An informal fallacy is an argument whose stated premises fail to support their proposed conclusion. The deviation in an informal fallacy

Fallacy

In logic and rhetoric, a fallacy is usually an incorrect argumentation in reasoning resulting in a misconception or presumption. By accident or design, fallacies may exploit emotional triggers in the listener or interlocutor , or take advantage of social relationships between people...

 often stems from a flaw in the path of reason

Reason

Reason is a term that refers to the capacity human beings have to make sense of things, to establish and verify facts, and to change or justify practices, institutions, and beliefs. It is closely associated with such characteristically human activities as philosophy, science, language, ...

ing that links the premises to the conclusion. In contrast to a formal fallacy

Formal fallacy

In philosophy, a formal fallacy is a pattern of reasoning that is always wrong. This is due to a flaw in the logical structure of the argument which renders the argument invalid...

, the error has to do with issues of ratiocination

Inference

Inference is the act or process of deriving logical conclusions from premises known or assumed to be true. The conclusion drawn is also called an idiomatic. The laws of valid inference are studied in the field of logic.Human inference Inference is the act or process of deriving logical conclusions...

 manifest in language

Natural language

In the philosophy of language, a natural language is any language which arises in an unpremeditated fashion as the result of the innate facility for language possessed by the human intellect. A natural language is typically used for communication, and may be spoken, signed, or written...

 used to state the propositions; the range of elements that can be symbolized by language is broader than that which the symbolism of formal logic

Mathematical logic

Mathematical logic is a subfield of mathematics with close connections to foundations of mathematics, theoretical computer science and philosophical logic. The field includes both the mathematical study of logic and the applications of formal logic to other areas of mathematics...

 can represent.

Deductive and inductive informal fallacies

Informal fallacies of deductive reasoning

Deductive reasoning

Deductive reasoning, also called deductive logic, is reasoning which constructs or evaluates deductive arguments. Deductive arguments are attempts to show that a conclusion necessarily follows from a set of premises or hypothesis...

 contain a fundamental disconnect between the premises and the conclusion that renders the argument invalid

Validity

In logic, argument is valid if and only if its conclusion is entailed by its premises, a formula is valid if and only if it is true under every interpretation, and an argument form is valid if and only if every argument of that logical form is valid....

. This disconnect often stems from the presence of a hidden co-premise

Co-premise

A co-premise is a premise in reasoning and informal logic which is not the main supporting reason for a contention or a lemma, but is logically necessary to ensure the validity of an argument...

 that, if presented, would validate the argument.

Inductive

Inductive reasoning

Inductive reasoning, also known as induction or inductive logic, is a kind of reasoning that constructs or evaluates propositions that are abstractions of observations. It is commonly construed as a form of reasoning that makes generalizations based on individual instances...

 informal fallacies are slightly different from their deductive counterparts, as their merit rests in the inductive strength

Statistical inference

In statistics, statistical inference is the process of drawing conclusions from data that are subject to random variation, for example, observational errors or sampling variation...

 of the premise-conclusion link rather than in the presence of hidden premises. For instance, the fallacy of hasty generalization

Hasty generalization

Hasty generalization is a logical fallacy of faulty generalization by reaching an inductive generalization based on insufficient evidence essentially making a hasty conclusion without considering all of the variables...

, can be roughly stated as:

p) A is an X

p) A is also a Y

c) therefore, all Xs are also Ys

If the populations X and Y are both too large to sample completely, then the statement is inductive. In such a case, a hasty generalization occurs when the number of Xs and Ys is insufficient to represent the respective populations. It is important to distinguish between a principle of reasoning (deductive or inductive) and the premise of an argument.

See also

• Argumentation theory
  Argumentation theory
  Argumentation theory, or argumentation, is the interdisciplinary study of how humans should, can, and do reach conclusions through logical reasoning, that is, claims based, soundly or not, on premises. It includes the arts and sciences of civil debate, dialogue, conversation, and persuasion...
  
  
• Argument map
• Critical thinking
  Critical thinking
  Critical thinking is the process or method of thinking that questions assumptions. It is a way of deciding whether a claim is true, false, or sometimes true and sometimes false, or partly true and partly false. The origins of critical thinking can be traced in Western thought to the Socratic...
  
  
• Inference objection
  Inference objection
  In informal logic, an inference objection is an objection to an argument based not on any of its stated premises, but rather on the relationship between premise and contention. For a given simple argument, if the assumption is made that its premises are correct, fault may be found in the...
  
  
• Inquiry
  Inquiry
  An inquiry is any process that has the aim of augmenting knowledge, resolving doubt, or solving a problem. A theory of inquiry is an account of the various types of inquiry and a treatment of the ways that each type of inquiry achieves its aim.-Deduction:...
  
  
• Lemma
  Lemma (logic)
  In informal logic and argument mapping, a lemma is simultaneously a contention for premises below it and a premise for a contention above it....
  
  
• Sophism
  Sophism
  Sophism in the modern definition is a specious argument used for deceiving someone. In ancient Greece, sophists were a category of teachers who specialized in using the tools of philosophy and rhetoric for the purpose of teaching aretê — excellence, or virtue — predominantly to young statesmen and...
  
  

External links

• Logical fallacies A list of logical fallacies, explained.
• An Informal Fallacy Primer
• The Fallacy Files: Informal Fallacy
• Appeal to Authority Appeal to Authority Logical Fallacy