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The Role of Doubt in Science

Richard P. Feynman

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Summary: 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.

The scientist has a lot of experience with ignorance and doubt and uncertainty, and this experience is of very great importance, I think. When a scientist doesn't know the answer to a problem, he is ignorant. When he has a hunch as to what the result is, he is uncertain. And when he is pretty darned sure of what the result is going to be, he is in some doubt. 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.
Now, we scientists are used to this, and we take it for granted that it is perfectly consistent to be unsure - that it is possible to live and not know. But I don't know whether everyone realizes that this is true. Our freedom to doubt was born of a struggle against authority in the early days of science. It was a very deep and strong struggle. Permit us to question -- to doubt, that's all -- and not to be sure. ...

Through all ages, men have tried to fathom the meaning of life. They have realized that if some direction or meaning could be given to our actions, great human forces would be unleashed. So, very many answers must have been given to to the question of the meaning of it all. But they have been of all different sorts, and the proponents of one answer have looked with horror at the actions of the believers in another. Horror, because from a disagreeing point of view all the great potentialities of the race were being channeled into a false and confining blind alley. ... The dream is to find the open channel.

What, then, is the meaning of it all? What can we say to dispel the mystery of existence ?

If we take everything into account, not only what the ancients knew, but all of what we know today that they didn't know, then I think we must frankly admit that we do not know.

But in admitting this, we have probably found the open channel.

This is not a new idea; this is the idea of the age of reason. This is the philosophy that guided the men who made the democracy that we live under. The idea that no one really knew how to run a government led to the idea that we really should arrange a system by which new ideas could be developed, tried out, tossed out, more new ideas brought in: a trial and error system. This method was a result of the fact that science was already showing itself to be a successful venture at the end of the 18th century. Even then it was clear to socially minded people that the openness of the possibilities was an opportunity, and that doubt and discussion were essential to progress into the unknown. If we want to solve a problem that we have never solved before, we must leave the door to the unknown ajar. ...

It is our responsibility to leave the men of the future with a free hand. In the impetuous youth of humanity, we can make grave errors that can stunt our growth for a long time. This we will do if we, so young and ignorant, say we have the answers now, if we suppress all discussion, all criticism, saying, 'This is it, boys! Man is saved!' Thus we can doom man for a long time to the chains of authority, confined to the limits of our present imagination. It has been done so many times before.

It is our responsibility as scientist, knowing the great progress and great value of a satisfactory philosophy of ignorance, the great progress that is the the fruit of freedom of thought, to proclaim the value of this freedom, to teach how doubt is not to be feared but welcomed and discussed, and to demand this freedom as our duty to all coming generations.



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Quotations on doubt

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To have doubted one's own first principles is the mark of a civilized man.
- Legal Papers, 1920.
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... If I let myself believe anything on insufficient evidence, there may be no great harm done by the mere belief; it may be true after all, or I may never have occasion to exhibit it in outward acts. But I cannot help doing this great wrong towards Man, that I make myself credulous. The danger to society is not merely that it should believe wrong things, though that is great enough; but that it should become credulous.
- W.K. Clifford, quoted in Science and Human Values, 1956.
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Preserve in everything freedom of mind. Never spare a thought for what men may think, but always keep your mind so free inwardly that you could always do the opposite.
- St. Ignatus Loyola, Spiritual Exercises, 1548.
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The first key to wisdom is assiduous and frequent questioning ... For by doubting we come to inquiry, and by inquiry we arrive at truth.
- Perter Abelard, Yes and No, c. 1120.
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The most dangerous tendency of the modern world is the way in which bogus theories are given the force of dogma.
- Jean Danielou, The Lord of History, 1958.
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Outside the practice of science itself, scientists have sometimes been the greatest offenders in adhering to dogmatic ideas against all the evidence.
- Mary B. Hesse, Science and the Human Imagination, 1955.
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True Science teaches, above all, to doubt, and to be ignorant.
- Miguel de Unamuno, The Tragic Sense of Life.
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Most institutions demand unqualified faith; but the institution of science makes skepticism a virtue.
- Robert King Merton 1910-, Social Theory and Social Structure, 1962.
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In science, self-satisfaction is death. Personal self-satisfaction is the death of the scientist. Collective self-satisfaction is the death of the research. It is restlessness, anxiety, dissatisfaction, agony of mind that nourish science.
- Jacques Monod 1910-1977, New Scientist, 1976.
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My teacher, Hopkins, often commented on the craving for certainty that led so many physicists into mysticism or into the Church and similar organisations ... Faith seems to be an occupational hazard for physicists.
-Norman Wingate Pirie, Penguin New Biology, 1954.

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