The errors can be categorized into four groups of four. There are Errors of Identity, Errors of Causality, Errors of Logic, and Errors of Reason.
Errors of Identity occur when the identity of the speaker makes a difference on the evaluation of an argument. But an argument is true and valid on its own, irrespective of who poses the argument.
Errors of Causality occur when cause and effect are muddled, such that some other relationship is accepted in place of true cause and effect.
Errors of Logic occur when fundamental semantic rules of order are broken.
Errors of Reason occur when a communication other than sound information is utilized in the evaluation of an argument. An argument is true and valid irrespective of, for example, the volume at which the argument is posed.
Errors of Identity
Ad Hominem
“Of the man.” Literally, you should believe or not believe an argument because of the identity of the speaker. When in fact, the truth or validity of an argument exists irrespective of who spoke or originated the idea.
Example: “Project X is a waste of time. Joe says so.”
(Project X being a waste of time should be evaluated on its own merits, not because the idea originated with Joe. Joe may be wrong.)
Hypocrisy
To turn an argument from a discussion of the argument to a discussion of the character of the speaker. So literally, evaluation of the argument stops in favor of evaluation of the character of a person.
Example: “Bill thinks Project X is too expensive. Of course Bill thinks a lot of things are too expensive.”
(Now we are talking about Bill instead of about Project X. The subject changed.)
Prejudice and Stereotype
Prejudice is literally pre-judging arguments because of beliefs about the nature of the speaker, such as their intention, capabilities, or believability. Stereotype is when a pre-judging is applied to a group, and then the speaker is ascribed membership in the group, and therefore their argument is pre-judged. In prejudice and stereotype the argument is never evaluated because evaluation stops in favor of a foregone conclusion. The listener literally stops thinking.
Example: “Joe says we should do Project X. But Joe is in QQBU. And you know you can't trust anything they say.”
(Really? Everything that people in QQBU say? All the members? All the time?)
Anthropomorphizing
Ascribing human characteristics to objects or concepts. The human character is then used as an assertion for believing or disbelieving an argument.
Example: “We can't do Project X. We don't want to make QQBU mad.”
(QQBU cannot become made, it is an organization, not person.)
Errors of Causality
Post Hoc Ergo Propter Hoc
Before, therefore because.
Example: “Joe said we were going to reach our goal, and then we did.”
(That doesn't mean Joe's speech had any effect on us reaching our goal. It just occurred earlier in time. Perhaps it was a coincidence.)
Subtype: Cum Hoc Ergo Propter Hoc
Cause and effect assumed when things occur at the same time.
Subtype: Ad Hoc
Information is added to try to make the argument seem true.
Oversimplification
A series of premises in combination are the cause of something, and one premises is raised in importance above all others as if it were the sole cause.
Example: “We could not have accomplished Project X without good planning. That's what made Project X a success.”
(Project X is planned, resourced, and executed. The other critical elements have been diminished in importance. Planning was only one cause.)
Anecdotal Evidence
A story or anecdote is used as a premise rather than facts, implying that the circumstance in the story is true in all cases, when in fact the story may not convey a general truth or may not be true at all.
Example: “Joe worked on something like Project X, and it didn't pan out. So we shouldn't go down that path again.”
(Why didn't Project X pan out? Joe's experience is one data point. It may not apply to all circumstances, to the current circumstance, and it might not even be true. Where's Joe?)
Invalid Assumption
A premise of an argument is unverified, and perhaps not even true. The assertion may be unsupported, meaning presented without any evidence whatsoever that it is actually the case. It may be based on partial or incomplete evidence. Or the assertion may be based on suppressed evidence, meaning that the speaker refuses to provide examples demonstrating that the assertion is true.
Example: “These things never work out. So let's not even go there.”
(Never? What evidence do you have to support that?)
Errors of Logic
Non Sequitur
Reversing premises as if the relationship is symmetric, when in fact it is not, leading to an invalid conclusion.
Subtype: Affirming the Consequent
1) If A, then B.
2) B.
3) Therefore A.
Example:
If I am in San Jose , then I am in California . I am in California . Therefore I must be in San Jose .
(Couldn't I be in Los Gatos ?)
--or—
Subtype: Denying the Antecedent
1) If A, then B.
2) NOT B.
3) Therefore, NOT A.
Example:
If I am in San Jose , then I am in California .
I am NOT in California .
Therefore I am not in San Jose .
(Couldn't I be in San Jose , Costa Rica ?)
Circular Reasoning
One of the premises of the argument contains or implies the conclusion.
Example: “The programming class is necessary because everyone needs it.”
Begging the Question (Petitio Principii)
The argument rests on a premise which is to be evaluated, but the truth of the premise is implied or assumed in the argument.
Example: “All engineers need this class. The fact that engineers attend the class is proof of this.”
(It relies upon its own proposition to support its central premise. In this case the idea that “attendance of the class implies general need” is an unproven assumption).
Hasty Generalization
Inductive generalization is reached based on too few instances of data or experiences. Often involves a broad conclusion based on a small statistical sample.
Errors of Reason
False Dilemma (Either/Or Dilemma, Black and white thinking)
A dichotomy (either one way OR the other) is believed to exist, even though there may be more than two alternative states of existence.
Subtype: Contradiction
An assertion is made that a thing must be BOTH one way AND another way, when the two states are opposite or incompatible.
Irrelevance
Information which is irrelevant to the evaluation of an argument is tossed in to confound evaluation and assessment of truth.
Subtype: Irrelevant Conclusion (Red Herring)
Premises which are true are paired with a conclusion that has nothing to do with them, in an effort to confuse or distract the listener from evaluation of the argument.
Subtype: Faulty Analogy
An analogy is taken too far, or is inappropriate for the circumstance and therefore leads to an incorrect conclusion.
Subtype: Genetic Fallacy
The significance of an idea or thing is reduced to its origins or an earlier form in its development. Example: “Einstein flunked math when he was a child. So you can't put much faith in his theories.”
Bias (Appeals)
An argument to emotion rather than reason.
Subtype: Argumentum ad Baculum (Appeal to consequences)
If you don't believe this you'll be beaten up.
Subtype: Appeal to Authority
Believe this because the President said so.
Subtype: Appeal to Pity
Believe this and all the little animals will be saved.
Subtype: Appeal to the Majority (Bandwagon, Appeal to Numbers)
Are you kidding? Everyone believes this.
Surveys say that 5 out of 4 people agree.
Subtype: Appeal to Probability
Chances are – I'm right.
Subtype: Appeal to Tradition
We've always done it this way.
The reasons are buried in antiquity.
Equivocation (Ambiguity)
Two items are taken to be equivalent when they are not. Or two items which are part of the same thing cannot be separated, isolated, or clearly defined. (The opposite of equivocation is disambiguation). By including an equivocation, the discussion may move to attempting to disambiguate the definition of the premise rather than focusing on the validity of the original argument. If the people are unsuccessful in reaching an agreed definition to disambiguate the items, then the discussion may never return to the original argument.