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The following is a philosophy article by Scott Hughes. Posted March 7th, 2010.
On the Philosophy Forums, people post arguments for others to review and critique. In everyday life, even an illogical argument can persuade people. Such arguments can be called irrationally convincing. In contrast, a truly good, logical argument is rational and persuasive not because it appeals to irrational people or tricks generally rational people into thinking it is rational when it is not, but rather it is convincing because it communicates its logic and evidence well. People post their arguments on the Philosophy Forums so that the other members' critiques can help determine whether the argument is sound or whether it is fallacious or otherwise unsound or not rationally convincing. While an irrationally convincing argument may persuade people and have practical uses in general life despite being illogical or otherwise unsound, the members on the Philosophy Forums are better at spotting fallacies or other problems with an argument from a rational point of view.
I think a good, complete, logical argument that is to be rationally convincing generally has 4 elements. When I say 'good argument' in the rest of this article, I am referring to the type of argument that is made in a genuine attempt to be logical and rationally convincing NOT the irrationally convincing kind of so-called argument.
Premises - A logical argument must have premises. A good, complete argument clearly states those premises and identifies them as premises. Premises are declarative statements known as propositions from which the conclusion is concluded. They are the assumptions.
Sources - A good, convincing argument will have sources for the premises. The argument is not sound if any of the premises are false. So the argument won't be convincing to a reader if the reader doubts any of the premises. Even if you think something is common knowledge or obviously true, another person may not be completely sure it is true. Besides, many things that are commonly believed to be true are not. Sources may be exempted from premises that are self-evident and if a good source cannot be provided for that reason. But if a source can be found even for something well-known, self-evident or true by definition, then use it. For instance, even something as blatantly true by definition as the proposition, "Dogs are mammals," or "If you are overweight, than you weigh more than is considered healthy," can be easily be sourced by checking an encyclopedia or dictionary. By using sources when possible even for a proposition that you think is self-evident or obvious, you avoid the risk of failing to use a source when needed because you falsely considered something self-evident that is not.
Logic/Inferences - The inferences are the logic or fallacy that is used to conclude the conclusion. The inference is either logically valid or fallacious. It is important to note that the argument can still be logical even if the premises are false.
Conclusions - The conclusion is what is concluded from the premises through supposedly logical inference. Logically, the conclusion cannot be false if all the premises are true and the argument is logically valid. However, the conclusion may be false if any of the premises are false and/or if the argument is illogical. Of course, the conclusion could still happen to be true by coincidence even if one or more of the premises are false and/or the argument is illogical. Indeed, it would be a fallacy itself to conclude a proposition is false merely because it happened to be the conclusion in an unsound argument.
If readers of the argument want to attempt to rebut the argument, they must attack the truth of the premises or the validity of the logic. One can attack the truth of any or all of the premises by attacking the credibility of the source(s) of the premise(s) or by providing more credible sources saying the premise is false. One can attack the validity of the logic by pointing out a logical fallacy.
Premise 1: A pointblank gun shot to the approximate center of one's forehead head will almost certainly kill a person. (Source: Dr. Joe Shmoe, MD)
Premise 2: John Pretendstein was shot pointblank in the center of his forehead. (Source: Officer Ted Fakeperson, lead officer on case)
Conclusion: Therefore, John is almost certainly dead.
As you can see, though pretend, the above argument has all four elements described.
The post by Alun entitled "Reasons Behind the Theory of Evolution by Natural Selection" is a great example of a good, complete logical argument. In it, he uses color-coding to disguinish premises from conclusions, he provides many sources with links, and he provides numbers for each premise, source and conclusion to make it easy for responders to specify which premise, source, inference or conclusion they wish to address or refer at any given time while responding.