Fear is the main source of superstition, and one of the main sources of cruelty. To conquer fear is the beginning of wisdom.

I can only say that, while my own opinions as to ethics do not satisfy me, other people's satisfy me still less.

Aristotle and Plato considered Greeks so innately superior to barbarians that slavery is justified so long as the master is Greek and the slave barbarian.

The morality of work is the morality of slaves, and the modern world has no need of slavery.

Change is one thing, progress is another.

These illustrations suggest four general maxims[...]. The first is: remember that your motives are not always as altruistic as they seem to yourself. The second is: don't over-estimate your own merits. The third is: don't expect others to take as much interest in you as you do yourself. And the fourth is: don't imagine that most people give enough thought to you to have any special desire to persecute you.

Although this may seem a paradox, all exact science is dominated by the idea of approximation. When a man tells you that he knows the exact truth about anything, you are safe in inferring that he is an inexact man. Every careful measurement in science is always given with the probable error ... every observer admits that he is likely wrong, and knows about how much wrong he is likely to be.