Arguments
When logicians talk about arguments, they don't mean what happens on the Jerry Springer show. Instead they mean a logical argument, consisting of one or more premises (pieces of evidence or reason) and a conclusion. For example:
(P) All birds have feathers
(P) Ostriches are birds
(C) Ostriches have feathers.
Sometimes one or more of the premises, or the conclusion, is not stated but are unexpressed or implied:
(P) Ostriches are birds
(P) (Not stated, but expected to be known: All birds have feathers.)
(C) Ostriches have feathers.
In complex arguments the conclusion of one argument is used as a premise in another argument:
(C2) [You should] Vote for Smith. (Note that here the conclusion comes before the premises.)
(Conclusion of the following argument, and the premise for C2, and often implied rather than stated): She is the best candidate for the job.
(P) She has years of experience.
(P) She was endorsed by all the local papers.
(P) Etc.
Arguments can often be identified by argument indicators. Here are some of the more common argument indicators (from Perkins, page 6):
because
since
for
inasmuch as
for the reason that
due to the fact that
as
after all
Conclusions can also frequently be identified by conclusion indicators. Here are some common conclusion indicators (from Perkins, page 6);
so
therefore
thus
hence
it follows that
Arguments can be classified as deductive and inductive. In a deductive argument, if the premises are true and the argument is valid, the the conclusion must be true. The first example on this page is a valid deductive argument. In an invalid argument, the conclusion is not necessarily true, even when the premises are true. In this case a formal fallacy has been committed. For example:
(P) All men are mortal.
(P) Elizabeth Taylor is mortal.
(C) Elizabeth Taylor is a man.
Here the conclusion is false, Elizabeth Taylor is not a man (This is an example of the fallacy of affirmation of the consequent.)
In an inductive argument, if the premises are true then the conclusion may be true. Inductive arguments can be divided into weak arguments (with a low probability that the conclusion is true) and strong arguments (with a high probability that the conclusion is true). Errors of logic in inductive arguments are called informal fallacies. Some examples:
(P) I heard John arguing with Steve an hour before Steve was murdered.
(C) John must be the murderer.
This would be a weak argument. While an argument may be a motive for murder, it is not very strong evidence. This is a much stronger argument:
(P) I heard John arguing with Steve an hour before Steve was murdered.
(P) John's fingerprints were all over the murder weapon.
(P) John confessed to the police that he did it.
(C) John must be the murderer.
Finally, even if the premises are wrong or there is a fallacy does not mena that he conclusion is wrong ((Concluding that the conclusion is wrong because there has been a fallacy is known as the logical fallacy or fallacy fallacy.) Example:
(P) All birds can fly.
(P) Bats are birds.
(C) Bats can fly
Neither of the premises is true. Some species of birds cannot fly, and bats are mammals. But the conclusion is still true.
Reference
Ray Perkins, Jr., Logic and Mr. Limbaugh: A Dittohead's Guide to Fallacious Reasoning, Open Court, 1995
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Written by Jim Norton
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