A fallacy is a defect in an argument. A formal fallacy is a defect in the form or structure of an argument. Since deductive arguments depend on formal properties and inductive arguments don't, formal fallacies apply only to deductive arguments. Informal fallacies are defects found in the content of the argument, which could be inductive or deductive.
There are many ways arguments can be defective.
Some defects are common enough to warrant a name. And many common defects
are similar enough to warrant classification.
The premises may be psychologically but not
logically relevant to the conclusion. Logically relevant premises contribute
to our ability to see that the conclusion is true. In this sense we have
reason to believe that the conclusion is true. Psychologically relevant
premises may give us some reason to believe the conclusion is true but
not because they help us see that the conclusion is true.
The fallacy occurs whenever the arguer presents a threat under the pretense of defending a conclusion. Premises that threaten are not relevant to the truth of the conclusion.
Threat must occur in the context of an argument.
Threats may involve physical or psychological harm.
Threats may be direct or veiled.
Arguer attempts to get an audience to accept a conclusion by evoking pity or sympathy.
Pity could be directed at the arguer or some third party.
Some arguments from compassion are not fallacious;
but they must supply some evidence that the pity or compassion is justified
and that the recommended response is reasonable.
The arguer exploits common desires to be loved, accepted, admired, etc. to get the audience to accept the conclusion.
The direct approach is used when arguer excites the emotions of a crowd to win acceptance for a conclusion; mob mentality
The indirect approach is used when the arguer
targets an individual and exploits the individual's desire to be accepted
or respected. The bandwagon argument; appeal to snobbery; appeal to vanity.
Two arguers: One presents an argument and the other responds by redirecting attention away from the argument and towards the arguer. The question of whether the premises support the conclusion are ignored. But the merits of an argument are independent of the character of the arguer.
Abusive version: respondent verbally abuses the arguer and ignores the argument.
Circumstantial version: respondent calls attention to special circumstances of the arguer and ignores the argument.
Tu quoque: respondent attempts to make the arguer look hypocritical.
Sometimes the character of a witness or informant are relevant to the credibility of testimony.
Sometimes it is fair to consider the character of the arguer before we accept the premises of an argument.
The fallacy (against the person) occurs only
when the person attacked is an arguer and when our attention is drawn from
the character of the argument and to the character of the arguer.
Accident occurs when a general rule is applied to a case it was not meant to cover.
You should be able to see what the general
rule is and why the specific case mentioned does not apply.
This fallacy is committed when the respondent distorts an argument, demolished the distortion, and then concludes that the original argument was demolished.
Involves two arguers.
The distortion (the "straw man") is usually easier to attack.
The respondent pretends to have attacked
to original argument, so the distortion is in some related to or similar
to the original argument. Sometimes the distortion is an exaggeration of
the original argument.
The premises of one argument support a particular conclusion but another vaguely related conclusion is drawn instead.
The missing the point fallacy is a specific kind of fallacy of relevance.
Typically the arguer misunderstands the logical implications of the premises.
You should be able to identify the correct
conclusion.
The arguer shifts attention from the original subject to a related subject.
Typically the arguer never returns to the original subject.
The red herring differs from the straw man in that the latter involves a distorted argument and the former involves a change of subject; the latter also requires two arguers, the former doesn't.
The red herring and straw man differ from missing the point in that the former involve generating new sets of premises; for the latter the conclusion is irrelevant to the premises but not so for the former.