Logical Arguments and FallaciesThe formulation of valid logical arguments is one of the pillars of the Scientific Method. An argument consists of one or more premises and one conclusion. A premise is a statement that is offered in support of the conclusion. Premises and conclusions are statements that may be true or false. A valid logical argument presents true premises that logically lead to a true conclusion. Arguments may be either deductive or inductive. The premises in deductive arguments provide complete support for the conclusion, whereas for inductive arguments they provide some degree of support, but not complete support. Fallacies are arguments that are defective because the premises do not provide the proper support for the conclusion. These are the most common fallacies:
An Ad Hominem fallacy is an argument which is used to discredit what a person said by attacking the person rather than by disproving the statement. An Ad Hominem fallacy is invalid logic because the character, circumstances, or actions of a person are not relevant to the truth or falsity of the claim being made. For example, in the argument "President Bush is a bad president because he goofed off in college", the conclusion that President Bush is a bad president may be true, but the statement that he goofed off in college which may also be true does not provide enough support for the conclusion.
An Appeal to Authority is an argument where the premise references an authority to support the argument. Appeals to authority may be wrong when the authority is not a reliable reference for a particular subject, for example: "President Bush said that our mission in Iraq was accomplished therefore it must be true".
Appeal to Ridicule is a fallacy in which ridicule or mockery is used in the premise as a justification for the conclusion. For example, "Copernicus said that the Earth goes around the sun. He is crazy!" Ridiculing Copernicus does not disprove that the Earth goes around the sun.
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