Every argument, whatever be the matter of it, consists in bringing a Case under a Precedent, and applying to the case ideally the better knowledge possessed of the precedent. The Conclusion (also called Inference or Deduction) is the result of this application, and is always an addition to our stock of ideas.
A conclusion has never the same reality as actual experience. It is not 'true' in that sense, though it may be 'morally' true, that is, we are ready to act upon it without hesitation—to stake our life or fortune on it. As regards actual or experienced fact there can be no argument, since it is useless to 'predict' what we already know.
Academical logicians have a doctrine the reverse of this. They assert that their syllogisms yield conclusions that are always as certain as the premises. Grant their premises and you are obliged to accept their conclusions. This is so, because a regular syllogistic conclusion is simply a restating in other words of the information, or part of the information, already contained in the premises. If the syllogism has any use at all, it is merely as an aid to recollection; no new idea is generated by it. It is needless to insist on a fact so notorious as that ordinary rational conclusions—those that form the staple of our daily thought—are not by any means so certain as the data from which they are drawn. For example, the sky is red and lowering this evening, and we conclude therefrom that the weather will be bad to-morrow. There is no doubt about the present aspect of the sky, but much doubt about the inference.
The form of an act of reasoning or argumentation may be rendered plainer by a diagram.
| S | A |
| C | I |
S A represents the precedent. S is the Subject or body of the precedent; A (the Applicate) is one property, or a part, or a relation of S abstracted from the rest to illustrate a case. C is the case; I is the conclusion (or inference). I results from imagining C to be associated with a property or relation similar to A. The sum of our I's constitutes what we know of the world and man before we were born, of what is taking place in other parts of the world or universe, of what may take place in the future, and of the concealed and inaccessible parts of present objects. This is true not only of the results of our own reasoning but of what we have learned as verified knowledge from others, for the interpretation of language is, in the last analysis, a rational conclusion.
All the parts of an argument exist in the mind, but they are not always expressed in language. When treated dialectically the implicit members are expressed, and the terms arranged so as to show as clearly as possible the nature of the argument. The following are the points most necessary to be observed in constructing or analysing an argument.
(1) C must resemble S, for that is the basis of the argument. If C is not felt to be like S, or (as sometimes happens) is explicitly declared to be unlike S, there can be no conclusion. The precedent is not applicable to the case. A may, or may not, be associated with S; that is to say, a verbal negation may appear in the statement of the relation of S to A, but there must be no negation with respect to the relation of C to S.
The resemblance of C to S may, however, vary in degree from the faintest analogy to community of species. The difference between them may far outweigh their resemblance. There may even be no material likeness, but only a similarity of function, or position, or of any the most trivial attribute. Only it is to be observed that the kind and degree of resemblance between S and C determine the kind and degree of resemblance between A and I. We must not infer specifically unless the case is specifically like the precedent. In all other instances we can only infer proportionally or by transfusion.
(2) None of the antecedents must be a verbal or identical proposition, that is, a proposition which merely substitutes one name or nominal phrase for another; nor must the case be merely the precedent expressed in other words, or the precedent a paraphrase of the case. In any of these circumstances one of the elements of the argument is wanting; we have two names for one thing or two propositions giving the same information.