An idea once generated in the intellect is not to be erased at pleasure. It can be obliterated only by the process of forgetting. If after we have formed a dialectical conclusion we meet with evidence that contradicts it, the only result of that evidence is to affix a mark of falsity to the conclusion, so that as often as it is recollected the stigma is recollected too, and neutralises the effect of the idea. A negative or destructive argument is thus, plasmically speaking, a positive addition to the idea it seeks to efface. For the time being it renders the idea more conspicuous, as the word CANCELLED stamped in large letters across a document makes it more evident than it was before; but no doubt the stigmatising of an idea hastens the process of oblivion, for we thenceforth bestow less attention upon it. Stigmatic arguments are not another species, but merely the ordinary constructive arguments used for a particular purpose. Suppose we have inferred from the general resemblance of the earth to the moon that the latter is inhabited, we stigmatise this belief by such an argument as-- Without air | animals cannot live ----------------------------+----------------------------------- There is no air in the moon | _there can be no life in the moon_ There is an exception to the rule that argument is superfluous when the speaker has already verified the conclusion. It is when he is addressing a person who has not had the same experience as himself and who doubts his word. The speaker may then resort to arguments drawn from antecedents recognised by the hearer, if any such are applicable to the subject. But a fact may be truly reported though neither the witness nor a sceptical hearer can find dialectical antecedents to prove it, for there may be no relation between the fact in question and any prior knowledge they possess, or they may not be able to find the relation. This brings us again to that view of the intellect which represents it as artificial and limited by experience. Man is rational only on matters familiar to him; in utterly novel circumstances he is irrational, and must fall back for guidance on his general mental sentiment, or the advice of persons more experienced than himself. XIX--HYPOTHETICAL ARGUMENTS It is allowable to imagine ourselves placed in circumstances not yet realised, or in possession of information not yet acquired, and to anticipate or rehearse the reasoning we should employ under the supposed conditions. Such arguments take in language a conditional or hypothetical phraseology. The case may be entirely fictitious, but I cannot find a valid instance of a whole precedent being fictitious. Its dubiety turns on our knowledge or ignorance of the applicate. Has a subject such or such an attribute? Then it may be applied to illustrate a certain case. 'If it is true that Damon and Pythias are inseparable, _then Pythias must be in town_, for I have just seen Damon.'