In short: an argument tries to persuade someone of something. An argument may appeal to logic, ethics, or emotions (among other things). As a strategy, an argument may invoke facts, statistics, anecdotes, authorities, humor, analogy, etc.. Some strategies are more effective than others. Arguments that are (or should be!) generally ineffective are called fallacies. (Sadly, some fallacies occur so often because they are psychologically appealing, even though they are examples of poor reasoning, and thus likely to lead you to error. If that weren't true, there would be no need for this course.)
A general review: an argument is a connected set of statements (premises) intended to establish a particular conclusion. (A conclusion is also a statement.) There are good and bad arguments. Traditionally, we say that good arguments are sound. This is a very strong requirement. Not only must all the premises be true, but the reasoning must be valid.
A valid argument is such that if you accept the premises, then you must accept the conclusion. In philosophy, we say that the premises entail the conclusion. If the premises do not entail the conclusion, the argument is relatively weak.
In this course we have not looked at all of the ways a set of premises may entail a conclusion. That study is better pursued in formal logic. We have borrowed a little. Here is a sample. Given the premise, "If you are human, you are mortal", and the premise "You are human," then you must conclude that you are mortal. If you would like to know why, or indeed, what happens if you deny that conclusion, you should study formal logic and alternative logics. But be advised that using alternative logics in normal reasoning will probably make you seem daft.
Formally, a reductio is a proof that the premise under question leads to a contradiction with other known premises, thus proving the negation of the questioned premise. (Well, technically, it could be any of the assumed premises that are in error, but usually most are very firmly established and one is being questioned.)
A fallacy is an error of reasoning. Another way to say this is to say that a fallacy is an argument that is perceived to be weak or flawed for various reasons and thus is ineffective.
A fallacy is not a factual error.
An invalid argument is always a
fallacy. (Example: denying the consequent) However, a
fallacy is not always a formally invalid
argument. (Example: begging the question).
It is useful to learn twenty or so of the
common fallacies to sharpen your ability to spot weak
argumentation in discussions, in the media, in your reading, and
in your own writing. Logicians have named around 300 fallacies
although lists in texts seldom exceed
30. Links to more comprehensive lists with
more complete explanations are given at the end. This list is
taken in part from Sylan Barnet’s and Hugo Bedau’s
Current Issues & Enduring
Questions(1999): AD HOMINEM—(from Latin for "against the person")
attempts to discredit an argument by attacking the person making
it. (Arthur has been arguing against capital punishment. But
Arthur is a jerk, so you shouldn't believe him.) AFFIRMING THE CONSEQUENT— This fallacy is an argument of
the form "A implies B, B is true, therefore A is true". The
fallacy is to invalidly conclude that the antecedent (A)
must be true because the consequent (B) is true. (All men
are mortal. Fido is mortal. Therefore Fido is a man.) Converse of
Denying the Antecedent.
AMBIGUITY—using terms or phrases that have too many
meanings, that can be interpreted different ways: (People have
equal rights so everyone has a right to property.) See also
Equivocation APPEAL TO AUTHORITY—the authority of a person in itself is
not evidence for the truth of his or her views. We see this all
the time on television commercials. APPEAL TO IGNORANCE—invites the audience to draw an
inference from a premise that is unquestionably true—but what
is that premise? It asserts that there is something we don’t
know, but what we don’t know cannot be evidence for or
against anything: (Since we don’t know how many people the
death penalty has deterred from committing murder, we
shouldn’t abolish it.) BEGGING THE QUESTION—the conclusion of the argument is
actually one of its assumptions and so it’s not surprising
that the conclusion follows (is validly deduced from)
from the premises: (Thank the death penalty that you were not
murdered yesterday.) (Both a premise and the conclusion of this is
that the death penalty is an effective deterrent.) COMPOSITION—arguing from the true premise that each member
of a group has a certain quality to the false conclusion that the
group itself has the quality: (A team of five NBA all-stars is the
best team in basketball if each of the five players is the best at
this position.) This is also called the "part-to-whole"
fallacy. DENYING THE ANTECEDENT— This fallacy is an argument of the
form "A implies B, A is false, therefore B is false". The fallacy
is to invalidly conclude the opposite of the consequent (B)
because you have denied (or negated the
antecedent (A). (All men are mortal. Fido is not a
man. Therefore Fido is immortal.)
DIVISION—To argue from a quality of a group to a quality
of a member of that group. (The average American family has 1.8
children, so it is likely that you will came from a family of 1.8
children.) EQUIVOCATION— changing the meaning of a word between steps
of the argument. (Nothing is better than a thick, juicy steak. A
crust of bread is better than nothing. So a crust of bread is
better than a thick juicy steak.) See also Ambiguity FALSE ANALOGY—this occurs when a questionable comparison
is made between different things. GENETIC FALLACY—arguing against some claim by pointing out
that its origin (genesis) is tainted or that it was invented by
someone deserving our contempt: attacking the ideas of the
Declaration of Independence by pointing out that its principal
author, Thomas Jefferson, was a slaveholder. HEAP—Concluding that there is no real difference
merely because there is no clear difference. (A grain of
sand is not a heap. No matter how much sand you have, if it is not
already a heap, adding one grain won't make it a heap. Therefore
there are no heaps of sand.) In class, I lumped this in with
slippery slope.
MANY QUESTIONS—The proposition is stated as a question
that itself contains too many implicit questions. (Are you going to
fail this test now or next week? When did you stop beating your wife?) POISONING THE WELL—the attempt to shift the merits of an
argument to the source or origin of the argument. (The ERA
Amendment is a communist plot because Marx and Engels advocated
it.) SLIPPERY SLOPE—If we do this, it will be the first step
down the path that leads to ruin. Heard as a frequent argument against any
type of government regulation. Remember the "Brave New World" and
"Totalitarian" arguments in the Clone debate. In class I grouped this with
the Heap fallacy. Here I have distinguished them.
Some common
fallacies (although they are all used as argument strategies
too) with quick definitions and very simple examples
which should make it clear why these reasoning forms are
fallacies. The problem with simple examples is that
they make you think the fallacy is always easy to spot. Please
see the lecture notes and homework for more subtle
examples.
More comprehensive fallacy lists
The following links appear to be the most comprehensive and most
referred-to fallacies lists on the web.
Charles Twardy
Last modified: Fri May 11 11:53:57 EST 2001