<) not found.[endif]--> Appl

Weaver Chpt. 5

Excerpt from Richard M. Weaver’s
Rhetoric and Handbook,
Chapter 5

The Enthymeme

It is natural for the syllogism to appear at first a somewhat cumbersome and artificial mode of expressing our everyday reasoning. We pointed out at the beginning, however, that to make sure of the correctness of arguments, it is necessary to be both full and explicit in statement, and the syllogism is merely a fully expanded form which we use when we undertake to prove one proposition by other propositions. It is true, none the less, that actual arguments do not always appear in this fully expanded form. In perhaps a majority of the instances, they appear with one of the three proposition omitted or suppressed. A deductive argument with one of its propositions thus missing is called an enthymeme (from a combination of Greek words signifying “in the mind”). As already intimated, the missing proposition may be the major premise, the minor premise, or the conclusion. In every instance the one to whom the argument is addressed is supposed to supply the missing proposition. Let us suppose that someone presents the argument “X would make an ideal candidate for president because he was born in a log cabin.” It is evident after a moment’s analysis that we have here the minor premise and the conclusion of a syllogism. The major premise, which is “All who were born in log cabins make ideal candidates for president,” has been withheld.“Every American is pledged to do his duty, and you are an American” is another form of the enthymeme. Here it is the conclusion “You are Pledged to do your duty” which is withheld. In the enthymeme “All property owners should vote for the bond issue; you should vote for the bond issue” it is the minor premise which must supplied.

Since a great many of the world’s arguments appear in the form of enthymemes, it is of great value to acquire some facility in expanding the enthymeme into a complete syllogism. They, whether or not we shall be persuaded by the argument will depend upon whether or not we accept both of the premises. And even if we can accept both of the premises, we must be able to see whether the conclusion emerges in accordance with the formal rules of the syllogism.

The missing proposition of an enthymeme is sometimes suppressed because the maker of the argument knows that if we look carefully at his premises, we may question or reject one of them. He wishes to sneak his suppressed premise by unnoticed. It is not unfair to say that a large fraction of advertising is presented in the form of enthymemes for just this purpose, and the student of logic will find it a valuable exercise to go through the pages of any popular magazine and determine the suppressed premise in the texts of advertisements. The same may be said of a considerable part of political argumentation, and even of those arguments heard from supposedly non-partisan sources. It is a good rule always to stay on the alert to see on what the maker of an argument is really basing his case.

Still, all enthymemes are not offered with the object of deceiving or imposing upon the unwary. Many enthymemic arguments are perfectly frank and honest, the maker feeling that the unstated premise is too obvious or too generally accepted to require stating. It is ‘in the mind’ of everyone he is addressing.

So, the main idea is this: as you research your policy controversy, the experts are not going to spell out all their premises (because "a great many of the world's arguments come to us in the form of enthymemes"). In order to do an in-depth analysis of the controversy you're going to need to identify some of the premises that are left unstated (underlying assumptions). An exercise would be helpful at this point, right?

Click here for a worksheet you can print out and use to expand some enthymemes into complete syllogisms. The worksheet is not graded. It's just to help you learn to identify assumptions.

For this very reason the enthymeme has been called since ancient times the rhetorical syllogism. This expression requires a little interpretation, but an understanding of it is essential to the remainder of what we have to say about argumentation.



To understand the full scope of argumentation, we must make a distinction between convincingand persuading. Although these words are often used interchangeably in ordinary speech, the student of rhetoric recognizes that to convince is not always to persuade. The term convince has a narrower meaning; it signifies forcing someone to accept a conclusion through the processes of valid argument. If people were changed in their attitudes and actions by being made to grasp the lines of an argument, the world might be a very different place, and we would no longer doubt whether or not man is a rational animal. But in truth the world is not governed by the syllogism, and everyone has witnessed the wisdom of the lines

A man convinced against his will
Is of the same opinion still.

We must not, of course, illogically jump from this to the conclusion that logic is useless. Logic is indispensable, but it will not accomplish everything. It has to be supplemented in most instances by an art to which the name “rhetoric” is sometimes specially applied. This art influences that part of our being not won over by pure reasoning. Although there have been many highly rhetorical discourses which were notable for their bad logic, rhetoric itself is not illogical. As Francis Bacon pointed out, rhetoric no more teaches men to make the worse appear the better cause than logic teaches them to reason fallaciously. Rhetoric is a means of persuasion which takes up where logic ends. After logic has convinced the mind, rhetoric wins the full assent. Therefore in looking at rhetoric, we turn our attention to what one does after making his logical argument.

First, however, we must pursue this distinction further by saying something about the difference between truth and validity. Most authorities on logic use the terms “valid” and “invalid” to indicate whether or not an argument is correct in form. It is essential to understand that these terms apply to the argument as a whole and not to its single propositions. A single proposition is true or false; an argument is valid or invalid. This is so simply because “valid” and “invalid” have references to form, and not to some kind of correspondence with reality, as do “true” and “false.” It is perfectly possible, therefore, to frame a valid syllogism having one or more false propositions. The only test of validity is correctness of form, as we saw in our study of the rules for deductive arguments. Consider for example the following syllogism:

  • All animals are carnivorous.
  • The cow is an animal.
  • Therefore the cow is carnivorous.

Everyone knows that the major premise of this argument is false; nevertheless, if we accept the premise, the conclusion necessarily follows, and this is all that is required to make a valid syllogism. The purely formal nature of valid deductive argument can be seen strikingly if we make a syllogism with nonsense terms, such as the one below.

  • All arps are frimps.
  • All frimps are wackles.
  • Therefore all arps are wackles.

Or we can take a syllogism which consists of notation in the form of symbols.

  • All S is M.
  • All M is P.
  • All S is P.

Now it will be granted that these three arguments “convince” through their formal validity, but they do not persuade in the sense in which we are employing this term. We assent indifferently to the proposition “All S is P” because it does not refer to anything outside its system of symbolization. But as soon as we substitute for the symbols terms which have referents in the real world, our attitude changes. Suppose our syllogism now reads

  • All men are mortal.
  • The President is a man.
  • Therefore the President is mortal.

This argument not only convinces us; it also persuades us, which is to say, it affects our attitude, or it initiates a course of action. In this case, it might be pointed out, one of the courses of action is to maintain the office of vice president. What has entered the argument to make this difference? The new factor is a statement about the world which we accept or reject according to our conception of what is true. Our interest is shifted here to the material truth of a proposition. We no longer ask merely “Is it in proper form?”; we ask also “Is it instantial?” which is to say, “Is it an instance of something factually true?’ The syllogism thus contains not only a valid structure of argument, but also an assertion about the world of reality which has some effect upon our impulse or action. This is where rhetoric appears to supplement logic. Logic addresses itself to the mind; rhetoric addresses itself to the total being, which includes the will. Man is not merely a thinking machine, which is why it is seldom if ever sufficient to give him a conclusion punched out in a machine-like operation. Consequently a complete argument, in addition to obeying the laws of thought, must embody something that we recognize as true about existence. We will be swayed by the argument according to our estimate of the truth of the assertion.

Our next step, therefore, is to discuss where the rhetorical impulse of any argument is to be sought. If our argument is to have more persuasive power than “All arps are wackles,” then a true or probably true perception about the world as we know it must be present.

Now as we return to our syllogism which has real terms and read it searchingly for the kind of predication that it makes about the world, we see that the middle term “man” relates the minor term “President” to the major term “mortal beings.” Thus the argument runs that if the President belongs in the class “man” and if all men belong in the class “mortal beings,” then the President too belongs in the class “mortal beings.” In other words, the President has the generic attribute “mortal being.” In this way the argument depends for its rhetorical force upon the acceptance of the class “mortal beings” as a class having a certain attribute (in this case the certainty of death) which can be ascribed distributively to every member of the class.


If this approach seems to leave some questions unanswered, let us go back to a more fundamental position and think for a moment about the types of assertions we make. We soon become aware that all our assertions reflect our interpretation of the phenomena of existence, and that this interpretation is expressed through certain ultimate conceptions. The most basic of these are, in the language of philosophy, being, cause, and relationship; but we need to translate these terms into language more suited to our purpose. Accordingly, in our everyday assertions we say that a thing exists as a member of a class, or that it is the known cause of a certain effect or the known effect of a certain cause, or that it has points of resemblance with some other thing. “All Democrats are friends of the people” is an assertion of the first type; “War is a cause of inflation” is one of the second, and “Life is like a voyage” is one of the third. These statements about the nature of things enter into arguments (or, strictly speaking, into propositions) and it is the forcefulness with which they impress us that supplies the rhetorical effectiveness of any argument.

Let us restate this from another point of view. It is never enough to have merely a device of argument. A device is only a form, and though forms may delight the intellect, they are seldom if ever sufficient to move that refractory object which is our total being. The total being is moved, if at all, but the content of the argument, and it is content alone with which we are now dealing.

The first writer to give due recognition to content in addition to form was Aristotle, the founder of logic and the author of a treatise on rhetoric. He conceived the content of argument as a group of sources or “topics.” It sheds some light upon this terminology to know that “topics” comes from the Greek word topoi, which signifies “regions” or “places” (cf. topography). The connection becomes clearer when we understand that the “topics” are comprised of those regions of experience from which the propositions of argument can be drawn. We have emphasized the fact that our propositions in argument consist of assertions which reflect our reading of experience. They must say things that we know to be true according to these necessary ways of knowing our world. In proportion as we make the propositions seem truthful, we give an argument power to impel the hearer.

No useful end would be served by going over Aristotle’s list of topics minutely, for there is doubt as to whether he arranged them systematically. Moreover, the topics are not a matter which should be settled by appeal to authority, since we ourselves are qualified judges of the kinds of assertions that move people to acceptance. But taking up the list selectively, we find that the following topics or kinds of statements are the ones most widely understood and most effective in persuading.

  1. Genus or definition
  2. Cause and effect
  3. Circumstance
  4. Similitude
  5. Comparison
  6. Contraries
  7. Testimony
  8. Authority


Genus or Definition

Our first example, involving “mortal beings,” was an instance of the topic genus, which consists of all arguments made from the nature of a thing. It depends for its force upon the principle that there are fixed classes, and that what is true of a class may be imputed to every member of that class. In other words, any object will have the generic attributes of the class to which it belongs. Accordingly, if there is a genus “mortal beings,” and if “man” is a member of this genus, then man will have the attribute of mortality. The language is which the theory of this source of argument has been presented should not obscure the fact that genus is an exceedingly common source. Every time we hear a proposition such as “All Irishmen are brave” or “No politicians are honest” or “Some novels are romances,” we are encountering the topic genus, through which one object or class of objects is given, or denied, the attributes of another class.

For example, a teacher of French says to his class: “In writing French, never omit the accent marks. To a Frenchman accent marks are part of spelling.” This is an argument from definition clearly because accent marks have been defined as a part of spelling. To omit them therefore is the same as to leave something misspelled. This argument also implies a consequence, as do most arguments from definition. But as far as it goes, it says simply that the proper use of accent marks is one with correct spelling. Thus an argument for using French accent marks finds its support in a definition.

It may be helpful to recognize this source of argument in an historical context. Abraham Lincoln in many of his speeches against the spread of slavery put his case in the form of an argument from genus. In a speech made on October 16, 1854, for example, he reasoned as follows:

But if the Negro is a man, is it not to that extent a total destruction of self-government to say that he shall not govern himself? When the white man governs himself, that is self-government; but when he governs himself and also governs another man, that is more than self-government – that is despotism. If the Negro is a man, why then my ancient faith teaches me that ‘all men are created equal,’ and that there can be no moral right in connection with one man’s making a slave of another.

In this utterance it is clearly seen that Lincoln is employing “man” as a genus; that is to say, he is putting “man” in the same place in the argument in which we found “mortal beings” in the argument of our illustration. Now if it is conceded that the Negro belongs to the genus man, it has to be conceded that he has the attributes of manhood, one of which is the right to self-government. In brief, Lincoln is insisting that the attributes of the genus apply distributively to every member of the genus, and this is the rhetorical force of his argument.

So how can you use this knowledge in your speech?

If, when you identify an assumption, you recognize that the assumption is based on an argument from definition, and you disagree with that definition, that recognition should suggest to you the proper way to refute the argument. The argument from cause and effect is discussed next, and will provide a good illustration of the point I'm making here . . .

It is necessary to understand that the success of this rhetoric depends upon a common acknowledgement of the genus “man.” If there is no common conviction that there is such a fixed genus, about which a definite set of predications can be made, then the argument must fail to exert rhetorical force. This fact will explain why many arguments contain lengthy definitions of their terms. Such definitions are nothing more than attempts to fix the genera which are to be used as terms in syllogistic reasoning. In the examples we have been studying, the genera are well established and accepted, and therefore there is little point in defining them. Obviously in most situations it would be needless or even absurd to define “man” or “mortal being.” But there are many genera whose attributes have never been carefully analyzed, and there are others which have been employed so much by pressure groups that the prevailing conception of them is a distorted one. When one is using a genus of this kind, one has no choice but to define or to redefine what he conceives it to be. When John Stuart Mill wrote his classic essay entitled “On Liberty,” he wished to establish certain conclusions about the liberty to which every individual is entitled. But realizing that the term itself has been so variously used by philosophers and by political partisans, he felt compelled to give a lengthy definition of it. Only after that definition was fixed could he use “liberty” in his argument with some hope of persuading people to agree with his conclusion.

The necessity of extended definition of a key term may be illustrated from contemporary usage. It would be a usual thing to hear someone observe, “This is the right course because this is the course of liberalism.” The argument as it stands is an enthymeme, which could be expanded as follows:

  • All courses of liberalism are right courses.
  • This is a course of liberalism.
  • Therefore this is a right course.

Now this argument will carry persuasive force if we know what liberalism is, and if we are for it. If we do not know what it is, naturally we cannot be for it, and in that case the argument would have no rhetorical impulsion. Therefore a minimum need would be to define liberalism, and since this word has suffered greatly from careless and partisan usage, we should take some pains with the definition. The same is at present true of the word “democracy,” despite some supposition that it is a universally understood term. It has been used to describe not only divergent but even contrary political conditions. If one used the word without defining it, one might find it creating an impulse quite different from what was intended.

Arguments from genus and from definition are the same in essence, since both of them are arguments from the nature of a thing, or from an established classification. In the case of the former, the classification is already established, or it is one of the fixed concepts in the mind of the audience to which the argument is addressed. In the case of the second, the work of establishing the classification must be done in the course of the argument, after which the defined term will be used as would any genus.

Arguments based on example belong to this group because an example always implies a general class. A genus must be involved because that is what the example is used to exemplify. It is the first step in an induction which, if carried out, would produce a generalization. When a speaker dwells on the fate of Napoleon at Waterloo, he is saying in effect: here is an instance of the truth that ambitious military conquerors finally overreach themselves and meet disaster. He may play up details of the event to make the instance vivid, but the force of the argument lies in the general proposition about military conquerors, which the example suggests.


Cause and Effect

The topic which depends on cause-and-effect relationship makes use of causal reasoning. It affirms that a given cause implies an effect of proportionate gravity, or that a given effect implies a cause of proportionate gravity. Accordingly, if there is a serious cause, we shall find ourselves in serious plight; if we are now in serious plight, there must exist a serious cause. Let us look at this topic as it might appear in the syllogism.

  • Extravagance produces want.
  • This is a case of extravagance.
  • This is a case which will produce want.

The rhetorical force of the argument depends upon our acceptance of the truth of the cause-and-effect relationship which is affirmed in the major premise. If we grant that extravagance always has, as one of its effects, want, we may be moved to avoid extravagance by our understanding of this relationship. In this way our perception of the causal linkages of phenomena enters into a syllogism as part of its content.

Again let us study the topic in a historical context. When the framers of the Declaration of Independence sat down to produce a persuasive argument for the separation of the American colonies from Great Britain, they relied chiefly upon the argument from effect. The effect was the “facts” which were to be submitted to a candid world. Under seventeen heads the framers listed a large number of particulars in which the colonies had suffered by the policy of the king of Great Britain. Most of us will recall the general tenor if not the content of these. “He has refused his assent to laws, the most wholesome and necessary for the public good….He has dissolved representative Houses repeatedly, for opposing with manly firmness his invasions on the rights of the people….” and so on. Now all of these abuses are pointed out as grave effects which indicate a grave cause, and the cause was seen as a desire to reduce the people of the colonies under an absolute despotism. The colonists were determined that the grave cause should be followed by a different effect, which was to be their separation from the oppressive government of George III. But as far as the rhetorical effect of the argument goes, it is enough to recognize that the proposition asserts a relationship between the suppression of local rights and liberties and despotic rule. Insofar as we are impressed by the truth of that relationship, we will feel a persuasive force in the argument. Enough has been said to show that the argument beginning with cause and moving to effect operates in the same way; if grievous causes exist, grievous effects must follow.

The application to your Persuasive speech of this knowledge should be really clear. Have you ever heard someone assert a bogus causal relationship?  How about this statement:

That kid did something heinous after listening to Ozzy Osbourne music, therefore, it was the music that caused the heinous act.

What is the problem with that claim?  Right!  It doesn't take much reflection to realize that there were probably other factors invovled in the person's heinous act, and, though there may well be a correlation between the behavior and the taste in music, it is a stretch, a fallacy, to assert a cause and effect relationship between the two.  Does this make sense to you?


So, how do I use this information?


You don't really need this knowledge to do the Analysis of Controversy speech, because you're not supposed to make your position known in this assignment; simply analyze, in an even-handed, objective way, both sides of the policy controversy.  However, when it is time to start building your case for your Persuasive speech, you'll need to refute the key arguments on the side with which you disagree.  That's where fallacies come in.  The fallacy that has to do with asserting a bogus causal relationship is called a "post hoc" fallacy.  . . . But we'll get into that later!


A kind of subvariety of the topic cause is the topic circumstance. The argument from circumstance is well summed up in the expression we sometimes hear, “There is nothing else to do about it.” If the situation is such that the facts dictate one course of action, even though that course cannot be vindicated by principle and even though its effect can not be demonstrated, then we are driven back upon the argument from circumstance. We may state its pattern thus: the situation being what it is, there exists no alternative to the action that I recommend. The classic example of the argument from circumstance is Hannibal’s address to his troops upon entering Italy.

You are hemmed in on the right and left by two seas, and you do not have so much as a single ship upon either of them. Then there is the Po before you and the Alps behind. The Po is a deeper, and a more rapid and turbulent river than the Rhone; and as for the Alps, it was with the utmost difficulty that you passed over them when you were in full strength and vigor; they are an insurmountable wall to you now. You are therefore shut in, like our prisoners, on every side, and have no hope of life and liberty but in battle and victory.

In this famous speech, all emphasis is placed upon the coercive nature of the circumstances of the Carthaginian army. This is why we say that it is a simple appeal to circumstances for rhetorical motivation.

But sometimes the argument from circumstances appears in more complex situations. Edmund Burke’s famous speech on conciliation with the colonies is filled with appeals to this source. Indeed, the central point of the speech may be called an argument from circumstance, for Burke was saying to Parliament: since the American colonies are so strong now, and have such a mighty potential for the future, and are so far removed from us, what are you going to do except make peace with them through concessions? The statement often quoted from this speech, “I do not know the method of drawing up an indictment against a whole people,” is again purely an argument from circumstance, because it maintains that the circumstance of the offenders’ being a whole people overshadows the normal course of the law. But the source is seen in its clearest aspect when Burke, after reviewing the fierce spirit of the colonists, declares: “The question is not, whether this spirit deserves praise or blame, but – what, in the name of God, shall we do with it?”

Circumstance belongs to the order of causal relations, but it is the least perceptive, or one might say the least philosophical of the topics. It admits a kind of helplessness in the hands of circumstance – an inability to demonstrate relationships other than the presence of overpowering fact. We recognize this appeal in many advertising and political slogans. The statement that the popular swing is to this kind of cigarette or that kind of automobile, or that 85% of the people buy this kind of breakfast food, or that you should vote for candidate X because he is sure to win, are all slightly disguised arguments from circumstance. Of course these appeals are sometimes supplemented by other arguments, but as far as they themselves go, they utilize only the circumstance of popularity.



The argument from similitude derives its force from a statement about the likeness of two things. To understand how it persuades, we must recall what was said about analogy in our discussion of the devices of logic. We saw that all analogy depends upon a theory that if two things resemble in a certain number of respects, it is probable that they resemble in still further respects. When we argue from similitude, what the major premise does is assert this principle of similarity or comparability. The minor premise then asserts the fact of the similarity and the conclusion asserts the probability of still further similarity. The process may be best seen in the form of a hypothetical syllogism:

  • If S resembles P in X particulars, it is probable that S resembles P in one or more further particulars.
  • S does resemble P in X particulars.
  • Therefore it is probable that S resembles P in one or more further particulars.

As we learned when we examined the theory of analogy, the weight of this probability will depend upon the number and the pertinence of the particulars in which the two instances resemble. Here again we have to observe that the rhetoric of the argument is in direct relation to the soundness of the predication about the world. If the analogy is weak, the argument will have little power to persuade; but if it is strong, the power will be proportionately great.

So, if you recognize an analogy resting at the heart of an argument, and you believe the analogy is bogus (or, a fallacy of "faulty analogy,") it is "like comparing apples to oranges," as we commonly exclaim, how will you refute it?  Easy.  Just start listing the ways in which the comparison breaks down.  Point out dissimilarities in the simile!  Demonstrate, through the power of rhetoric, how the argument doesn't "hold water," so to speak.  Every dissimilarity you can point out is another hole in the leaky bucket. 

So, knowledge of the topics is important in two ways:  it helps one build arguments and it helps one pick apart arguments.  A true artist must be familiar with all the colors on his or her palette.  The topics can be used to craft arugments that get to the heart of the matter and give the audience a variety of approaches (analogy, causation, comparison, etc.) to the issue at hand.  This is the "techne" or technical application of topics; it is how they are used for building arguments.  They are also useful for tearing apart opposing arguments.

Once you identify an assumption, then identify the TYPE of assumption being made, you should have a pretty good idea how to approach the refutation of arguments that you consider bogus.  The reason I'm exposing you to this information now is that, though you won't use it for awhile, you will benefit by knowing the types of assumptions you identify as you are analyzing the heart of the controversial issue you're researching.  When you get around to the refutation in your Persuasive speech, you should really understand how to "attack" the opposing view.  Or, as Weaver puts it, on p. 146, "In studying any extended piece of argumentation for its effect, you will find it invaluable to identify the rhetorical sources being employed.  In no other way can you determine how much content an argument really has and how much weight it is probably going to carry with a specific audience."


Although their names resemble each other, the topic comparison differs somewhat from the topic similitude. Comparison involves a relationship which is sometimes expressed by the Latin phrase a fortiori (“all the stronger”). This argument sets up two possibilities, the second of which is more probable than the first, so that if we affirm the first, we can affirm the second with even greater force, or a fortiori. Using this source of argument, we might say, “If a man will steal from his friend, he will steal from a stranger.” When we look at this assertion analytically, we find we are saying that if a certain man, Richard Roe, belongs to that class of men who will steal from their friends, he is at the same time included, and with greater certainty, in that class of men who will steal from strangers. An excellent example of the argument from comparison is the line from Chaucer:“If gold rusts, what shall iron do?” Here the relationship may be expressed as follows: in a situation where gold will rust, it is much more to be expected that iron will rust. Although the explanation of this source of argument is perhaps not as simple as that of the preceding ones, it will be noted that the source is often employed in actual controversy, e.g., “If even honest men are corrupted by office, what can you expect of crooks?”


The last of the group of sources based on the concept of relationship is that of contraries. The argument from contraries implies that if we are benefiting from a certain fact or situation, then the contrary of the fact or situation will injure us; or, if we are being injured by the situation now existing, we can expect to be benefited by a situation contrary to it. In other words, my present failure or dissatisfaction implies the desirability of the contrary of what I now have; e.g., if we are suffering from war, what we need is peace. If Russia is pleased with the result of our policy in Asia, then what we need is a policy contrary to our present one, and so on.

One of the most interesting examples of the argument from contraries may be found in the “back to nature” movement of the eighteenth century. In this period there developed a highly formal culture, and a number of its prominent thinkers believed that it was suffering from too much formalism. In consequence, there appeared many pleas for a return to a more primitive or natural mode of life, together with admiration for people like the American Indians, who were thought to be unspoiled by civilization. Analysis shows that the “back to nature” movement rested on the following argument: if what we are suffering from is too much artificiality, then what we need is a return to the natural; or, if civilization is the source of our distresses, then we can expect to be benefited by its contrary. This produced an idealization of the primitive, and a desire to recapture the simple and unaffected life such as one encounters in the poetry of Wordsworth.

Testimony and Authority

All of the sources we have analyzed thus far are “internal” in the sense that they involve our own interpretation of experience. But there are two “external” sources, which utilize the interpretation of others. These are testimony and authority. The difference is that whereas the internal source, such as genus or cause, is a direct perception by us of an aspect of phenomena, the external source is a report of such perception on the part of someone else. If a police officer declares in court that he saw you drive through a red light at the intersection of 16th and Walnut, the court accepts his statement as testimony. After this is done, the statement goes into a syllogistic argument as a true proposition, constituting one of the premises. The point we must emphasize is that the proposition, as used in the argument, does not rest upon direct interpretation of genus, or cause, or similitude, but upon the credit of someone who is testifying. In the same way, a man who is charged with a crime gets someone to testify that he was otherwise occupied at the time the crime was committed (this is the true meaning of the charged person’s alibi, which is the Latin word for “elsewhere”). By this means, statements by people presumed to be in a position to know are brought into an argument and take the place of direct of logical interpretation of evidence.

Let us bear in mind that such arguments are external in the sense of being imported from the outside. Instead of affirming a fact of relationship themselves, they affirm that someone else affirms it. Thus the argument would not say that Tony Moreno was seventeen miles away from the scene at the time of a gangland slaying on Chicago’s south side. It says rather that his friend Joe Mangione testifies that Moreno was at his place, which is seventeen miles away from the scene, at the time of the slaying. How good this testimony is must be judged with reference to a number of things. The point of interest to us is that, in estimating its rhetorical force, we regard it not as a fact but as testimony.

Closely related to testimony is authority. Arguments from authority bring in a great name or some other exalted source whose word on the subject in question is regarded as final. Such arguments reflect a supposition that it would be presumptuous to go beyond the authority. The foreign missionary work carried on by many Christian churches rests upon the conclusion of an argument drawn from authority. According to the book of Matthew, Christ said to his disciples (28:19): “Go ye therefore and teach all nations.” The argument then proceeds; if Christ commanded his disciples to spread the gospel to all the world, this is what his followers must do. The Biblical text is thus used to supply a middle term, the authority of Christ, which functions in a syllogistic argument.

All of us have encountered, and perhaps some of us have used, arguments based on the authority of the Bible. If St. Paul said that the greatest of gifts is charity, we must accept this as so. Solomon declared that where there is no vision, the people perish, and we use this as a premise in argument. Arguments from authority are sometimes employed in the political arena. When Washington’s statement that we should avoid entangling alliances with foreign countries is cited in debate over foreign policy, it is the authority of Washington as father and first president of our nation which furnishes the rhetorical force. Sometimes even the subject matter of science is expressed in the form of arguments from authority, since it is obviously impossible to re-investigate every one of the established laws of science every time we wish to make a predication in this field. What we do, therefore, is accept a law on the authority of some competent scientist. When, for example, H. H. Newman, Professor of Zoology at the University of Chicago, declares: “Evolution has been tried and tested in every conceivable way for considerably over half a century. Vast numbers of biological facts have been examined in the light of this principle and without a single exception they have been found entirely compatible with it,” the average layman is disposed to regard this as true. Again we note that it is the authority of the source rather than any direct investigation of the content which gives propositions of this sort a standing in argument.

We repeat that it is the nature of arguments based on testimony and authority to have no intrinsic force; whatever persuasive power they carry is derived from the credit of the testifier of the weight of the authority. People who have been taught to venerate the Bible will be moved by a Biblical proposition; a proposition from the Koran would have little if any power to move them, though it would carry weight with a Moslem. In using such arguments it is accordingly essential to keep in mind the credit of the source of testimony and the status of the authority. Testimony is usually well regarded if the one offering it is in a position to know the facts and if he is disinterested with reference to the outcome of the argument.

In studying any extended piece of argumentation for its effect, you will find it invaluable to identify the rhetorical sources being employed. In no other way can you determine how much content an argument really has and how much weight it is probably going to carry with a specific audience.