A subtle thought that is in error may yet give rise to fruitful inquiry that can establish truths of great value.

Now any dogma, based primarily on faith and emotionalism, is a dangerous weapon to use on others, since it is almost impossible to guarantee that the weapon will never be turned on the user.

There is no belief, however foolish, that will not gather its faithful adherents who will defend it to the death.

During the century after Newton, it was still possible for a man of unusual attainments to master all fields of scientific knowledge. But by 1800, this had become entirely impracticable.

I made up my mind long ago to follow one cardinal rule in all my writing — to be clear.

Having no unusual coincidence is far more unusual than any coincidence could possibly be.

Life would be impossible on such a planet. It wouldn't get enough heat and light, and if it rotated there would be total darkness half of every day. There wouldn't be any native inhabitants. You couldn't expect life - which is fundamentally dependent on light - to develop under such extreme conditions of light deprivation. Half of every axial rotation spent in Darkness! No, nothing could exist under conditions like that.