sbcc Philosophy-111 Critical Thinking And Writing:

Informal Fallacies in Reasoning




Video Intro

Now we take up the study of INFORMAL FALLACIES in reasoning. In our course textbook, REASON ARGUE REFUTE, this material is found on pages 23-33. On page 23 we read;

" Section 3:

Reasoning Fallacies in Three Categories: Irrelevance, Presumption and Ambiguity

Fallacies are failed attempts at reasoning. Part of knowing what successful reasoning is entails knowing what successful reasoning is not. We now take up the study of informal fallacies in the process of reasoning. Reasoning fallacies are not like errors of fact, they are mistakes in the process of thinking. Like some lost traveler, fallacies happen when the mind takes a wrong turn trying to negotiate an inference. You can make an error in trying to balance your checkbook, but it would be improper to accuse you of committing an informal fallacy. However, you can be accused of committing an informal fallacy if, in the act of reasoning, you are vague, ambiguous, careless, presumptive, or allow some unrelated factors to mistakenly divert your premises from a necessary conclusion.

These reasoning mistakes are quite common in every day discourse.  We need not strain hard to find news reports, film ‘documentaries,’ TV commercials, internet ‘blogs’, serious discussions, and debates in public and private life replete with informal fallacies of reasoning.  We are all human and we all commit these mistakes in reasoning though we are slow to admit it, and quick to point it out in others. Critical thinkers and writers, however, constantly develop the necessary self-discipline to both recognize and eliminate these mistakes in their reasoning process."

All 17 informal fallacies of reasoning are the material that will comprise the sole content of Exam #2.

Later in our course we will study FORMAL logical fallacies which are defects in the FORM (structure) of reasoning.  Our study topic now concerns INFORMAL fallacies which are mistakes in the PROCESS of reasoning.

Example of a FORMAL fallacy:
                                                “If I won the Mega Lotto 100 million dollar prize, then I am wealthy.
                                                  I did not win the Mega Lotto 100 million dollar prize.
                                                Therefore, I am not wealthy.”

 (This FORM of reasoning is invalid since I may be wealthy by a host of other means apart from winning the Mega Lotto 100 million dollar prize. The 'form', that is violated is " If p is the case then q is the case. p is not the case. Therefore q is not the case.)

Example of an INFORMAL fallacy:
                                               " Statistics show that The Bible is the most shoplifted book on the planet. Therefore we shouldn't’t object to students plagiarizing copyrighted material for their research papers."

(While this seems to have the structure of a valid argument, the premise is not relevant to the conclusion and thus the reasoning process is broken.)

To fully understand logic, critical thinkers and writers need to distinguish fallacious reasoning from valid and sound reasoning. The study of Informal Fallacies affords us this opportunity. Our text discusses three major categories of fallacies: fallacies of relevance, fallacies of presumption, and fallacies of ambiguity. There are many more informal fallacies than these. The ones we will study are simply the most commonly recognizable.

Informal fallacies are simply MISTAKES IN THE REASONING PROCESS ITSELF. These mistakes are quite common in everyday discourse, news reports, and even in 'serious' discussions and debates in public and private life. We are all human and we all commit these mistakes in reasoning. The critical thinker and writer, however, constantly works at the necessary self-discipline required to both recognize these mistakes in reasoning, and eliminate making judgments based on these INFORMAL FALLACIES.

For good reason, Informal Fallacies fall into three general categories that correspond to the type of DEFECT in the reasoning process encountered.

As the term implies, fallacies of relevance rely on premises which may seem relevant (related), but which in fact are not. Such arguments are fallacies because they distract attention away from relevant facts under inquiry and attempt to prove the truth of their conclusions based on unrelated information.

Fallacies of presumption contain dubious, suspicious or outright false premises in need of factual proof that are simply assumed to be true. You need to be able to see why these assumptions are made, and how to avoid making them, or be taken in by them as they sometimes pass for ‘cogent’ reasoning.

In fallacies of ambiguity, valid reasoning goes wrong because words, phrases or entire propositions with more than one definite meaning in the argument are misleading, and therefore cannot imply the conclusion with logical necessity.

Key Concepts:

A fallacy is an error in reasoning-a type of argument that may seem to be correct, but that proves not to be so upon closer examination. An argument is said to commit a fallacy when it makes a reasoning mistake due to a lack of relevance, unwarranted presumption, and/or language ambiguity. Within these three subcategories, this chapter covers 17 different logical fallacies. Be advised that it often happens that informal fallacies are brewed in 'cocktails' of several fallacies all in the same argument. It is also interesting to note that these informal fallacies are sometimes DELIBERATLY committed in order to coerce, deceive, or mislead others seeking truth.

Fallacies of relevance rely on premises that seem to be relevant to the conclusion when, in fact, they are not. There are seven major fallacies of relevance:

1. Arguments from ignorance (ad ignorantiam i.e. from lack of knowledge)
2. Appeals to inappropriate authority (ad verecundiam i.e. from false authority)
3. Arguments against the person (ad hominem i.e. to the man or person)
4. Appeals to popular emotion (ad populum i.e. from what is popular)
5. Appeals to pity (ad misericordiam i.e. from misery or pity)
6. Appeals to force (ad baculum i.e. to the stick or force)
7. Irrelevant conclusions (ignoratio elenchi i.e. ignorance of the refutation)

Fallacies of presumption arise when an argument relies on a proposition that is assumed to be true, but is in fact false, dubious, or without warrant. There are five such fallacies:

1. Complex question
2. False cause (Post hoc, ergo propter hoc i.e. after this, therefore because of this; also known as Non Sequitur i.e. it does not follow)
3. Begging the question (petitio principii i.e. arguing in a circle)
4. Accident
5. Converse accident

Fallacies of ambiguity occur when arguments are formulated such that they rely on shifts in the meaning of words from their premises to their conclusions. Such ambiguous language results in five fallacies of ambiguity:

1. Equivocation
2. Amphiboly
3. Accent
4. Composition
5. Division

Fallacies of Relevance

In this category of informal fallacies, the mistaken arguments rely on premises that may seem to be relevant to the conclusion, but in fact they are not relevant. Here, we examine these mistakes of reasoning in seven fallacies of relevance. Some are known by their Latin names that you will be responsible to recognize on exams as they have passed into common language usage.

1. Argument from ignorance (ad ignorantiam): When it is argued that a proposition is true on the ground that it has not been proved false, or when it is argued that a proposition is false because it has not been proved true.

Example: Since no one has disproved that ethnic 'diversity' is a sufficient condition for a 'better' learning environment, then it must be the case that ethnic 'diversity' is a sufficient condition for a 'better' learning environment.

2. Appeal to inappropriate authority (ad verecundiam): When the premises of an argument appeal to the judgment of some party or parties having no legitimate claim to authority in the matter at hand.

Example: Sean Penn just returned from Iraq and he says that Saddam Hussein is a great leader of the Iraqi people. That settles it for me. Since I love all Penn's movies, then Saddam must be a great leader of the Iraqi people.

3. Argument against the person (ad hominem): When an attack is leveled not at the claims being made or the merits of the argument, but at the person of the opponent. Arguments ad hominem take two forms. When the attack is directly against persons, seeking to defame or discredit them, it is called an "abusive ad hominem."

Example: The war in Iraq is morally wrong because President Bush is a failed Texas cowboy, frat boy drunk, who committed fraud and bribery to wage it.

When the attack is indirectly against persons, suggesting that they hold their views chiefly because of their special circumstances or interests, it is called a "circumstantial ad hominem."

Example: I find it interesting that all the Senators who voted for drafting 18 year olds into the military are themselves well beyond draft age.

4. Appeal to emotion (ad populum): When careful reasoning is replaced with devices calculated to elicit enthusiasm and emotional support for the conclusion advanced.

Example: "So Bill Clinton lied about having extra-marital sex in the Oval Office of the White house. Cool! Everybody lies about sex."

5. Appeal to pity (ad misericordiam): When careful reasoning is replaced by devices calculated to elicit sympathy on the part of the hearer for the objects of the speaker's concern.

Example: You can't fail me in this course! I NEED this course to transfer to University, and my parents will kill me if I don't transfer this semester.

6. Appeal to force (ad baculum): When careful reasoning is replaced with direct or insinuated threats to bring about the acceptance of some conclusion.

Example: I can assure you that deciding the beneficiaries of my estate will have nothing to do with the amount of love and affection people showed to me during my lifetime.

7. Irrelevant conclusion (ignoratio elenchi): When the premises miss the point, purporting to support one conclusion while in fact supporting or establishing another.

Example: I say we should support affirmative action. White males have run the country for 500 years. They run most of government and industry today. You can't deny that this sort of discrimination is intolerable. (The author has proven that there is discrimination, but not that affirmative action will end that discrimination.)

Fallacies of Presumption

In these the mistaken arguments arise from reliance upon some propositions that are assumed to be true, but are in fact false, or dubious, or without warrant. We have explained the types of reasoning mistakes in five fallacies of presumption:

1. Complex question: When a question is asked in such a way as to presuppose the truth of some assumption buried in that question.

Example: Don't you support home education and the God-given right of parents to raise their children according to their own beliefs?

2. False cause: When one treats as the cause of a thing what is not really the cause of that thing, or more generally, when one mistakes a correlation for a real causal relationship.

Example: Every time I find a penny in the parking lot at the 7/11 I always win some money in the lottery that day. Well, guess what? I found a penny today so therefore, I'm a lotto winner for sure.

3. Begging the question (petitio principii): when one assumes in the premises of an argument the truth of what one seeks to establish in the conclusion of that argument.

Example: The reason I'm so popular is that everybody likes me.

4. Accident: When one applies a generalization in principle or general rule to an individual case that it does not properly govern.

Example: As a general rule, men make more money in the marketplace than women do. Therefore, since I'm a man, I make more money than women.

5. Converse Accident: When one moves carelessly or too quickly from a single case to an indefensibly broad generalization.

Example: Oprah Winfrey is a woman and she is paid more money than any male talk-show host. Therefore, female talk-show hosts, as a rule, are paid more money than male talk-show hosts.


Fallacies of Ambiguity

In these, the mistaken arguments are formulated in such a way as to rely on shifts in the meaning of words or phrases, from their use in the premises to their use in the conclusion. We have explained the types of reasoning mistakes in five fallacies of ambiguity:

1. Equivocation: When the same word or phrase is used with two or more meanings, deliberately or accidentally, the formulation of an argument.

Example: If guns are outlawed, then only outlaws will have guns.

2. Amphiboly: When one of the statements in an argument has more than one plausible meaning, because of the loose or awkward way in which the words in that statement have been combined.


3. Accent: When a shift of meaning arises within an argument as a consequence of changes in the emphasis given to its words or parts.

Example: “My name is Schvink, and whady-a-think, I'll press your pants for nothing.”

4. Composition: This fallacy is committed (a) when one reasons mistakenly from the attributes of a part to the attributes of the whole, and (b) when one reasons mistakenly from the attributes of an individual member of some collection to the attributes of the totality of that collection.

Example: I'm thinking of buying a new Macintosh e-book computer and I found out that the onboard speakers are real cheap. Therefore the laptop itself must be real cheap.

5. Division: This fallacy is committed (a) when one reasons mistakenly from the attributes of a whole to the attributes of one of its parts, and (b) when one reasons mistakenly from the attributes of a totality of some collection of entities to the attributes of the individual entities within that collection.

Example: Smith College is a very wealthy college. I'm dating a girl from Smith, so she must be very wealthy.

Comparison: Accident/converse accident v. composition/division

Your success in Exam #2 this weekend will probably depend on your ability to make these distinctions.

First, note that these two pairs belong to DIFFERENT CATEGORIES i.e they occur for two different fundamental reasons.

ACCIDENT/CONVERSE ACCIDENT happen because an unjustified PRESUMPTION is made that either a general rule or principle applies to all cases even atypical cases where it does not apply.

Accident: Converse Accident

On the other hand....

COMPOSITION/DIVISION happen because of an AMBIGUITY inference is made that the attribute of just few members of a whole group imply that the group itself has those attributes or that the attributes of the group itself can be validly applied to each and every member of that group.

Division: Composition
Falsely argues from attributes of the whole group Falsely argues from the attributes of some members of the group
to apply those attributes to each member of that group to apply those attributes to the group itself

Use these links to sharpen your skills in making these distinctions:

Summary & Examples of Informal Fallacies

As we have seen, a fallacy is a mistaken type of argument that may seem to be correct at first blush, but that proves upon examination not to be correct at all. That's why fallacies are mistakes in reasoning. Types of reasoning mistakes that commonly deceive have been given traditional names; three large groups of informal fallacies have been distinguished: the fallacies of relevance, the fallacies of presumption, and the fallacies of ambiguity.


Click the links below and see how consistently and coherently other philosophers agree on this topic.
Helpful Links on Informal Fallacies:


Animated Videos Help You Learn Informal Fallacies

Fallacies can be fun. In fact successful comedians rely on them to misdirect the mind to a false conclusion from stated premises. Some of these You Tube videos are animated with vaguely creepy characters that talk funny. I kind of like them because, as crude as they are, they also ably express the concepts you are studying to master the informal fallacies of relevance, presumption and ambiguity for Exam #2.


The Fallacy Project: Examples of Informal Logical Fallacies from Advertising, Politics, and Popular Culture:

Logical Fallacies in General Part One:


Logical Fallacies in General Part Two:


Accident/Converse Accident fallacy:


False Authority (ad verecundiam):


Post Hoc Propter Ergo Hoc (false cause) Fallacy: