Man errs as long as he strives – Johann Wolfgang von Goethe



We have found it of paramount importance that in order to progress we must recognize the ignorance and leave room for doubt. Scientific knowledge is a body of statements of varying degrees of certainty – some most unsure, some nearly sure, none absolutely certain.

Richard Feynman, The Value of Science


It has always been asked in the spirit of: ‘What are the best sources of our knowledge – the most reliable ones, those which will not lead us into error, and those to which we can and must turn, in case of doubt, as the last court of appeal?’ I propose to assume, instead, that no such ideal sources exist – no more than ideal rulers – and that all ‘sources’ are liable to lead us into errors at times. And I propose to replace, therefore, the question of the sources of our knowledge by the entirely different question: ‘How can we hope to detect and eliminate error?’ The question of the sources of our knowledge, like so many authoritarian questions, is a genetic one. It asks for the origin of our knowledge, in the belief that knowledge may legitimize itself by its pedigree. The nobility of the racially pure knowledge, the untainted knowledge, the knowledge which derives from the highest authority, if possible from God: these are the (often unconscious) metaphysical ideas behind the question. My modified question, ‘How can we hope to detect error?’ may be said to derive from the view that such pure, untainted and certain sources do not exist, and that questions of origin or of purity should not be confounded with questions of validity, or of truth. …. The proper answer to my question ‘How can we hope to detect and eliminate error?’ is I believe, ‘By criticizing the theories or guesses of others and – if we can train ourselves to do so – by criticizing our own theories or guesses.’ …. So my answer to the questions ‘How do you know? What is the source or the basis of your assertion? What observations have led you to it?’ would be: ‘I do not know: my assertion was merely a guess. Never mind the source, or the sources, from which it may spring – there are many possible sources, and I may not be aware of half of them; and origins or pedigrees have in any case little bearing upon truth. But if you are interested in the problem which I tried to solve by my tentative assertion, you may help me by criticizing it as severely as you can; and if you can design some experimental test which you think might refute my assertion, I shall gladly, and to the best of my powers, help you to refute it.’

Karl Popper, Knowledge Without Authority


The gods did not reveal, from the beginning,
All things to us; but in the course of time,
Through seeking we may learn, and know things better.
But as for certain truth, no man has known it,
Nor will he know it; neither of the gods,
Nor yet of all things of which I speak.
And even if by chance he were to utter
The perfect truth, he would himself not know it:
For all is but a woven web of guesses.

Xenophanes (from Karl Popper’s In Search of a Better World)


Ignorance more frequently begets confidence than does knowledge: It is those who know little, and not those who know much, who so positively assert that this or that problem will never be solved by science.

Charles Darwin, The Decent of Man


The day may come when the rest of the animal creation may acquire those rights which never could have been withholden from them but by the hand of tyranny. The French have already discovered that the blackness of the skin is no reason why a human being should be abandoned without redress to the caprice of a tormentor. It may one day come to be recognised that the number of the legs, the villosity of the skin, or the termination of the os sacrum, are reasons equally insufficient for abandoning a sensitive being to the same fate. What else is it that should trace the insuperable line? Is it the faculty of reason, or perhaps the faculty of discourse? But a fullgrown horse or dog is beyond comparison a more rational, as well as a more conversable animal, than an infant of a day, or a week, or even a month, old. But suppose they were otherwise, what would it avail? The question is not, Can they reason? nor Can they talk? but, Can they suffer?

Jeremy Bentham, The Principles of Morals and Legislation


Questions of ultimate ends are not amenable to direct proof. Whatever can be proved to be good, must be so by being shown to be a means to something admitted to be good without proof. The medical art is proved to be good by its conducing to health; but how is it possible to prove that health is good?

John Stuart Mill, Utilitarianism


Our moral faculty….is a branch of our reason, not of our sensitive faculty; and must be looked to for the abstract doctrines of morality, not for perception of it in the concrete.

John Stuart Mill, Utilitarianism


The creed which accepts as the foundation of morals, Utility, or the Greatest Happiness Principle, holds that actions are right in proportion as they tend to promote happiness, wrong as they tend to produce the reverse of happiness. By happiness is intended pleasure, and the absence of pain; by unhappiness, pain, and the privation of pleasure. To give a clear view of the moral standard set up by the theory, much more requires to be said; in particular, what things it includes in the ideas of pain and pleasure; and to what extent this is left an open question. But these supplementary explanations do not affect the theory of life on which this theory of morality is grounded – namely, that pleasure, and freedom from pain, are the only things desirable as ends; and that all desirable things (which are as numerous in the utilitarian as in any other scheme) are desirable either for the pleasure inherent in themselves, or as means to the promotion of pleasure and the prevention of pain.

John Stuart Mill, Utilitarianism


Toleration is the necessary consequence of realizing our human fallibility: to err is human, and we do it all the time. So let us pardon each other’s follies. This is first principle of natural right.

Voltaire (Karl Popper’s translation)


…magic is only a word, not an answer. In itself, magic is a word which explains nothing.

Jacob Bronowski, The Ascent of Man


All silencing of discussion is an assumption of infallibility.

John Stuart Mill, On Liberty


Religious suffering is, at one and the same time, the expression of real suffering and protest against real suffering. Religion is the sigh of the oppressed creature, the heart of a heartless world, and the soul of soulless conditions. It is the opium of the people. The abolition of religion as the illusory happiness of the people is the demand for their real happiness. To call on them to give up their illusions about their condition is to call on them to give up a condition that requires illusions. The criticism of religion is, therefore, in embryo, the criticism of that vale of tears of which religion is the halo. Criticism has plucked the imaginary flowers on the chain not in order that man shall continue to bear that chain without fantasy or conclusion, but so that he shall throw off the chain and pluck the living flower.

Karl Marx, A Contribution to the Critique of Hegel’s Philosophy of Right


Whenever we read the obscene stories, the voluptuous debaucheries, the cruel and torturous executions, the unrelenting vindictiveness, with which more than half the Bible is filled, it would be more consistent that we called it the word of a Demon, than the word of God. It is a history of wickedness that has served to corrupt and brutalise mankind: and for my own part, I sincerely detest it, as I detest everything that is cruel.

Thomas Paine, The Age of Reason