Niels Bohr

The word 'reality' is also a word, a word which we must learn to use correctly.

Accuracy and clarity of expression are a matter of degree.

We must be clear that, when it comes to atoms, language can be used only as in poetry. The poet, too, is not nearly so concerned with describing facts as with creating images and establishing mental connections.

One must make a distinction between the two types of truth, the trivial ones where opposites are clearly absurd, and the profound truths, where the opposite is also a profound truth.

Light and justice are not goods, but they are the condition of goods.

The meaning of life does not consist in the mere fact of existing, but in the power of perceiving and making known our existence, and that of others.

The aim of science is to purify our notions, not to increase the number of facts.

The meaning of 'real' is not a fixed one, but depends on the context.

Every great and deep difficulty bears in itself its own solution. It forces us to change our thinking in order to find it.

If we would understand the atom, we must be able to describe it in its totality, and not merely in its parts.

The purpose of science is not to answer ultimate questions, but to make progress in understanding.

The electron is an elementary particle, but it is not a 'thing' in the usual sense of the word.

The goal of science is to explain the world, not to describe it.

The atom is not a mechanical system, but a system of relationships.

The problem is not to know what the world is, but what we can say about it.

The fundamental problem of all science is the description of the world.

If quantum mechanics hasn't profoundly shocked you, you haven't understood it yet.

Your theory is crazy, but it's not crazy enough to be true.

We are all agreed that your theory is crazy. The question which divides us is whether it is crazy enough to have a chance of being correct.

Every sentence I utter must be understood not as an affirmation, but as a question.