Who ever heard a theologian preface his creed, or a politician conclude his speech with an estimate of the probable error of his opinion?

[Regarding] the convention that clergymen are more virtuous than other men. Any average selection of mankind, set apart and told that it excels the rest in virtue, must tend to sink below the average.

Change is scientific; progress is ethical; change is indubitable, whereas progress is a matter of controversy.

Have no respect for the authority of others, for there are always contrary authorities to be found

When you want to teach children to think, you begin by treating them seriously when they are little, giving them responsibilities, talking to them candidly, providing privacy and solitude for them, and making them readers and thinkers of significant thoughts from the beginning. That’s if you want to teach them to think.

A man is rational in proportion as his intelligence informs and controls his desires.

Organic life, we are told, has developed gradually from the protozoon to the philosopher, and this development, we are assured, is indubitably an advance. Unfortunately it is the philosopher, not the protozoon, who gives us this assurance.