Informal fallacy in the context of "Fallacies of relevance"

In logic and philosophy, a formal fallacy is a pattern of reasoning with a flaw in its logical structure (the logical relationship between the premises and the conclusion). In other words:

• It is a pattern of reasoning in which the conclusion may not be true even if all the premises are true.
• It is a pattern of reasoning in which the premises do not entail the conclusion.
• It is a pattern of reasoning that is invalid.
• It is a fallacy in which deduction goes wrong, and is no longer a logical process.

A formal fallacy is contrasted with an informal fallacy which may have a valid logical form and yet be unsound because one or more premises are false. A formal fallacy, however, may have a true premise, but a false conclusion. The term 'logical fallacy' is sometimes used in everyday conversation, and refers to a formal fallacy.

Appeal to emotion or argumentum ad passiones (meaning the same in Latin) is an informal fallacy characterized by the manipulation of the recipient's emotions in order to win an argument, especially in the absence of factual evidence. This kind of appeal to emotion is irrelevant to or distracting from the facts of the argument (a so-called "red herring") and encompasses several logical fallacies, including appeal to consequences, appeal to fear, appeal to flattery, appeal to pity, appeal to ridicule, appeal to spite, and wishful thinking.

Appeal to emotion is an application of social psychology. It is only fallacious when the emotions that are elicited are irrelevant to evaluating the truth of the conclusion and serve to distract from rational consideration of relevant premises or information. For instance, if a student says "If I get a failing grade for this paper I will lose my scholarship. It's not plagiarized." the emotions elicited by the first statement are not relevant to establishing whether the paper was plagiarized.

In logic, equivocation ("calling two different things by the same name") is an informal fallacy resulting in the failure to define one's terms, or knowingly and deliberately using words in a different sense than the one the audience will understand.

It is a type of ambiguity that stems from a phrase having two or more distinct meanings, not from the grammar or structure of the sentence.

The fallacy of composition is an informal fallacy that arises when one infers that something is true of the whole from the fact that it is true of some part of the whole. A trivial example might be: "This tire is made of rubber; therefore, the vehicle of which it is a part is also made of rubber." That is fallacious, because vehicles are made with a variety of parts, most of which are not made of rubber. The fallacy of composition can apply even when a fact is true of every proper part of a greater entity, though. A more complicated example might be: "No atoms are alive. Therefore, nothing made of atoms is alive." This is a statement most people would consider incorrect, due to emergence, where the whole possesses properties not present in any of the parts.

The fallacy of composition is related to the fallacy of hasty generalization, in which an unwarranted inference is made from a statement about a sample to a statement about the population from which the sample is drawn. The fallacy of composition is the converse of the fallacy of division.

The fallacy of division is an informal fallacy that occurs when one reasons that something that is true for a whole must also be true of all or some of its parts.

A false dilemma, also referred to as false dichotomy or false binary, is an informal fallacy based on a premise that erroneously limits what options are available. The source of the fallacy lies not in an invalid form of inference but in a false premise. This premise has the form of a disjunctive claim: it asserts that one among a number of alternatives must be true. This disjunction is problematic because it oversimplifies the choice by excluding viable alternatives, presenting the viewer with only two absolute choices when, in fact, there could be many.

False dilemmas often have the form of treating two contraries, which may both be false, as contradictories, of which one is necessarily true. Various inferential schemes are associated with false dilemmas, for example, the constructive dilemma, the destructive dilemma or the disjunctive syllogism. False dilemmas are usually discussed in terms of deductive arguments, but they can also occur as defeasible arguments.

In classical rhetoric and logic, begging the question or assuming the conclusion (Latin: petītiō principiī) is an informal fallacy that occurs when an argument's premises assume the truth of the conclusion. Historically, begging the question refers to a fault in a dialectical argument in which the speaker assumes some premise that has not been demonstrated to be true. In modern usage, it has come to refer to an argument in which the premises assume the conclusion without supporting it. This makes it an example of circular reasoning.

Argument from ignorance (Latin: argumentum ad ignorantiam), or appeal to ignorance, is an informal fallacy where something is claimed to be true or false because of a lack of evidence to the contrary.

The fallacy is committed when one asserts that a proposition is true because it has not yet been proven false or a proposition is false because it has not yet been proven true. If a proposition has not yet been proven true, one is not entitled to conclude, solely on that basis, that it is false, and if a proposition has not yet been proven false, one is not entitled to conclude, solely on that basis, that it is true. Another way of expressing this is that a proposition is true only if proven true, and a proposition is false only if proven false. If no proof is offered (in either direction), then the proposition can be called unproven, undecided, inconclusive, an open problem or a conjecture.