What have great philosophers such as Bertrand Russell, George Berkeley, Lewis Carroll, and Charlie Chan said about logic, fallacies, and the importance of logical thinking in life? The quotations below are arranged in alphabetical order by author, from top to bottom. Click on the author's name in the Index just beneath to go directly to that author's quote. If you know of a good quote that should be here, please send it to the Fallacy Files.

Bentham, Jeremy Berkeley, George Carroll, Lewis Chan, Charlie
Epictetus Fischer, David Hackett Geach, Peter Hillis, Burton
Hitchens, Christopher Huxley, Thomas Henry Jefferson, Thomas Laplace, Marquis de
Mill, John Stuart Nickell, Joe Peirce, Charles Sanders Russell, Bertrand
Truzzi, Marcello Voltaire Wieseltier, Leon Wolff, Christian

Without a popular assembly taking an effective part in the government and publishing its debates, and without free discussion through the medium of the press, there is no demand for fallacies. Fallacy is fraud; and fraud is useless when everything is done by force.

Source: Jeremy Bentham, Bentham's Handbook of Political Fallacies (Apollo Editions, 1971), p. 246.

Surely it wouldn’t be such a deplorable loss of time if a young gentleman [or young lady] spent a few months [or a few years] on the much despised and decried art of Logic―a surplus of logic is by no means the prevailing nuisance of this age!

Source: George Berkeley, Alciphron or: The Minute Philosopher, Fifth Dialogue

Once master the machinery of Symbolic Logic, and you have a mental occupation always at hand, of absorbing interest, and one that will be of real use to you in any subject you may take up. It will give you clearness of thought—the ability to see your way through a puzzle—the habit of arranging your ideas in an orderly and get-at-able form—and, more valuable than all, the power to detect fallacies, and to tear to pieces the flimsy illogical arguments, which you will so continually encounter in books, in newspapers, in speeches, and even in sermons, and which so easily delude those who have never taken the trouble to master this fascinating Art.

Source: Lewis Carroll, Symbolic Logic, Part 1: Elementary (Fourth Edition) (Dover, 1958), p. xvii.

Charlie Chan: Hasty conclusion like toy balloon: easy blow up, easy pop.

Source: Robert Ellis, Helen Logan & Edward T. Lowe Jr., Charlie Chan at the Race Track

Logic is not everything. But it is something—something which can be taught, something which can be learned, something which can help us in some degree to think more sensibly about the dangerous world in which we live.

Source: David Hackett Fischer, Historians' Fallacies: Toward a Logic of Historical Thought (Harper & Row, 1970), p. 306.

When one of the company said to him [Epictetus], "Convince me that logic is necessary."―Would you have me, he said, demonstrate it to you? "Yes." Then I must use a demonstrative form of argument. "Granted." And how will you know, then, whether I argue sophistically? On this, the man being silent, You see, says he, that, even by your own confession, logic is necessary; since without it, you cannot even learn whether it be necessary or not.

Source: Epictetus, Discourses, translated by Elizabeth Carter & Thomas Wentworth Higginson, Book 2, Chapter 25

I have been in love with logic ever since my father started me on logic in my teens. Logic of itself cannot give anyone the answer to any questions of substance; but without logic we often do not know the import of what we know and often fall into fallacy and inconsistency.

Source: Peter Geach, quoted in Steve Pyke, Philosophers (1996).

There's a mighty big difference between good, sound reasons and reasons that sound good.

Source: Burton Hillis, cited in Laurence J. Peter, Peter's Quotations: Ideas for Our Time (1977), p. 425.

What can be asserted without evidence can also be dismissed without evidence.

Source: Christopher Hitchens, God is Not Great (2007), p. 150.

[S]cience is simply common sense at its best; that is, rigidly accurate in observation, and merciless to fallacy in logic.

Source: Thomas Henry Huxley, The Crayfish, Chapter 1

…[I]n a republican nation whose citizens are to be led by reason and persuasion and not by force, the art of reasoning becomes of first importance.

Source: Thomas Jefferson, From Thomas Jefferson to David Harding, 20 April 1824, National Archives

The mind has its illusions as the sense of sight; and in the same manner that the sense of feeling corrects the latter, reflection and calculation correct the former.

Source: Pierre Simon, Marquis de Laplace, A Philosophical Essay on Probabilities (Dover, 1952), p. 160.

In attempting to establish certain general distinctions which shall mark out from one another the various kinds of Fallacious Evidence, we propose to ourselves an altogether different aim from that of several eminent thinkers, who have given, under the name of Political or other Fallacies, a mere enumeration of a certain number of erroneous opinions; false general propositions which happen to be often met with…. Logic is not concerned with the false opinions which people happen to entertain, but with the manner in which they come to entertain them.

Source: John Stuart Mill, A System of Logic, Book V, Chapter II, § 1

The person who thinks he can't be fooled has just fooled himself.

Source: Joe Nickell in David Grossberg, "Joe Nickell, Autograph Detective", Autograph Collector, April/May 2007, pp. 78-80.

Few persons care to study logic, because everybody conceives himself to be proficient enough in the art of reasoning already. But I observe that this satisfaction is limited to one's own ratiocination, and does not extend to that of other men.

Source: Charles Sanders Peirce, "The Fixation of Belief", Popular Science Monthly 12 (November 1877), pp. 1-15.

Logical errors are, I think, of greater practical importance than many people believe; they enable their perpetrators to hold the comfortable opinion on every subject in turn.

Source: Bertrand Russell, A History of Western Philosophy (Book-of-the-Month Club, 1995), p. 93.

An extraordinary claim requires extraordinary proof.

Source: Marcello Truzzi, "On the Extraordinary: An Attempt at Clarification", Zetetic Scholar: An Independent Scientific Review of Claims of Anomalies and the Paranormal, Vol. 1, No. 1 (1978), p. 11. This not-so extraordinary claim was popularized by Carl Sagan in the form: "Extraordinary claims require extraordinary evidence."

L'Abbé: …[U]n bon mot ne prouve rien.

Le Comte: Cela est vrai; mais un bon mot n’empéche pas qu’on ne puisse avoir raison.


L'Abbé: A witty remark proves nothing.

Le Comte: That's true; but a witty remark doesn't stop you from using your reason.

Source: Voltaire, Le Dîner du Comte de Boulainvilliers, Second Entretien (1728)

Do not look down on nonsense. Nonsense comes to power. Nonsense murders millions. It prospers if we are too exquisite, too intellectually respectable, to bother with it.

Source: Leon Wieseltier, "Reason and the Republic of Opinion", New Republic, 11/11/2014

…[L]east of all can we advance, that the study and practice of Logic are unnecessary. For when a man has not a distinct knowledge of the Rules by which the understanding is directed, he may err in the use of his natural powers; as we have instances of those illogical reasonings, by which learned men are sometimes led into error.

Source: Christian Wolff, Logic (1770), p. 216.

Acknowledgment: Thanks to David Marans in whose useful Logic Gallery I found the Berkeley quote, and who also called my attention to the Wolff quote.

Source: David Marans, Logic Gallery: Ancient Greece to the 21st Century, Third Edition, Enlarged (PDF)