Classical Logic, Lesson 02

Supposing it then to have been perceived that the operation of Reasoning is in all cases the same, the analysis of that operation could not fail to strike the mind as an interesting matter of inquiry. And moreover, since (apparent) arguments which are unsound and inconclusive, are so often employed, either from error or design; and since even those who are not misled by these fallacies, are so often at a loss to detect and expose them in a manner satisfactory to others, or even to themselves; it could not but appear desirable to lay down some general rules of reasoning applicable to all cases; by which a perv might be enabled the more readily and clearly to state the grounds of his own conviction, or of his objection to the arguments of an opponent; instead of arguing at random, without any fixed and acknowleged principles to guide his procedure. Such rules would be analogous to those of Arithmetic, which obviate the tediousness and uncertainty of calculations in the head; wherein, after much labour, different persons might arrive at different results, without any of them being able distinctly to point out the error of the rest. A system of such rules, it is obvious, must, instead of deserving to be called the “art of wrangling”, be more justly characterised as the “art of cutting short wrangling”, by bringing the parties to issue at once, if not to agreement, and thus saving a waste of ingenuity.

In pursuing the supposed investigation, it will be found that Analysis of every Conclusion is deduced, in reality, from two other propositions; (thence called Premises); for though one of these may be, and commonly is, suppressed, it must nevertheless be understood as admitted; as may easily be made evident by supposing the denial of the suppressed premiss; which will at once invalidate the argument; e.g. if any one, from perceiving that “The world exhibits marks of design.”, infers that “It must have had an intelligent author.”. though he may not be aware in his own mind of the existence of any other premiss, he will readily understand, if it be denied that “Whatever exhibits marks of design must have had an intelligent author.”, that the affirmative of that proposition is necessary to the validity of the argument. Or again, if any one on meeting with “An animal which has horns on the head.” infers that “It is a ruminant.”, he will easily perceive that this would be no argument to any one who should not be aware of the general fact that “All horned animals ruminate.”

An argument thus stated regularly and at full length is called a Syllogism; which therefore is evidently not a peculiar kind of argument, but only a peculiar form of expression, in which every argument may be stated.

When one of the premises is suppressed, (which for brevity’ ”s sake it usually is,) the argument is called an Enthymeme. And it may be worth while to remark, that when the argument is in this state, the objections of an opponent are (or rather appear to be) of two kinds; viz., either objections to the assertion itself, or objections to its force as an argument. For example, in one of the above instances, an atheist may be conceived either denying that the world does exhibit marks of design, or denying that it follows from thence that it had an intelligent author. Now it is important to keep in mind that the only difference in the two cases is, that in the one, the expressed premiss is denied, in the other the suppressed; for the force as an argument of either premiss depends on the other premiss: if both be admitted, the conclusion legitimately connected with them cannot be denied.

It is evidently immaterial to the argument whether the Conclusion be placed first or last; but it may be proper to remark, that a Premiss placed after its Conclusion is called the “Reason” of it, and is introduced by one of those conjunctions which are called causal; viz. “since,” “because,” etc., which may indeed be employed to designate a Premiss, whether it came first or last. The illative conjunctions, “therefore,” etc., designate the Conclusion.

It is a circumstance which often occasions error and perplexity, that both these classes of conjunctions have also another signification, being employed to denote, respectively, Cause and Effect, as well as Premiss and Conclusion: e.g., if I say, “This ground is rich, because the trees on it are flourishing,” or “The trees are flourishing, and therefore the soil must be rich.”, I employ these conjunctions to denote the connection of Premiss and Conclusion; for it is plain that the luxuriance of the trees is not the cause of the soil’s fertility, but only the cause of my knowing it. If again I say, “The trees flourish, because the ground is rich.”, or “The ground is rich, and therefore the trees flourish.”, I am using the very same conjunctions to denote the connection of cause and effect; for in this case, the luxuriance of the trees, being evident to the eye, would hardly need to he proved, but might need to be accounted for.

There are, however, many cases in which the Cause is employed to prove the existence of its Effect; especially in arguments relating to future events; as e.g. when from favourable weather any one argues that the crops are likely to be abundant; the cause and the reason, in that case, coincide. And this contributes to their being so often confounded together in other cases.

Source: Whately, Richard.  Elements of Logic (1870). Book I, Chapter 1, Section 2.

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