(The following is a handout from my days of teaching first year composition at university. It is meant to be a very basic introduction to the complicated study of logical fallacies. Anyone who finds it useful can reproduce it, so long as they give me credit for it)
For thousands of years, people have been cataloging invalid arguments. These are arguments are invalid largely because they are illogical. That does not mean that they cannot be extremely effective; the associational fallacy, for example, is the basis of a good deal of advertising. But the illogic does mean that they should not be accepted in an essay, which is meant to be the construction of a logical structure of ideas.
Too large a conclusion is drawn from too specific evidence.
Example: Three regional airlines have just gone bankrupt, and many of the larger lines have discontinued flights on certain routes. The North American commercial transportation system is in chaos.
Airlines are not the only form of commercial transportation, and bankruptcies and discontinued routes might not be enough to justify calling the result “chaos.”
Too many considerations are left out for the conclusion to be valid.
Example: Getting a good grade in English is easy. All you have to do is write essays of the required length and repeat the teacher’s opinion.
Grammar and punctuation, structure, and even original thought are also factors in getting a good grade.
Only two extreme positions are acknowledged, and no alternatives or mixed positions. Sometimes called “the excluded middle.”
a.) America: love it or leave it (a statement made by political conservatives in the 1960s)
b.)What do you want: good grammar or good taste? (a slogan once used by Winston cigarettes)
You can criticize your country and still want to live there, and good grammar has no relation to good taste, so it can hardly be its opposite.
Post hoc ergo procter hoc (Latin, “after this, therefore that”)
Because one event occurs after another, it must be caused by the second event.
Example: I carry a gun so I won’t be robbed. It must work. After I was robbed a year ago, I started carrying a gun, and I haven’t been robbed since.
From this statement alone, you can’t be sure of any cause or effect. The speaker may not be going to the same parts of town as before, or maybe they have just been lucky.
Non sequitur (Latin, “it does not follow”)
No logic exists between two parts of an argument
a.) “I made the decision myself, because if we listened to experts, we’d have a tyranny of expertise, and then where would we be?” (John Fraser, former Minister of Fisheries)
b.) “I couldn’t have kicked that girl to death. I wear soft shoes” (a murder’s explanation of why he was innocent)
Why should Fraser insist on making the decision when the whole point of experts is to have someone with advice worth listening to? Similarly, you can still kick with soft shoes – or even when you’re barefoot.
A poor choice of metaphors or of similar situations.
a.) Some people cannot be educated. You can’t make a silk purse out of a sow’s ear.
b.) A well-run office is like a machine. You should be able to replace people without disturbing the office’s efficiency, just as you can replace a bolt or a gear in a machine.
You can’t make a silk purse out of a sow’s ear, because silk isn’t made of pigskin, but it’s not clear that people are that inflexible.
As for an office being like a machine, every organization has an informal organization that compensates for problems with the official organization. For instance, a receptionist may compensate for a company officer’s inability to keep to deadlines. Replace that receptionist, and the office may become disorganized.
Ad Hominem (Latin, “to the person”)
Attacking the person who holds the argument, not the argument itself.
a.) People who complain about the conduct of Cabinet Ministers have a vested interest in attacking the government.
b.) Ignore what teachers tell you about writing. They’re all frustrated journalists and novelists who aren’t good enough to compete in the commercial market.
Both these statements may be true or false. But, either way, they do no mean that the attack isn’t valid or that their advice isn’t worth following.
Ad Populum (Latin, “to the population”)
An argument that appeals to popular prejudice or belief.
a.) Canadians have worked too hard to see their jobs stolen by recent immigrants, or, even worse, to support them when they go on welfare or unemployment.
b.) Everyone is entitled to an opinion.
The first example tries to appeal to anti-immigration prejudice, the second to the popular wisdom of a cliché. Neither replaces a reasoned argument.
A position is made attractive by who holds it – either a famous person, or people with desirable qualities.
Example: I have no crystal ball. But based on our previous mailings, I’m willing to go out on a limb and make a prediction –
Of all the people who receive this invitation, only a very special group will select accept.
You can easily spot them in any crowd. The young in mind, no matter what their age. Eternally curious. Open to new ideas. Alert to future possibilities. Those fortunate few who didn’t stop growing – intellectually – the day they left school. (a magazine subscription offer in the mail)
The implication is that, if you subscribe, you will prove yourself open-minded and curious, too.
Appeal to Authority
A position must be correct because of who holds it. Alternatively, some greater force such as God or a natural order may be mentioned. Note that this has nothing to do with citing who you got an idea from.
a.) Biology is destiny. Women must be dependent on men.
b.) It is historically inevitable that capitalism give way to socialism.
Here, “biology” and “historical inevitability” are represented as greater than human forces with which no one can argue.
An argument in which the first statement depends on the second, and the second on the first.
Example: There are no drafts of the last half of the poem because Shelley never finished it. If he had finished it, we would have had the drafts.
Besides being faulty reasoning in other ways (the drafts could have been lost), this argument simply goes round and round.
Similar to a circular argument, the second statement simply repeats the first one – bu tthe repetition is disguised because of a change in wording.
a.) Opium puts people to sleep because it contains a dormitive principle.
b.) Ted Bundy killed young girls without remorse because he was a sociopath with a disturbed libido.
“Dormitive” is an adjective that refers to sleep, and a sociopath does things without remorse.
A position is attacked or defended because of its moral or ethical qualities.
a.) That is an evil position to hold.
b.) My plan is simply common sense.
Arguments are supposed to be about logic. The morality or ethics of them are irrelevant.
A word or phrase is repeated, but with a different meaning each time.
a.) The law is clear on this point. You can’t argue against it any more than you can argue against the law of gravity.
b.) Since evolution is just a theory, my theory about the origins of life are just as good as any biologist’s.
You can’t argue against gravity because it is a description of how the universe works, but the laws of a country are made by humans and regularly argued. Similarly, a theory is just below a law in science – a position that best explains the evidence – while a “theory” in ordinary conversation is just an opinion.
Confusion of Logical Types
A logical type is a level of organization. For example, a body is of a higher logical type than an organ like the liver, and an organ is of a higher logical type than a cell. You cannot compare or contrast different logical types because they create the absurdity of the parts of something being discussed as equal to the thing itself.
a.) The needs of the individual are more important than the needs of society.
b.) Ignore the details and concentrate on the larger picture.
Give too much priority to either the individual’s or society’s needs, and you are likely to have trouble. In much the same way, the larger picture is composed of details, so you cannot ignore them.