Agnosticism simply means that a man shall not say that he knows or believes that for which he has no grounds for professing to believe.

If the twentieth century is to be better than the nineteenth, it will be because there are among us men who walk in Priestley's footsteps....To all eternity, the sum of truth and right will have been increased by their means; to all eternity, falsehoods and injustice will be the weaker because they have lived.

The doctrine that all men are, in any sense, or have been, at any time, free and equal, is an utterly baseless fiction.

Science reckons many prophets, but there is not even a promise of a Messiah.

To a person uninstructed in natural history, his country or sea-side stroll is a walk through a gallery filled with wonderful works of art, nine-tenths of which have their faces turned to the wall. Teach him something of natural history, and you place in his hands a catalogue of those which are worth turning around. Surely our innocent pleasures are not so abundant in this life, that we can afford to despise this or any other source of them.

The ultimate court of appeal is observation and experiment... not authority.

Irrationally held truths may be more harmful than reasoned errors.