Logical Fallacies in Writing
This page offers a list of common logical fallacies. But first, what is a logical fallacy? A logical fallacy is an inaccurate or intentionally misleading misapplication of logic. The words "therefore" and "thus" are frequently misused connection words, meaning "consequently" or "it follows that...". They signal a conclusion to the reader. The words are essentially interchangeable; however, "therefore" seems to emphasize a logical connection, while "thus" seems to imply a causal, chronological sequence.
Proper Use of Logic Words
1) Socrates is a man. All men are mortal. Therefore, Socrates is mortal. Simple transference. The definition of "man" includes the concept "mortal being". If you know Socrates fits all the criteria for being a man, then he fits all the criteria for being mortal. But "Socratese is mortal, all men are mortals, therefore Socrates is a man" is false. (Socrates may be a pet guppy -- mortal, but not a man.)
2) The water droplets are too heavy for the atmosphere to support. Thus, they fall to the ground as rain. Cause-and-effect. Heavy things push light things out of the way and sink. (But did the droplets become heavier, or did the atmosphere change so that it is capable of supporting less weight? This sentence doesn't answer that question.)
3) Plants and animals must coexist on earth in order for life to continue. Therefore, plants provide animals with oxygen, and animals provide plants with carbon dioxide. Yes, plants and animals coexist, yes, life on earth continues. But this example contains an unexamined premise ("life on earth must continue") that turns out to be a red herring; it works its way into the equation, distracting the reader from the real issue. Life continues because of the arrangement between plants and animals; the plants and animals did not adopt their behavior because they were motivated by the imperative to continue life on earth.
4) There must be a constant flow of water; thus, nature provides a way for water to get from the end of a stream back to the beginning. The premise "water must return to the beginning of a stream" is weak, because it begs the question. By definition a stream is a constant flow of water. Once the flow stops, you no longer have a stream. Therefore, if you've got a stream, it's because you've got a constant (presumably replenishable) source of water.
We can salvage the two faulty examples, but doing so affects the outcome of the statements:
3A) Plants and animals are symbiotic: therefore, life on earth continues. Nature brings water from the end of a river back to the beginning; thus, a stream can flow constantly.
List of Common Logical Fallacies
| False Dichotomy Ad Hominem Non Sequitur Hasty Generalization Circular Reasoning |
Red Herring
Loading the Question Slippery Slope Post Hoc (Ergo Proper Hoc) More (links) |
Take
it or leave it. (Why not change
it?)- If
you aren't part of the solution, you're part of the problem.
Ad Hominem ("to the person": an attack directed on the character of an opponent, rather than the issue at hand)- You would
say that; you're a crazy liberal tree-hugger.
- Applying labels shuts down your thought process too quickly.
Bill
Clinton is a bad president because he is an unfaithful
husband.- If the topic of your discussion is Clinton's personal character, this statement might be acceptable -- but you would have to construct an argument tying both performance as president and behavior as a husband back to the same character traits.
- Fred
attacks Clinton's character simply because Fred hates
liberals.
- If the point of the argument is Clinton's character, then Fred's critiques of Clinton are valid (or invalid) regardless of Fred's character. Someone who attacks Fred is doing so becasue he or she cannot defend Clinton's character against Fred's attacks. Resorting to an ad hominem attack is a sign of weakness.
- This car has
a noisy engine; therefore, it must be fast.
- Because I drink
a six-pack a day, sexy young chicks will come flocking
to me.
- Beer companies get rich because lots of college men behave as if this were true!
- If you build
it, they will come; you did not build it, therefore, they
will not come.
- To make this work, you would have to prove that "to build it" is the only way to make "them come".
- Most of the
people in the room opposed the project, so most people
in the town probably oppose it, too.
- Unless you can prove the sample in the room were statistically representative of the town as a whole, you cannot make this claim.
- Nobody at the
rally in favor of X said anything about the terrible evil
of Y. I guess everyone who supports X must also
be in favor of Y.
- You can't use the absence of evidence to prove anything!
- The
standard written English you will learn in this course
is defined as the writing style most often employed by
college-educated people.
- A
good person is someone who does good things. If
I do good things, then I am a good person.
- If I hadn't
done it, somebody else would have, so it's not really
my fault.
- I work 60 hours
a week to support my family, and I pay my taxes; you shouldn't
arrest me just because I punched him in the face.
- When did you
stop beating your spouse?
- Assumptions = 1) you have a spouse 2) you have beaten your spouse
- Increased police
presence on the highways is the best way to stop motorists
from abusing toll-booth attendants.
- Assumption = The motorists' behavior towards toll-booth attendants is abusive.
- First, medicinal
wine from a teaspoon... and then, beer from a bottle!
Soon, you'll be an alcoholic.
- If we let them
ban machine guns and assault weapons, next they'll try
to take away our hunting rifles, BB guns and water pistols!
Are we going to stand for that?
- A flood happened
after the comet appeared; therefore, the comet caused
the flood.
- Specific Logical Fallacies (Lee Ann Mortensen, Utah Valley State College)
- The Logical
Fallacies: Index (Stephen Downes, Assiboine Community College)
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