“No, our science is no illusion. But an illusion it would be to suppose that what science cannot give us we can get elsewhere.”

“We believe that it is possible for scientific work to gain some knowledge about the reality of the world, by means of which we can increase out power and in accordance with which we can arrange our life. If this belief is an illusion, then we are in the same position as you. But science has given us evidence by its numerous and important successes that it is no illusion.”

“Observe the difference between your attitude to illusions and mine. You have to defend the religious illusion with all your might. If it becomes discredited - and indeed the threat to it is great enough - then your world collapses. There is nothing left for you but to despair of everything, of civilization and the future of mankind. From that bondage I am, we are, free. Since we are prepared to renounce a good part of our infantile wishes, we can bear it if a few of our expectations turn out to be illusions.”

“Religion is an illusion and it derives its strength from the fact that it falls in with our instinctual desires.”

“Poets are masters of us ordinary men, in knowledge of the mind,because they drink at streams which we have not yet made accessible to science.”

“Illusions commend themselves to us because they save us pain and allow us to enjoy pleasure instead. We must therefore accept it without complaint when they sometimes collide with a bit of reality against which they are dashed to pieces.”

“Religious doctrines … are all illusions, they do not admit of proof, and no one can be compelled to consider them as true or to believe in them.”