“SPAN ID=What_we_should_do> What we should do, I suggest, is to give up the idea of ultimate sources of knowledge, and admit that all knowledge is human; that it is mixed with our errors, our prejudices, our dreams, and our hopes; that all we can do is to grope for truth even though it be beyond our reach. We may admit that our groping is often inspired, but we must be on our guard against the belief, however deeply felt, that our inspiration carries any authority, divine or otherwise. If we thus admit that there is no authority beyond the reach of criticism to be found within the whole province of our knowledge, however far it may have penetrated into the unknown, then we can retain, without danger, the idea that truth is beyond human authority. And we must retain it. For without this idea there can be no objective standards of inquiry; no criticism of our conjectures; no groping for the unknown; no quest for knowledge. </SPAN”
Introduction "On The Sources of Knowledge and of Ignorance" Section XVII, p. 30 Variant translation: I believe it is worthwhile trying to discover more about the world, even if this only teaches us how little we know. It might do us good to remember from time to time that, while differing widely in the various little bits we know, in our infinite ignorance we are all equal.
If we thus admit that there is no authority beyond the reach of criticism to be found within the whole province of our knowledge, however far we may have penetrated into the unknown, then we can retain, without risk of dogmatism, the idea that truth itself is beyond all human authority. Indeed, we are not only able to retain this idea, we must retain it. For without it there can be no objective standards of scientific inquiry, no criticism of our conjectured solutions, no groping for the unknown, and no quest for knowledge.
Conjectures and Refutations: The Growth of Scientific Knowledge (1963)
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Karl Popper 82
Austrian-British philosopher of science 1902–1994Related quotes

Variant translation: The more we learn about the world, and the deeper our learning, the more conscious, clear, and well-defined will be our knowledge of what we do not know, our knowledge of our ignorance. The main source of our ignorance lies in the fact that our knowledge can only be finite, while our ignorance must necessarily be infinite.
Conjectures and Refutations: The Growth of Scientific Knowledge (1963)
Context: The more we learn about the world, and the deeper our learning, the more conscious, specific, and articulate will be our knowledge of what we do not know, our knowledge of our ignorance. For this, indeed, is the main source of our ignorance — the fact that our knowledge can be only finite, while our ignorance must necessarily be infinite.

“Our weapon is our knowledge. But remember, it may be a knowledge we may not know that we possess.”
Source: The A.B.C. Murders

1830s, The American Scholar http://www.emersoncentral.com/amscholar.htm (1837)
Context: We will walk on our own feet; we will work with our own hands; we will speak our own minds... A nation of men will for the first time exist, because each believes himself inspired by the Divine Soul which also inspires all men.

Speech at the National Press Club (2004)

“All we know of the truth is that the absolute truth, such as it is, is beyond our reach.”
De Docta Ignorantia (On Learned Ignorance) (1440)

Source: Julian and Maddalo http://www.bartleby.com/139/shel115.html (1819), l. 170