I've seen philosophical arguments descriped as 'argumentum ad lapidem', but never quite understood what the criticism is trying to indicate. As best I can tell, it's a dismissal of an argument with no good justification. Could anybody expand a little on the precise nature of this logical fallacy?
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According to the Wikipedia definition:
Ad lapidem (Latin: "to the stone") is a logical fallacy that consists in dismissing a statement as absurd without giving proof of its absurdity.
The Latin name is doubly confusing in that it has a fairly modern origin and in that it relates to a specific example:
The name of this fallacy is attributed to Dr. Samuel Johnson, who refuted Bishop Berkeley's immaterialist philosophy (that there are no material objects, only minds and ideas in those minds), by kicking a large stone and asserting, "I refute it thus."
Now as an effective and memorable rhetorical tactic, Dr. Johnson found an excellent way to make his point. The problem comes when examining the content of his logical argument. What he suggests by his demonstration is that of course there are material objects: we can feel them and see them and interact with them. But if Bishop Berkeley objected that the sensation of feeling, seeing and interacting with objects could simply be the result of, for instance, imagination, Dr. Johnson would need to deal directly with that objection. (I don't know either if Bishop Berkeley made such an objection or if Dr. Johnson offered a response, but for the sake of the illustration, let's assume the first did and the later didn't.)
It's not always incorrect to use arguments that are in the form of logical fallacies, as the example of kicking a stone illustrates. For most of us, the simple demonstration is effective at getting the point across. But when you consider the opposite viewpoint, ad lapidem does not satisfy an objection or compel agreement. It may be useful for scoring points in a debate, but not useful in either finding common ground or discovering the truth. Pointing out a fallacious argument should redirect the proponent of the position to try another method of arguing that does not entail a logical fallacy.
Dr. Johnson could have corrected his argumentum ad lapidem (and perhaps he did) by suggesting some other reason not to accept immaterialism.