if we are working in an active field, our discoveries will commence to be obsolete at the moment that they are written down or even at the moment they are conceived. We know that for a long time everything we do will be nothing more than the jumping off point for those who have the advantage of already being aware of our ultimate results. This is the meaning of the famous apothegm of Newton, when he said, "If I have seen further than other men, it is because I have stood on the shoulders of giants".
Mathematics is too arduous and uninviting a field to appeal to those to whom it does not give great rewards. These rewards are of exactly the same character as those of the artist. To see a difficult uncompromising material take living shape and meaning is to be Pygmalion, whether the material is stone or hard, stonelike logic. To see meaning and understanding come where there has been no meaning and no understanding is to share the work of a demiurge. No amount of technical correctness and no amount of labour can replace this creative moment, whether in the life of a mathematician or of a painter or musician. Bound up with it is a judgement of values, quite parallel to the judgement of values that belongs to the painter or the musician. Neither the artist nor the mathematician may be able to tell you what constitutes the difference between a significant piece of work and an inflated trifle; but if he is not able to recognise this in his own heart, he is no artist and no mathematician.
What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.