In philosophy

Philosophical logic

Philosophical logic is a term introduced by Bertrand Russell to represent his idea that the workings of natural language and thought can only be adequately represented by an artificial language; essentially it was his formalization program for the natural language...

, 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

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....

. A formal 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...

 is contrasted with an informal fallacy

Informal fallacy

An informal fallacy is an argument whose stated premises fail to support their proposed conclusion. The deviation in an informal fallacy often stems from a flaw in the path of reasoning that links the premises to the conclusion...

, which may have a valid logical form

Logical form

In logic, the logical form of a sentence or set of sentences is the form obtained by abstracting from the subject matter of its content terms or by regarding the content terms as mere placeholders or blanks on a form...

, but be false due to the characteristics of its premise

Premise

Premise can refer to:* Premise, a claim that is a reason for, or an objection against, some other claim as part of an argument...

s, or its justification structure.

The term 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...

is often used generally to mean an argument that is problematic for any reason, whether it is formal or informal.

The presence of a formal fallacy in a deductive argument does not imply anything about the argument's premises or its conclusion. Both may actually be true, or even more probable as a result of the argument, but the deductive argument is still invalid because the conclusion does not follow from the premises in the manner described. By extension, an argument can contain a formal fallacy even if the argument is not a deductive one; for instance an inductive argument that incorrectly applies principles of probability

Probability

Probability is ordinarily used to describe an attitude of mind towards some proposition of whose truth we arenot certain. The proposition of interest is usually of the form "Will a specific event occur?" The attitude of mind is of the form "How certain are we that the event will occur?" The...

 or causality

Causality

Causality is the relationship between an event and a second event , where the second event is understood as a consequence of the first....

 can be said to commit a formal fallacy.

"Fallacious arguments usually have the deceptive appearance of being good arguments." Recognizing fallacies in everyday arguments may be difficult since arguments are often embedded in rhetoric

Rhetoric

Rhetoric is the art of discourse, an art that aims to improve the facility of speakers or writers who attempt to inform, persuade, or motivate particular audiences in specific situations. As a subject of formal study and a productive civic practice, rhetoric has played a central role in the Western...

al patterns that obscure the logical connections between statements. Informal fallacies may also exploit the emotion

Emotion

Emotion is a complex psychophysiological experience of an individual's state of mind as interacting with biochemical and environmental influences. In humans, emotion fundamentally involves "physiological arousal, expressive behaviors, and conscious experience." Emotion is associated with mood,...

al, intellectual, or psychological

Psychology

Psychology is the study of the mind and behavior. Its immediate goal is to understand individuals and groups by both establishing general principles and researching specific cases. For many, the ultimate goal of psychology is to benefit society...

 weaknesses of the audience. Having the capability to recognize fallacies in arguments is one way to reduce the likelihood of such occurrences.

A different approach to understanding and classifying fallacies is provided by 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...

. In this approach, an argument is regarded as an interactive protocol between individuals which attempts to resolve their disagreements. The protocol is regulated by certain rules of interaction and violations of these rules are fallacies.

Such fallacies are used in many forms of modern communications where the intention is to influence behavior and change beliefs. Examples in the mass media

Mass media

Mass media refers collectively to all media technologies which are intended to reach a large audience via mass communication. Broadcast media transmit their information electronically and comprise of television, film and radio, movies, CDs, DVDs and some other gadgets like cameras or video consoles...

 today include but are not limited to propaganda

Propaganda

Propaganda is a form of communication that is aimed at influencing the attitude of a community toward some cause or position so as to benefit oneself or one's group....

, advertisements, politics

Politics

Politics is a process by which groups of people make collective decisions. The term is generally applied to the art or science of running governmental or state affairs, including behavior within civil governments, but also applies to institutions, fields, and special interest groups such as the...

, newspaper editorials and opinion-based news shows.

In contrast to informal fallacy

As modus ponens

Modus ponens

In classical logic, modus ponendo ponens or implication elimination is a valid, simple argument form. It is related to another valid form of argument, modus tollens. Both Modus Ponens and Modus Tollens can be mistakenly used when proving arguments...

, the following argument contains no formal fallacies.

1. If P then Q
2. P
3. Therefore Q

If statements 1 and 2 are true, it will absolutely follow that statement 3 is true. However, it may still be the case that statement 1 or 2 is not true. For example:

1. If a scientist makes a statement about science, it is correct.
2. Albert Einstein
   Albert Einstein
   Albert Einstein was a German-born theoretical physicist who developed the theory of general relativity, effecting a revolution in physics. For this achievement, Einstein is often regarded as the father of modern physics and one of the most prolific intellects in human history...
   
    states that all quantum mechanics is deterministic
   Bohr-Einstein debates
   The Bohr–Einstein debates were a series of public disputes about quantum mechanics between Albert Einstein and Niels Bohr, who were two of its founders. Their debates are remembered because of their importance to the philosophy of science. An account of them has been written by Bohr in an article...
   
   .
3. Therefore it's true that quantum mechanics is deterministic.

In this case, statement 1 is false. The particular informal fallacy being committed in this assertion is argument from authority

Argument from authority

Argument from authority is a special type of inductive argument which often takes the form of a statistical syllogism....

. By contrast, an argument with a formal fallacy could still contain all true premises:

1. If Bill Gates
   Bill Gates
   William Henry "Bill" Gates III is an American business magnate, investor, philanthropist, and author. Gates is the former CEO and current chairman of Microsoft, the software company he founded with Paul Allen...
   
    owns Fort Knox
   Fort Knox
   Fort Knox is a United States Army post in Kentucky south of Louisville and north of Elizabethtown. The base covers parts of Bullitt, Hardin, and Meade counties. It currently holds the Army Human Resources Center of Excellence to include the Army Human Resources Command, United States Army Cadet...
   
   , then he is rich.
2. Bill Gates is rich.
3. Therefore, Bill Gates owns Fort Knox.

Though, 1 and 2 are true statements, 3 does not follow because the argument commits the formal fallacy of affirming the consequent

Affirming the consequent

Affirming the consequent, sometimes called converse error, is a formal fallacy, committed by reasoning in the form:#If P, then Q.#Q.#Therefore, P....

.

An argument could contain both an informal fallacy and a formal fallacy yet have a correct conclusion, for example, again affirming the consequent:

1. If a scientist makes a statement about science, it is correct.
2. It's true that quantum mechanics is deterministic.
3. Therefore a scientist has made a statement about it.

See also

• Apophasis
  Apophasis
  Apophasis refers, in general, to "mention by not mentioning". Apophasis covers a wide variety of figures of speech.-Apophasis:...
  
  
• Cogency
• Cognitive bias
  Cognitive bias
  A cognitive bias is a pattern of deviation in judgment that occurs in particular situations. Implicit in the concept of a "pattern of deviation" is a standard of comparison; this may be the judgment of people outside those particular situations, or may be a set of independently verifiable...
  
  
• Demagogy
  Demagogy
  Demagogy or demagoguery is a strategy for gaining political power by appealing to the prejudices, emotions, fears, vanities and expectations of the public—typically via impassioned rhetoric and propaganda, and often using nationalist, populist or religious themes...
  
  
• 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...
  
  
• False statement
  False statement
  A false statement is a statement that is either willfully or unknowingly untrue. Though the word fallacy is often used as a synonym for false statement, this is not what is meant by "fallacy" in logic or most formal contexts....
  
  
• Informal logic
  Informal logic
  Informal logic, intuitively, refers to the principles of logic and logical thought outside of a formal setting. However, perhaps because of the informal in the title, the precise definition of informal logic is matters of some dispute. Ralph H. Johnson and J...
  
  
• Invalid proof
  Invalid proof
  In mathematics, certain kinds of mistakes in proof, calculation, or derivation are often exhibited, and sometimes collected, as illustrations of the concept of mathematical fallacy...
  
  
• Paradox
  Paradox
  Similar to Circular reasoning, A paradox is a seemingly true statement or group of statements that lead to a contradiction or a situation which seems to defy logic or intuition...
  
  
• 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...
  
  
• Soundness
  Soundness
  In mathematical logic, a logical system has the soundness property if and only if its inference rules prove only formulas that are valid with respect to its semantics. In most cases, this comes down to its rules having the property of preserving truth, but this is not the case in general. The word...
  
  
• Validity
  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....
  
  

External links

• The Fallacy Files by Gary N. Curtis – real examples posted regularly
• ESGE Logical Fallacies – European Society for General Semantics
• Logical Fallacies .Info
• Stephen Downes Guide to the Logical Fallacies
• Marilyn vos Savant explains Logical Fallacies