What is Lapidem, argumentum ad?

Bishop Berkeley expressed the view that matter does not exist separately from the perception of it. When Boswell told Dr Johnson that this was an idea impossible to refute, the good doctor’s response was to kick against a stone so that his foot rebounded. ‘I refute it thus’, he said. He was not so much refuting it as ignoring it, because the evidence for the existence of the stone, including the sight, sound and feel of a kick against it, is all perceived by the senses.

Dr Johnson’s treatment has given us the name of the argumentum ad lapidem, the appeal to the stone. It consists of ignoring the argument altogether, refusing to discuss its central claim.


He’s a friend of mine. I won’t hear a word spoken against him.

(Top marks for loyalty; none for knowledge.)


An argument or piece of evidence cannot be dismissed because it fails to conform to an existing opinion. Much as we might like to toss out material which offends our ordered view of things, it is a fallacy to suppose that we can do so without cost. By refusing to admit material which may be relevant to a sound conclusion, we proceed in ignorance. Ignorance is more reliable as a source of bliss than of correctness.

The argumentum ad lapidem is most appropriately named after Dr Johnson’s use of it, for it was one of his favourites. His reasoned and balanced view on the freedom of the will, for example, came out as:

We know our will is free, and there’s an end on’t.

(It does tend to finish an argument, as it is meant to.)


Jeremy Bentham described all talk of natural rights as non-sense, and talk of inalienable natural rights as ‘nonsense on stilts’. So much for the American Declaration of Independence.

There are always plenty of stones to kick in fields where proof has no footing. Wherever a belief is indemonstrable, its adherents can use the ad lapidem.


Reason is no guide; you must open your heart… and you will know.

(This is not terribly useful to outsiders looking for the truth of a thing, comforting though it may be to those who know.)


This fallacy occurs in a university setting far more than one might suppose. It is often argued quite seriously in quasi-academic circles that certain books should not be allowed on campus because they propagate error. Speakers are quite frequently shouted down because their audience know they are speaking falsehoods, and do not need to hear the argument. Some student unions actually make a policy of the ad lapidem, refusing to allow a platform on campus for known error – a category which can even include members of the elected government of the country.

A charming version of the fallacy emerged from the pen of Herbert Marcuse. Now forgotten, although he was a high priest of student radicals in the 1960s, his Critique of Pure Tolerance made the interesting point that tolerance can be repressive because it permits the propagation of error. How could we recognize error in order to stop it? Easy. Guess who was going to tell us.

When you yourself employ the ad lapidem, you must do so with a total assurance which suggests that the person who raised the offending fact or argument is totally beyond the pale. Like the judge who once convicted a jury for ‘going against plain evidence’, you should make it clear that he is going against all reason. Your opponent, by going beyond every received opinion and every canon of decency, has rendered his opinion totally unworthy of discussion.


Liberty of expression is one thing; but this is licence!

(‘Licence’ means liberty you don’t approve of.)


Where you have control of events, you can afford to be less subtle: ‘I don’t care what time it is. Get to bed this minute.’