In propositional logic, affirming the consequent, sometimes called converse error, fallacy of the converse, or confusion of necessity and sufficiency, is a formal fallacy of taking a true conditional statement under certain assumptions, and invalidly inferring its converse, even though that statement may not be true under the same assumptions. This arises when the consequent has other possible antecedents.
Ad hominem, short for argumentum ad hominem, refers to several types of arguments, most of which are fallacious. Typically this term refers to a rhetorical strategy where the speaker attacks the character, motive, or some other attribute of the person making an argument rather than attacking the substance of the argument itself. This avoids genuine debate by creating a personal attack as a diversion often using a totally irrelevant, but often highly charged attribute of the opponent's character or background. The most common form of this fallacy is "A" makes a claim of "fact," to which "B" asserts that "A" has a personal trait, quality or physical attribute that is repugnant thereby going entirely off-topic, and hence "B" concludes that "A" has their "fact" wrong -without ever addressing the point of the debate.
Fallacies of definition are the various ways in which definitions can fail to explain terms. The phrase is used to suggest an analogy with an informal fallacy. Definitions may fail to have merit, because they: are overly broad, use obscure or ambiguous language, or contain circular reasoning; those are called fallacies of definition. Three major fallacies are: overly broad, overly narrow, and mutually exclusive definitions, a fourth is: incomprehensible definitions, and one of the most common is circular definitions.
A slippery slope fallacy (SSF), in logic, critical thinking, political rhetoric, and caselaw, is a fallacious argument in which a party asserts that a relatively small first step leads to a chain of related events culminating in some significant effect. The core of the slippery slope argument is that a specific decision under debate is likely to result in unintended consequences. The strength of such an argument depends on whether the small step really is likely to lead to the effect. This is quantified in terms of what is known as the warrant. This type of argument is sometimes used as a form of fearmongering in which the probable consequences of a given action are exaggerated in an attempt to scare the audience.
A fallacy, also known as paralogia in modern psychology, is the use of invalid or otherwise faulty reasoning in the construction of an argument that may appear to be well-reasoned if unnoticed. The term was introduced in the Western intellectual tradition by the Aristotelian De Sophisticis Elenchis.
Argument from fallacy is the formal fallacy of analyzing an argument and inferring that, since it contains a fallacy, its conclusion must be false. It is also called argument to logic, the fallacy fallacy, the fallacist's fallacy, and the bad reasons fallacy.
The association fallacy is a formal logical fallacy that asserts that properties of one thing must also be properties of another thing, if both things belong to the same group. For example, a fallacious arguer may claim that "bears are animals, and animals are dangerous; therefore your dog, which is also an animal, must be dangerous."
A thought-terminating cliché is a form of loaded language, often passing as folk wisdom, intended to end an argument and quell cognitive dissonance. Its function is to stop an argument from proceeding further, ending the debate with a cliché rather than a point. Some such clichés are not inherently terminating; they only become so when used to intentionally dismiss dissent or justify fallacious logic.
A complex question, trick question, multiple question, fallacy of presupposition, or plurium interrogationum is a question that has a complex presupposition. The presupposition is a proposition that is presumed to be acceptable to the respondent when the question is asked. The respondent becomes committed to this proposition when they give any direct answer. When a presupposition includes an admission of wrongdoing, it is called a "loaded question" and is a form of entrapment in legal trials or debates. The presupposition is called "complex" if it is a conjunctive proposition, a disjunctive proposition, or a conditional proposition. It could also be another type of proposition that contains some logical connective in a way that makes it have several parts that are component propositions.
Reductio ad Hitlerum, also known as playing the Nazi card, is an attempt to invalidate someone else's argument on the basis that the same idea was promoted or practised by Adolf Hitler or the Nazi Party. Arguments can be termed reductio ad Hitlerum if they are fallacious. Contrarily, straightforward arguments critiquing specifically fascist components of Nazism like Führerprinzip are not part of the association fallacy.
Tu quoque is a discussion technique that intends to discredit the opponent's argument by attacking the opponent's own personal behavior and actions as being inconsistent with their argument, therefore accusing hypocrisy. This specious reasoning is a special type of ad hominem attack. The Oxford English Dictionary cites John Cooke's 1614 stage play The Cittie Gallant as the earliest known use of the term in the English language.
The nirvana fallacy is the informal fallacy of comparing actual things with unrealistic, idealized alternatives. It can also refer to the tendency to assume there is a perfect solution to a particular problem. A closely related concept is the "perfect solution fallacy".
Informal fallacies are a type of incorrect argument in natural language. The source of the error is not just due to the form of the argument, as is the case for formal fallacies, but can also be due to their content and context. Fallacies, despite being incorrect, usually appear to be correct and thereby can seduce people into accepting and using them. These misleading appearances are often connected to various aspects of natural language, such as ambiguous or vague expressions, or the assumption of implicit premises instead of making them explicit.
In logic and philosophy, a formal fallacy, deductive fallacy, logical fallacy or non sequitur is a pattern of reasoning rendered invalid by a flaw in its logical structure that can neatly be expressed in a standard logic system, for example propositional logic. It is defined as a deductive argument that is invalid. The argument itself could have true premises, but still have a false conclusion. Thus, a formal fallacy is a fallacy where deduction goes wrong, and is no longer a logical process. This may not affect the truth of the conclusion, since validity and truth are separate in formal logic.
Appeal to the stone, also known as argumentum ad lapidem, is a logical fallacy that dismisses an argument as untrue or absurd. The dismissal is made by stating or reiterating that the argument is absurd, without providing further argumentation. This theory is closely tied to proof by assertion due to the lack of evidence behind the statement and its attempt to persuade without providing any evidence.
Flag-waving is a fallacious argument or propaganda technique used to justify an action based on the undue connection to nationalism or patriotism or benefit for an idea, group or country. It is a variant of argumentum ad populum. This fallacy appeals to emotion instead to logic of the audience aiming to manipulate them to win an argument. All ad populum fallacies are based on the presumption that the recipients already have certain beliefs, biases, and prejudices about the issue.
The politician's syllogism, also known as the politician's logic or the politician's fallacy, is a logical fallacy of the form:
- We must do something.
- This is something.
- Therefore, we must do this.
Philosophy of logic is the area of philosophy that studies the scope and nature of logic. It investigates the philosophical problems raised by logic, such as the presuppositions often implicitly at work in theories of logic and in their application. This involves questions about how logic is to be defined and how different logical systems are connected to each other. It includes the study of the nature of the fundamental concepts used by logic and the relation of logic to other disciplines. According to a common characterization, philosophical logic is the part of the philosophy of logic that studies the application of logical methods to philosophical problems, often in the form of extended logical systems like modal logic. But other theorists draw the distinction between the philosophy of logic and philosophical logic differently or not at all. Metalogic is closely related to the philosophy of logic as the discipline investigating the properties of formal logical systems, like consistency and completeness.
In argumentation theory, an argumentum ad populum is a fallacious argument which is based on claiming a truth or affirming something is good because the majority thinks so.
