“I believe that liberty is the only genuinely valuable thing that men have invented, at least in the field of government, in a thousand years. I believe that it is better to be free than to be not free, even when the former is dangerous and the latter safe. I believe that the finest qualities of man can flourish only in free air – that progress made under the shadow of the policeman’s club is false progress, and of no permanent value. I believe that any man who takes the liberty of another into his keeping is bound to become a tyrant, and that any man who yields up his liberty, in however slight the measure, is bound to become a slave.”

"What I Believe" in The Forum 84 (September 1930), p. 139; some of these expressions were also used separately in other Mencken essays.
1930s
Context: I believe that religion, generally speaking, has been a curse to mankind — that its modest and greatly overestimated services on the ethical side have been more than overcome by the damage it has done to clear and honest thinking.
I believe that no discovery of fact, however trivial, can be wholly useless to the race, and that no trumpeting of falsehood, however virtuous in intent, can be anything but vicious.
I believe that all government is evil, in that all government must necessarily make war upon liberty and the democratic form is as bad as any of the other forms.
I believe that the evidence for immortality is no better than the evidence of witches, and deserves no more respect.
I believe in the complete freedom of thought and speech — alike for the humblest man and the mightiest, and in the utmost freedom of conduct that is consistent with living in organized society.
I believe in the capacity of man to conquer his world, and to find out what it is made of, and how it is run.
I believe in the reality of progress.
I —But the whole thing, after all, may be put very simply. I believe that it is better to tell the truth than to lie. I believe that it is better to be free than to be a slave. And I believe that it is better to know than be ignorant.

"Why Liberty?”, in the Chicago Tribune (30 January 1927)
1920s
Context: I believe that liberty is the only genuinely valuable thing that men have invented, at least in the field of government, in a thousand years. I believe that it is better to be free than to be not free, even when the former is dangerous and the latter safe. I believe that the finest qualities of man can flourish only in free air – that progress made under the shadow of the policeman’s club is false progress, and of no permanent value. I believe that any man who takes the liberty of another into his keeping is bound to become a tyrant, and that any man who yields up his liberty, in however slight the measure, is bound to become a slave.

Legislative Assembly, February 9, 1865
Context: The two greatest things that all men aim at in any free government are liberty and permanency. We have had liberty enough - too much perhaps in some respects - but at all events, liberty to our hearts content.

Quoted in Einstein: His Life and Universe http://books.google.com/books?id=dJMpQagbz_gC&lpg=PP1&pg=PA387#v=onepage&q&f=false by Walter Isaacson, p. 387
1920s, Viereck interview (1929)

Religion and Philosophy in Germany, A fragment https://archive.org/stream/religionandphilo011616mbp#page/n5/mode/2up. p. 25
Context: I believe in progress; I believe that happiness is the goal of humanity, and I cherish a higher idea of the Divine Being than those pious folk who suppose that man was created only to suffer. Even here on earth I would strive, through the blessings of free political and industrial institutions, to bring about that reign of felicity which, in the opinion of the pious, is to be postponed till heaven is reached after the day of Judgment. The one expectation is perhaps as vain as the other; there may be no resurrection of humanity either in a political or in a religious sense. Mankind, it may be, is doomed to eternal misery; the nations are perhaps under a perpetual curse, condemned to be trodden under foot by despots, to be made the instruments of their accomplices and the laughing-stocks of their menials. Yet, though all this be the case, it will be the duty even of those who regard Christianity as an error still to uphold it; and men must journey barefoot through Europe, wearing monks' cowls, preaching the doctrine of renunciation and the vanity of all earthly possessions, holding up before the gaze of a scourged and despised humanity the consoling Cross, and promising, after death, all the glories of heaven.
The duration of religions has always been dependent on human need for them. Christianity has been a blessing for suffering humanity during eighteen centuries; it has been providential, divine, holy. All that it has done in the interest of civilisation, curbing the strong and strengthening the weak, binding together the nations through a common sympathy and a common tongue, and all else that its apologists have urged in its praise all this is as nothing compared with that great consolation it has bestowed on man. Eternal praise is due to the symbol of that suffering God, the Saviour with the crown of thorns, the crucified Christ, whose blood was as a healing balm that flowed into the wounds of humanity. The poet especially must acknowledge with reverence the terrible sublimity of this symbol.

Address to the court in People v. Lloyd (1920)

Notes for an oration at Braintree (Spring 1772)
1770s

Variant: And this I believe: that the free, exploring mind of the individual human is the most valuable thing in the world. And this I would fight for: the freedom of the mind to take any direction it wishes, undirected.
Source: East of Eden (1952)
Context: And this I believe: that the free, exploring mind of the individual human is the most valuable thing in the world. And this I would fight for: the freedom of the mind to take any direction it wishes, undirected. And this I must fight against: any religion, or government which limits or destroys the individual. This is what I am and what I am about.
Context: Our species is the only creative species, and it has only one creative instrument, the individual mind and spirit of a man. Nothing was ever created by two men. There are no good collaborations, whether in art, in music, in poetry, in mathematics, in philosophy. Once the miracle of creation has taken place, the group can build and extend it, but the group never invents anything. The preciousness lies in the lonely mind of a man.
And now the forces marshaled around the concept of the group have declared a war of extermination on that preciousness, the mind of man. By disparagement, by starvation, by repressions, forced direction, and the stunning blows of conditioning, the free, roving mind is being pursued, roped, blunted, drugged. It is a sad suicidal course our species seems to have taken.
And this I believe: that the free, exploring mind of the individual human is the most valuable thing in the world. And this I would fight for: the freedom of the mind to take any direction it wishes, undirected. And this I must fight against: any religion, or government which limits or destroys the individual. This is what I am and what I am about. I can understand why a system built on a pattern must try to destroy the free mind, for it is the one thing which can by inspection destroy such a system. Surely I can understand this, and I hate it and I will fight against it to preserve the one thing that separates us from the uncreative beasts. If the glory can be killed, we are lost.

Essay in This I Believe : 2 (1952) edited by Edward R. Murrow, p. 142
Context: What do I believe? As an American I believe in generosity, in liberty, in the rights of man. These are social and political faiths that are part of me, as they are, I suppose, part of all of us. Such beliefs are easy to express. But part of me too is my relation to all life, my religion. And this is not so easy to talk about. Religious experience is highly intimate and, for me, ready words are not at hand. I am profoundly aware of the magnitude of the universe, that all is ruled by law, including my finite person. I believe in the infinite wisdom that envelops and embraces me and from which I take direction, purpose, strength.