Common Logical Fallacies

Logical Fallacies

flaws in an argument
often subtle
learning to recognize these will:
- strengthen your own arguments and help you critique other’s arguments

Hasty Generalization

generalization based on insufficient evidence; a conclusion drawn on a sample that is not large or representative enough

Example:

Missing the Point

the premises of an argument do support a particular conclusion, but not the conclusion that the arguer actually draws
“the seriousness of a punishment should match the seriousness of the crime. Right now, the punishment for drunk driving may simply be a fine. But drunk driving is a very serious crime that can kill innocent people. So the death penalty should be the punishment for drunk driving.“

Non Sequitur (Doesn’t follow)

a conclusion that does not follow logically from preceding statements or that is based on irrelevant data

False Analogy

the assumption that because two things are alike in some respects, they are alike in others
“If we put humans on the moon, we should be able to find a cure for the common cold“

“Either or” Fallacy

the suggestion that only two alternatives exist when in fact there are more
“Either learn how to program a computer, or you won’t be able to get a decent job after college“

False Cause (post hoc, coincidence vs causality)

the assumption that because one event follows another, the first is the cause of the second
A occurs before B, therefore A is the cause of B

Circular Reasoning/Begging the Question

an argument in which the writer, instead of applying evidence simply restates the point in other language
premises in which the truth of the conclusion is claimed or the truth of the conclusion is assumed
“Students should not be allowed to park in lots now reserved for faculty because those lots should be for faculty only“

Begging the Question

“Active euthanasia is morally acceptable. It is decent, ethical thing to help another human being escape suffering through death"

Bandwagon Appeal

ad populum
a claim that an idea should be accepted because a large number of people favor it or believe it to be true
Peron P is pressured by his/her peers or threatened with rejection, therefore person P’s claim is false

Argument to the person “Against the MAN”

an attack on the person proposing an argument rather than on the argument itself
Person A makes claim X, person B makes an attack on person A, therefore A’s claim is false

Red Herring

an argument that focuses on an irrelevant issue to detract attention from the real issue
Top A is under discussion, Topic B is introduced under the guise of being relevant to topic A (when topic B is actually not relevant to topic A), topic A is abandoned
“I think there is great merit in making the requirements stricter for the graduate students“ topic A
“I recommend that you support it, too“ claim
“After all, we are in a budget crisis and we do not want our salaries affected“ topic B

Force and Fear (Ad Baculum)

used whenever the proponent of an argument attempts to persuade the audience to accept the conclusion…by predicting (or causing) unpleasant consequences if it is not accepted
“You will do this or else“

Appeal to Celebrity/Authority

consists of an appeal to irrelevant authority
- an authority who is not an authority in the field of question
“Oprah says that she won’t eat beef, therefore you shouldn’t eat beef“

Pity (Ad Misericordiam)

appeal to accept the truth of a conclusion out of pity for the arguer or some third party
either the arguer is already an object of pity, or they will become one if the conclusion is not accepted

Non Disproof

one sometimes encounters arguments that some claim should be accepted because they have never been disproved, the move from “not disproved“ to “proved“ is invalid
no one has ever shown that it is impossible that the stars rule our lives; therefore, astrology is true

Undistributed Middle

an error in deductive reasoning in which the parts of a premise may, or may not, overlap
the middle term is undisturbed in that all instances of a conclusion are also instances of the premise
valid argument: all mammals have hair, all whales are mammals. all whales have hair
invalid argument: all whales have hair, all humans have hair, all whales are human

Weak Analogy (Straw Man)

analogy: comparison
weak comparison
we assume that just because something is alike in some regards that it’s alike in all regards
“Guns are like hammers- they’re both tools with metal parts that could be used to kill someone. And yet it would be ridiculous to restrict the purchase of hammers, so restrictions on purchasing guns are equally ridiculous“

Slippery Slope

leading one negative thing to another (chain of events)
“If I don’t pass this class, I won’t get into college, if I don’t get into college, I can’t get a job, if I don’t get a job, then I’ll live in my car“

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