Logical Fallacies

Personal attacks

(arguments ad hominem) attempt to discredit a point of view by discrediting the person that holds it. The character of the person that holds a view, though, entails nothing about the truth of that view. Such arguments therefore

logical fallacy

A logical fallacy is, roughly speaking, an error of reasoning. When someone adopts a position, or tries to persuade someone else to adopt a position, based on a bad piece of reasoning, they commit a fallacy.

Straw Man Fallacy

A straw man argument is one that misrepresents a position in order to make it appear weaker than it actually is, refutes this misrepresentation of the position, and then concludes that the real position has been refuted. Example (1) Trinitarianism holds that three equals one. (2) Three does not equal one. Therefore: (3) Trinitarianism is false. This is an example of a straw man argument because its first premise misrepresents trinitarianism, its second premise attacks this misrepresentation of trinitarianism, and its conclusion states that trinitarianism is false. Trinitarianism, of course, does not hold that three equals one, and so this argument demonstrates nothing concerning its truth.

Informal Fallacy (Inductive Fallacies)

An informal fallacy is fallacious because of both its form and its content informal fallacies are errors of reasoning that cannot easily be expressed in our system of formal logic (such as symbolic, deductive, predicate logic).

Formal Fallacies (Deductive Fallacies)

Deductive arguments are supposed to be water-tight. For a deductive argument to be a good one (to be "valid") it must be absolutely impossible for both its premises to be true and its conclusion to be false. The formal fallacies are fallacious only because of their logical form. Any deductive argument that fails to meet this (very high) standard commits a logical error, and so, technically, is fallacious. A formal fallacy occurs when it produces a contradiction within the system of premises. When a system of premises produces a contradiction, the entire system must be rejected, on the basis that a system containing a contradiction will prove the truth of any proposition, including the negation of the propositions granted by the system. A formal fallacy can be detected by examining the logical form of the reasoning, whereas an informal fallacy depends upon the content of the reasoning and possibly the purpose of the reasoning.

Fallacies of Ambiguity

Fallacies of ambiguity appear to support their conclusions only due to their imprecise use of language. Once terms are clarified, fallacies of ambiguity are exposed. It is to avoid fallacies of this type that philosophers often carefully define their terms before launching into an argument. the arguer misinterprets a statement that is syntactically ambiguous and proceeds to draw a conclusion based on this faulty interpretation. The tour guide said that standing in Greenwich Village, the Empire State Building could easily be seen. It follows that the Empire State Building is in Greenwich Village. when the conclusion of an argument depends on the erroneous transference of an attribute from the parts of something onto the whole. equivocation and amphiboly. The accent fallacy, and the fallacy of equivocation, are classic examples of fallacies of ambiguity. Equivocation is particularly important to look out for in evaluating philosophical arguments. Accent, Amphiboly and Equivocation are examples of fallacies of ambiguity.

Fallacies of Presumption

Fallacies of presumption are not errors of reasoning in the sense of logical errors, but are nevertheless commonly classed as fallacies. Fallacies of presumption begin with a false (or at least unwarranted) assumption, and so fail to establish their conclusion. Examples Arguments involving false dilemmas, complex questions, or circularity all commit fallacies of presumption: false dilemmas assume that there are no other options to consider; complex questions assume that a state of affairs holds when it may not; circular arguments assume precisely the thing that they seek to prove. In each case, the assumption is problematic, and prevents the argument from establishing its conclusion. Begging the Question, False Dilemma, No True Scotsman, Complex Question and Suppressed Evidence. begging the question, complex question, false dichotomy, and suppressed evidence.

Fallacies of Relevance informal

Fallacies of relevance are attempts to prove a conclusion by offering considerations that simply don't bear on its truth. In order to prove that a conclusion is true, one must offer evidence that supports it. Arguments that commit fallacies of relevance don't do this; the considerations that they offer in support of their conclusion are irrelevant to determining whether that conclusion is true. Ad Hominem, Appeal to Pity, and Affirming the Consequent are some other fallacies of relevance.

False Dilemma / Bifurcation Fallacy

The bifurcation fallacy is committed when a false dilemma is presented, i.e. when someone is asked to choose between two options when there is at least one other option available. xamples (1) Either a Creator brought the universe into existence, or the universe came into existence out of nothing. (2) The universe didn't come into existence out of nothing (because nothing comes from nothing). Therefore: (3) A Creator brought the universe into existence. Complex questions - are subtle forms of false dilemma. Questions such as "Are you going to admit that you're wrong?" implicitly restrict the options to either being wrong and admitting it or being wrong or not admitting it, thus excluding the option of not being wrong.

Equivocation Fallacy

The fallacy of equivocation is committed when a term is used in two or more different senses within a single argument. when the conclusion of an argument depends on the fact that a word or phrase is used, either explicitly or implicitly invalid or have a false premise ex. Some triangles are obtuse. Whatever is obtuse is ignorant. Therefore, some triangles are ignorant The fallacy of equivocation is committed when a term is used in two or more different senses within a single argument.

Appeals to consequences

attempt to persuade someone to accept a position based either on the good consequences of their accepting it or on the bad consequences of their not accepting it. There is no guarantee, though, that the position that has the best consequences is true. Again, then, such arguments commit a fallacy of relevance.

'No True Scotsman'

fallacy, for example, could be classified either as a fallacy of ambiguity (an attempt to switch definitions of "Scotsman") or as a fallacy of presumption (it begs the question, reinterpreting the evidence to fit its conclusion rather than forming its conclusion on the basis of the evidence).

petitio principii

occurs when the premise of an argument merely restates the conclusion in slightly different language. Examples: Capital punishment is justified for the crimes of murder and kidnapping because it is quite legitimate and appropriate that someone be put to death for having committed such hateful and inhuman acts

complex question

presumes that a question can be answered by a simple ''yes,'' ''no,'' or other brief answer when a more sophisticated answer is needed when a single question that is really two (or more) questions is asked and a single answer is then applied to both questions. ex. Have you stopped cheating on exams? Where did you hide the cookies you stole?

False dichotomy

presumes that an ''either . . . or . . .'' statement presents mutually exhaustive alternatives when in fact it does not ''false bifurcation'' and the ''either or fallacy'') Either you let me attend the Garth Brooks concert or I'll be miserable for the rest of my life. I know you don't want me to be miserable for the rest of my life, so it follows that you'll let me attend the concert.

suppressed evidence

presumes that no important evidence has been overlooked by the premises when in fact it has. Most dogs are friendly and pose no threat to people who pet them. Therefore, it would be safe to pet the little dog that is approaching us now.

Begging the question

presumes that the premises provide adequate support for the conclusion when in fact they do not ex. Murder is morally wrong. This being the case, it follows that abortion is morally wrong. something has been left out of the original arguments