Toute passe–yesterday’s truth is to-day’s deception, and yesterday’s false inference may be to-morrow’s revelation.

Mistakes are, after all, the foundations of truth, and if a man does not know what a thing is, it is at least an increase in knowledge if he knows what it is not.

No one has yet discovered any warlike purpose to be served by the theory of numbers or relativity, and it seems very unlikely that anyone will do so for many years.

Je pravda denní a pravda noční. Pravda nemocných a pravda zdravých. Pravda dětí a pravda dospělých. Pravda mužů a pravda žen. Pravda živých a pravda umírajících. Pravda milujících a pravda nenávidících. Pravda šťastných a pravda nešťastných.

«It is impossible for the inhabitants of different worlds to walk or sit or stand on the same floor, because they have differing conceptions of what is horizontal and what is vertical. Yet they may well share the use of the same staircase. On the top staircase illustrated here, two people are moving side by side and in the same direction, and yet one of them is going downstairs and the other upstairs. Contact between them is out of the question because they live in different worlds and therefore can have no knowledge of each other's existence.»

Show me a sane man and I will cure him for you.