by Scott F. Aikin and Robert B. Talisse
Formal fallacies are pervasive errors of formal inferences. Consider the argument:
If Bill is a carpenter, then Bill is handy.
Bill is handy.
Therefore, Bill is a carpenter.
This argument fails because the truth of the premises does not guarantee the truth of the conclusion: the first premise states that being a carpenter is sufficient for being handy; it does not claim that all and only handy people are carpenters. After all, Bill could be a handy car mechanic who has never cut a piece of wood. We call this error the fallacy of affirming the consequent. This error gets its own name because we are especially prone to this kind of mistake. Once one is trained to spot it, one will find that this fallacy is committed frequently.
By contrast, informal fallacies are pervasive errors in informalinferences. Informal inferences differ from formal ones in that the latter propose to demonstrate the truth of their conclusions whereas the former aspire only to show that their conclusions are most likely true. A familiar informal fallacy is the ad populum fallacy. Consider:
Most people think that Joe is guilty.
Therefore, Joe is guilty.
This argument fails because it appeals simply to what “most people” think, without any regard for questions concerning the level to which “most people” are informed of the relevant facts of Joe's case. The mere fact that “most people” agree about some claim is no evidence at all for its truth.
The important thing about fallacies is that they are attractive and so pervasive errors of reasoning. Part of what accounts for their popularity is the way in which they mimic or ride piggyback on proper inferences. The fallacy of affirming the consequent is a mimic of the obviously successful inference known as modus ponens:
If Bill is a carpenter, then Bill is handy.
Bill is a carpenter.
Therefore, Bill is handy.
And the ad populum fallacy derives its force from the fact that it is often wise to accept the judgment of a group of people who agree amongst themselves, provided that they are well-informed and reliable judges concerning the matter at hand. Fallacies attract us because to the casual ear they sound a lot like proper argument forms.
So what, then, is a dialectical fallacy? The first thing to note is that both formal and informal fallacies can be perpetrated against oneself or an interlocutor; the standard fallacies are hence first- or second-personal. But arguments often take place publicly, in front of an audience of onlookers. In fact, in a democratic society, arguments concerning matter of great importance are often enacted for the sake of an audience. In these public contexts, those who argue do so not only for the sake of settling a disagreement between them; they argue in large part for the sake of affecting the spectators. The audience then becomes a (mostly) silent third party to the argument, and although the speakers typically do not address onlookers directly, the audience is frequently the target of what is said.
This public feature of argument is significant in many respects. It most obviously is the site for new forms of argument failure, and dialectical fallacies are those attractive and prevalent failures of reasoning that are occasioned by the public setting of an argument. When Alfred argues with Betty for the sake of moving an onlooking audience, he is often not merely concerned with demonstrating to Betty that his view is correct and hers not; he is also concerned to be seen by the audience to be correcting Betty, perhaps even to be teaching her. In other words, Alfred's aim is not simply to have the better argument, but to best Betty in argument.
Much of the grotesque pantomime that passes these days for public political debate on television, radio, and the Internet manifests this structure. The point is not really to win the argument or follow the best reasons, but rather to be seen by an already sympathetic self-selected audience to overcome the opposition. To be sure, one way to build a case for one's view is to rack up wins against its opponents. But notice that, as with the ad populum, developing a strong record of successful argumentative engagements with one's opposition supplies support for one's view only when one has prevailed against the competent, well-informed, and reliable opponents of one's view. In other words, winning arguments against intellectual patsies brings no epistemic credit to one's view. Nonetheless, it is often the case that an audience that is antecedently sympathetic to one's view can be counted on to not know much about the opposition; hence they are likely to be unable to distinguish the patsies from the formidable exponents of the opposing sides.
An especially common dialectical fallacy now comes into clear view. In what we call the weak man fallacy, an argumentative exchange is staged between an advocate of some view and an especially weak proponent of the opposing view. The advocate then makes quick work of the feeble opponent, yet presents herself to the onlookers as having refuted the opposition as such. The fallacy in the weak man consists in the misrepresentation of the dialectical score to the audience. In successful deployments of the weak man fallacy, the sympathetic onlookers are encouraged to think that the advocate of their favored view has bested a competent and well-informed opponent. They hence take themselves to have reason to see their favored view in even better light than before the argument began. In fact, however, the advocate successfully defended the favored view against a version of the oppositions which is, unbeknownst to the audience, flimsy and intellectually unserious. The onlookers have been led to draw a faulty conclusion (the case for the favored view is especially compelling) on the basis of considerations that only mimic aproper inference.
The weak man fallacy is but one instance of the broader category of dialectical fallacies. Several others are examined at length in Why We Argue (And How We Should). The dialectical fallacies are unified by two features. First, they all involve treating one's interlocutor as merely an instrument by which one makes a presentation to an audience of onlookers. Second, they all involve treating the argumentative exchange with an interlocutor as an occasion to manipulate the audience's perception of the dialectical situation that obtains between one's favored view and its opposition. Most frequently, dialectical fallacies involve manipulating one's audience into adopting a fundamentally distorted and highly unfavorable view of one's opponents. Frequently the aim is to encourage among the audience the view that one's opposition is intrinsically foolish, ignorant, incompetent, wicked, treasonous, or worse. After all, it is easy to win support for one's views among those who have been convinced that only the depraved or brainless could oppose them. And this, finally, is one respect in which dialectical fallacies are especially vicious failures of reasoning: In aiming to convince onlookers that one's views cannot be rationally opposed, they are attacks on the very idea of argument.
We have noted elsewhere that, as it is a book about the proper role of reasoning in politics, Why We Argue (And How We Should) has occasioned its share of comical reaction. We admit that there is very little proper reasoning to be found in our current politics. But that's an indictment of our politics, not a proof that we should expect no more than crass pageantry and empty posturing in the political world. In fact, at the core of our democratic ideal is the commitment to the possibility of reasoned self-government amongst citizens who disagree deeply about the most important matters. Reason in politics? In a democracy, you'd better believe it.