IV. CLASSES OF ARGUMENTS. 1. ON THE BASIS OF FORCE. Demonstra An argument is any proof, -fact, testimony, circumstance, put forward to induce a belief in the truth or falsity of a proposition. Arguments are classified on many bases, the classes thus formed neces- Definition. sarily crossing each other. On the basis of their Probable and force, arguments may be divided into prob- tive. able, sometimes called moral, and certain, also called demonstrative. A probable argument raises some degree, the higher the better, of likelihood or probability. A certain argument establishes the proposition beyond a doubt. In mathematics and the physical sciences, absolute certainty or demonstration is possible. In social science, in legal and political as well as in practical affairs, arguments vary in force from a slight degree of probability to moral certainty. Absolute certainty is such that the opposite is inconceivable. It excludes all doubt. Moral certainty is not absolute certainty. "It is not the exclusion of all doubt. It is that certainty which convinces and directs the understanding and satisfies the reason and judgment of those who act conscientiously upon it; that leads us to act in the gravest concerns of life in our own affairs." 1 Slight The following passages will illustrate the varying degrees of probability in the inferences from observed facts. A hat has been found, Probability. large, fine in quality, three years out of date, covered with closet dust, spotted with grease, the lining 1 Modern Jury Trials, 281. moist and oily, and having bits of gray hair adhering to it : 'The "Holmes picked up the hat and looked at it. owner was highly intellectual, fairly well to do within the last three years, but has fallen upon evil days; had foresight, but is under some evil influence, less now than formerly; .. probably strong drink; this may account for his wife's ceasing to love him; he has retained some degree of self-respect, leads a sedentary life, goes out little, is out of training, is middleaged; has had his hair cut recently, anoints it with lime cream; and it is not probable that he has his house lighted with gas. 991 The inferences in the preceding paragraph are by no means the only way of accounting for the condition of the hat; there is, then, little force in the argument. In the next passage the arguing is more forcible, but the inferences are not absolutely certain. Holmes is investigating a murder case, and is shown the place where the body of the murdered man was found; the fatal wound has been described to him. He reasons thus 2: Strong "These long strides show that the murderer was tall; the blow being on the back of the victim's head on the left side, shows the murderer to be left handed; the slight prints of the right foot in the turf and soft earth, show him to be lame on that foot; these prints show that he wears thick-soled hunting shoes with square toes; this cigar stub and the wrapper near it show that he smokes Indian cigars; the end of the cigar shows his knife to be dull; the ashes on the bark of this tree and the tracks at its foot, indicate that the murderer stood here and smoked for some time, probably while the son and father were quarreling; he uses a cigar-holder, for the stub has not been wet; this stone under which the grass is only slightly pressed, and which corresponds to the wound, was the deadly weapon; 1 Conan Doyle, Adventures of the Blue Carbuncle. 2 See Sign, Page 173. the murderer is an Australian, for he answered the Australian call, 'Cooee!' He wears a gray cloak — the gray thing which the son testifies to having seen on the sward." 1 In his Origin of Species 2 Darwin presents arguments leading to practical certainty that beauty of form and beauty of color existed prior to the creation of man, and are therefore independent of man's gratifica Certainty. tion. The same practical certainty is found Practical in the following argument that radiant heat and radiant light are the same thing, or only variations of the same thing, in Tait's Recent Advances: "The radiant heat from the sun goes along with the light from the sun, and when you shut one off,-put a screen so as to intercept the one, the other is intercepted at the same time. In the case of a solar eclipse, you have the sun's heat as long as you see the smallest portion of the sun's disk. The instant the last portion of the disk is obscured, the heat disappears with the light. That shows that the heat and the light take not only the same course, but also the same time to come to us. If the one lagged ever so little behind the other, if the heat disappeared sooner than the light, or the light sooner than the heat, - it would show that though they both moved in straight lines, the one moved faster than the other; but the result of observation is that we find so far as our most delicate measurements show, that heat and light are simultaneously intercepted." 3 To know the difference between arguments that establish a proposition with certainty, and those that establish it with varying degrees of probability, and to estimate correctly the degree of probability, is of prime Importance importance. In practical affairs, in matters of Knowing affecting the ownership of great estates and the lives of those accused of crime, men are guided almost entirely by inferences from facts. 1 Conan Doyle, Boscombe Valley Mystery. Force. 2 Chap. vi. "You cannot walk a block without being convinced through circumstantial evidence. You cannot live a day of your life without relying on circumstantial evidence. You got up yesterday morning and saw snow. It was as surely snow as if you had seen it fall. You knew it had fallen. It is here a fact. You know a cat has crossed it You see in it the track of a cat. in that direction. A man drives by with a horse covered with You see that the foam. You know he has driven rapidly. horse is shod. You did not see the shoe nailed on, but you know that it is the work of a man. Force Differs Minds. Facts affording arguments practically certain to one class of men or at one time, have much less force as arguments to other men or at another time. It would be difficult to fix a criterion by which the force to Different of all arguments could be measured by all men at all times. When the mind is satisfied that there is sufficient proof, "hypothesis 2 becomes induction. This point will be reached much more readily some minds than by others. Professor Huxley regarded the proposition that modern horses are descended from small five-toed progenitors as demonstratively estab lished, while many others still looked upon evolution as a very slenderly supported hypothesis."3 Macaulay thought that he had conclusively proved the identity of Junius with Sir Philip Francis. The facts and hypotheses are thus stated by Wharton a : "The number of hypotheses increases with the complication of the case. If, for instance, Sir Philip Francis's title to the authorship of Junius's letters is under investigation, we have a series of concentric hypotheses each of which is pertinent and the innermost of which closely surrounds the point of identity. It is pertinent to argue that the author of the letters during the Chatham and Grafton ministries, was familiar with English 2 Pages 113, 129. 1 Modern Jury Trials, 290. 8 Ballantine, Inductive Logic, 117. 4 Law of Evidence, 33. public life; that he possessed a practiced pen; that he was cognizant of the traditions of the war office; that his animosity to Lord Mansfield and his attachment to Lord Chatham were strong; that he had cogent motives for concealing, both at the particular period and for years afterwards; that he ceased to write about 1773; that his handwriting had certain marked peculiarities. Each of these hypotheses being pertinent, it is relevant to prove that Sir Philip Francis was, during the period when the Junius letters appeared, familiar with English public life; that his style was polished, vigorous and not unlike that of Junius; that he had been some time a clerk in the war office; that his political relations repelled him from Lord Mansfield, and connected him with Lord Chatham; that to him discovery would be political ruin; that at about the time the Junius letters closed, he left the country; that his handwriting was strikingly like that of Junius." In spite of these facts, however, it is not now generally believed by those who have investigated the matter, that Francis wrote The Letters of Junius. 2. BASIS OF USE. On the basis of their use, arguments are direct or indirect. Direct arguments aim straight at a definite and desired conclusion. They are positive, candid, apparent. By them the reasoner seeks openly and in propria 1 The division of proofs into direct and indirect is so important that I wish to suggest for class work the following classification which contains its own explanation: (A) Direct proofs, proofs for one's own proposition (these may be a priori, by sign, by example or by analogy). (B) Indirect proofs (of one's own proposition): 1. A direct overthrow of the opponent's proposition; that is, a proof of any of the four sorts against the opponent's proposition; or 2. An indirect overthrow of the opponent's proposition; that is, the refuting of a proof offered (or imagined to be offered); (a) in favor of the opponent's proposition, or (b) against one's own proposition. Educational Review, October, 1897, 288. |