(3) The precedent may (as has been already remarked) be a general idea, or may be an individual idea or object. If S A has occurred frequently it is certain to be generalised, and so may form a maxim, a law, a rule, an induction, &c. But one well-observed precedent is enough to suggest a conclusion, if there has been no experience to the contrary. There is therefore no dialectical difference between arguing from a general idea (class notion) to an individual or subordinate idea, and arguing from one individual to another. Comparison and inference occur in both.
(4) After separating A from S care should be taken that it is A and not S that is used to generate I. Examples are plentiful of theorems in which S and A change parts, which invalidates the conclusion. Other errors in stating theorems intended to be arguments will be noticed under the head of 'Fallacies.'
The following is an argument conformable to the above rules.
| Tyrants | deserve death |
| Caesar was a tyrant | no doubt he deserved death |
This square mode of stating the argument is adapted from the general type, and brings out the mutual relations of the compared parts better than the three-lined arrangement. The word 'therefore,' which usually introduces a logical conclusion, is ambiguous. It may mean that the antecedents are the causes of the fact mentioned in the conclusion, or merely that the antecedents are the reasons why we believe the conclusion. The former is the scientific 'therefore,' the latter is the purely dialectical. I shall generally omit the illative word, and print conclusions in italics, besides entering them invariably in the fourth compartment of the parallel when this arrangement is adopted.
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.