These five principles may be reduced to two, which are: negatively, that none of the ante cedents of an effect that can be dispensed with without preventing the effect is the cause, and positively, that every antecedent of an effect that cannot be dispensed with without prevent ing the effect is the cause or part of the cause. These principles may be proved by reference to two principles which are the ultimate founda tion of all arguments from Experience. These are the law of Universal Causation which may be expressed by saying that "Every event has a cause," and the law of the Uniformity of Causes which may be expressed by saying that "Like causes produce like effects in like circum stances." It is in accordance with these principles that investigations are carried on in every branch of science that has to do with tracing the relation of cause and effect, and establishing principles based thereon.
We use the argument from Example when we cite as a reason for the truth of a general proposition a number of observed or known facts similar to those summed up in the thesis, the facts set forth being examples of the general truth they are cited to prove. Thus, we argue that all horned animals are ruminant because the ox, the sheep, the deer and other horned animals are rumi nant. In an argument of this kind the reason is seldom stated in full and the principle is seldom stated at all. When the proposition to be proved is universal, the advocate relies on the implied assumptions that no negative ex ample has been found and that the search has been exhaustive. He is usually content to state one or more positive instances and shift on his opponent the burden of showing an exception, or that the search has not been complete. The argument may be stated in full as follows: Thesis: All horned animals are ruminant; Reason: Because A, B, C and a number of other horned animals are ruminant and no horned animal has been found, after due search, that is not ruminant; Principle: What ever has been found to be true in a number of instances of a phenomenon and never found to be false, after due search, in any, is true of all.
In like manner we may argue that all men are mortal, that unsupported bodies fall to the ground, that food is necessary to animal life, that the price of protected manufactures tends to decline.
In an argument from Analogy points of resemblance between two things are relied on to prove that the resemblance extends further than is actually known or observed. Thus, when we argue that a given specimen of handwriting was written by a particular person because it resembles handwriting that is known to have been written by that person, we employ an argument from Analogy. The principle upon which this argument is based may be stated as follows: `Whatever is true of a thing is true of what essentially resembles it. It is sometimes said that no thesis can be proved conclusively by analogical evidence, but if es sential resemblance can be shown, if, in other words, the analogy is complete, the argument may be as conclusive as any other. In many
cases in which the argument from analogy is employed it is impossible to show essential resemblance, and, of course, the thesis cannot be asserted as more than probably true. Thus, in the argument that Mars is inhabited because of its many points of resemblance to the earth it is impossible to say that the thesis is even probably true, since there are so many points of essential difference and so many essential points as to which it is unknown whether Mars resembles the earth or not. To justify a prob able conclusion there must be more points of resemblance than of difference and the points as to which we do not know whether the two things compared agree or differ should be con sidered as points of difference. Moreover, of all possible points of resemblance and of dif ference only those should be considered which are essential, that is to say, which have a direct bearing on the question to be proved. The principle upon which we rely in using a prob able argument from analogy may be stated as follows: °When two things resemble each other in a preponderating number of essential particulars what is true of one is probably true of the other." The arguments from Example and from An alogy depend in the last analysis upon causa tion. The uniformity of the facts in the one case and the essential similarity of the facts in the other lead us to infer a cause which, although not known, is assumed to exist to account for the fact or class of facts to be proved.
Cause to An argument from Cause to Effect is one in which the existence of a known cause is given as a reason to prove an effect, as when we argue that a man will die because he is afflicted with a particular disease. Such an argument Army be only prob able since the action of every cause is liable to be frustrated by other agencies, and it ap proaches to conclusiveness in so far as it can be shown that no other agency is operating or will operate to prevent the effect. When an argument of this kind is employed the as sumptions relied on are that the circumstance given as a reason has been found to be ade quate to produce the alleged effect, that its action cannot be frustrated and that it will be followed by its effect in this case as in the former case or cases, or in other words, that like causes produce like effects. The argument may be expressed in full as follows: T: A will die; R: Because he is afflicted with X, a cause of death that cannot be frustrated; P: Every cause that cannot be frustrated will be fol lowed by its effect. The argument may be stated more simply by using as a principle the law of the particular effect: T: A will die; R: Because he is afflicted with X; P: Because all who are afflicted with X die. In like manner we may argue from motives to actions which they tend to produce.