Extinguished theologians lie about the cradle of every science, as strangled snakes beside that of Hercules

Only one absolute certainty is possible to man, namely that at any given moment the feeling which he has exists.

Not only do I disbelieve in the need for compensation, but I believe that the seeking for rewards and punishments out of this lifeleads men to a ruinous ignorance of the fact that their inevitable rewards and punishments are here.

There is but one right, and the possibilities of wrong are infinite.

The struggle for existence holds as much in the intellectual as in the physical world. A theory is a species of thinking, and its right to exist is coextensive with its power of resisting extinction by its rivals.

I have endeavoured to show that no absolute structural line of demarcation, wider than that between the animals which immediately succeed us in the scale, can be drawn between the animal world and ourselves; and I may add the expression of my belief that the attempt to draw a physical distinction is equally futile, and that even the highest faculties of feeling and of intellect begin to germinate in lower forms of life.

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