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Recognizing fallacies in practical arguments may be difficult since arguments are often structured using rhetorical patterns that obscure the logical connections between assertions. As we illustrate with various examples, fallacies may also exploit the emotions or intellectual or psychological weaknesses of the interlocutor. Having the capability of recognizing logical fallacies in arguments will hopefully reduce the likelihood of such an occurrence.
A different approach to understanding and classifying fallacies is provided by argumentation theory ; see for instance the van Eemeren, Grootendorst reference below. In this approach, an argument is regarded as an interactive protocol between individuals which attempts to resolve a disputed proposition. The protocol is regulated by certain rules of interaction and violations of these rules are fallacies. Many of the fallacies in the list below are best understood as being fallacies in this sense.
In the strictest sense, a logical fallacy is the incorrect application of a valid logical principle or an application of an nonexistent principle:
This is fallacious. Indeed, there is no logical principle which states
The easiest way to show the above inference is invalid is by using Venn diagrams. In logical parlance, the inference is invalid, since under at least one interpretation of the predicates it is not validity preserving.
Unfortunately, few fallacious arguments are as clear cut as the above example suggests. A great many arguments involve causality, which is certainly not part of formal logic. Others involve psychological ploys such as use of power relationships between proposer and interlocutor, appeals to patriotism and morality, appeals to ego etc., to establish necessary intermediate (explicit or implicit) premises for an argument. Indeed, fallacies very often lay in unstated assumptions or implied premises in arguments that are not always obvious at first glance. One way to obscure a premise is through enthymeme.
We now give a few examples illustrating common errors in reasoning. Note that providing a critique of an argument has no relation to the validity of the conclusion. The conclusion could very well be valid, while the argument itself is unsound. See argument from fallacy.
In the following, we view an argument as a dialogue between a proposer and an interlocutor.
James argues:
This argument claims to prove the death penalty is wrong. This particular argument has the form of a categorical syllogism. Any argument must have premises as well as a conclusion. In this case we need to ask what the premises are, that is the set of assumptions the proposer of the argument can expect the interlocutor to grant. The first assumption is almost true by definition: the death penalty is the killing of a criminal who has been duly convicted under a process of lawThis article is about law in society. For other possible meanings, see law (disambiguation). Law (a loanword from Danish-Norwegian lov , in politics and jurisprudence, is a set of rules of conduct which mandate or proscribe (or both) specified relationshi. The second assumption is less clear as to its meaning. Since the assertion has no quantifiers of any kind, it could mean any one of the following:
The third interpretation for example would be those of individuals who accept the Fifth Commandment under a common interpretation in Judeo-Christian theologyThis article is about the list of religious and moral imperatives. For the 1956 film with Charlton Heston, see The Ten Commandments (1956 movie The Ten Commandments or Decalogue are a list of religious and moral imperatives that feature prominently in Jud. In that interpretation, the above syllogism would then fail to have validated its second premise. James may try to assume that his interlocutor believes every act of killing is wrong; if the interlocutor grants this then the argument is valid. In this case, the interlocutor is essentially conceding the point to James. However, the interlocutor is more likely to believe some acts of killing are not wrong, for instance those carried out in self defense or in legitimate warfare; and in this case James is not much better off than he was before he formulated the argument, since he now has to prove the assertion that the death penalty is not a legimate form of killing, which is a disguised form the original thesis. From the point of view the interlocutor, James commits the logical fallacy of begging the questionBegging the question in modern popular usage, is often used synonymously for raising the question . However the correct, original meaning is quite different: it described a type of logical fallacy in which the evidence given for a proposition contains the.