The existing scientific concepts cover always only a very limited part of reality, and the other part that has not yet been understood is infinite.

Whether we electrons, light quanta, benzol molecules, or stones, we shall always come up against these two characteristics, the corpuscular and the undular.

Nature is made in such a way as to be able to be understood. Or perhaps I should put it-more correctly-the other way around, and say that we are made in such a way as to be able to understand Nature.

The solution of the difficulty is that the two mental pictures which experiment lead us to form - the one of the particles, the other of the waves - are both incomplete and have only the validity of analogies which are accurate only in limiting cases.

We will have to abandon the philosophy of Democritus and the concept of elementary particles. We should accept instead the concept of elementary symmetries.

It seems sensible to discard all hope of observing hitherto unobservable quantities, such as the position and period of the electron... Instead it seems more reasonable to try to establish a theoretical quantum mechanics, analogous to classical mechanics, but in which only relations between observable quantities occur.

The violent reaction on the recent development of modern physics can only be understood when one realises that here the foundations of physics have started moving; and that this motion has caused the feeling that the ground would be cut from science