Logical Fallacies I've been noticing many people using logical fallacies in their arguments here and felt this needed to be covered. Using a logical fallacy renders your argument invalid, so they should be avoided. I'm going to cover some of the more common logical fallacies so you can learn to recognize them and not use them anymore. Ad Hominem (to the man) - This logical fallacy occurs when the person is attacked rather than addressing the issues they raise. It's a fallacy because even if the characteristics mentioned in the attack are true it has no bearing on the truth value of the person's argument. Ad Populum (to the people) - This logical fallacy takes the form of "most people believe X is true, therefore X must be true". It is a fallacy because reality does not conform itself to public opinion. the number of people that believe something have no bearing on its truth value. Bandwagon Argument - This fallacy is similar to ad populum except that it deals with actions rather than beliefs. Appeal to Authority - This fallacy occurs when an 'expert' on a subject is used in a claim. The fallacy occurs not in having the expert (which is perfectly valid) but in using their expertise to avoid critical examination. Appeal to False Authority - This fallacy occurs when the 'expert' has no credentials in the field of the argument. (ex. a sign i saw on a scientology-run shop "Tom Cruise says psychiatry is psuedo-science". However, Tom Cruise is not an authority on psychiatry nor science in general). Appeal to Anonymous Authority - This fallacy occurs when the source of evidence is not cited and is therefore unverifiable. It often appears as "studies show...", "scientists say..." or other vague reference. False Dichotomy - This fallacy occurs when only two options are presented (when many more are possible) and the arguer attempts to prove their case only through disproof of the opposition. Shifting Burden of Proof - The default position in any argument is the negative claim. It is the responsibility of the positive claimant to support their case. This fallacy occurs when the positive claimant tries to insert their position as the default for the opponent to then have to disprove. (eg. "you can't disprove god, therefore he does exist"). Special Pleading - This fallacy occurs when an arguer arbitrarily assumes an exception to a given rule. (eg. person 1 - "Everything has to have a cause, therefore the universe must have a cause. That cause is God" person 2 - "Then what caused God?" person 1 - "Nothing. God always was there.") Strawman Argument - This fallacy occurs when an oversimplification or false representation of the opponent's argument is set up. You then easily refute the constructed strawman, but have not addressed the substance of the opponent's position. Hasty Generalization - This fallacy occurs when you try to reach beyond the grasp of the evidence and draw a major conclusion from a minor subset of data. Non Sequitor (does not follow) - This fallacy occurs when the conclusion does not logically follow from the premises of the argument. Argument from Personal Incredulity - This fallacy occurs when one argues that because they don't believe something to be likely or true it therefore cannot be, irregardless of the evidence. Appeal to Ignorance - This fallacy occurs when a claim is assumed only due to the lack of an explanation existing. (eg. Science doesn't know how life began, therefore God did it). Equivocation - The misleading use of a term with more than one meaning depending on context. (eg 'theory' in science is 'a logically constructed model of a phenomenon that is well supported by evidence' but in common use it means more like 'conjecture'). Begging the Question (Circular Reasoning) - This fallacy occurs when the conclusion is assumed in one of the premises. the illusion of logic is created, but no real proof has been made. False Premise - In this fallacy, the conclusion is invalidated by an incorrect or assumptive premise. Ad Hoc Reasoning (For This Purpose) - Ad hoc reasoning is used to salvage a shaky foundation or false premise and is often used to avoid re-evaluation of the argument. Slippery Slope - A slippery slope argument states that accepting a certain argument will lead to a chain of events ending in an undesirable outcome. The validity of the argument is not addressed, only the imagined outcome. Confusing Correlation with Causation - This fallacy assumes that because two things show a correlation, one specifically caused the other. In reality, there's 4 possibilities. If a correlation exists between A and B, then: A causes B B causes A C causes A and B A and B are unrelated Shifting the Goalposts - When the rules for successfully achieving a goal are changed just as they are achieved. In this fallacy, the argument can never be proven to satisfaction. There are many more, but I'm getting tired so Ii'll continue this later. Constructing a good argument There is a great deal of debate over the internet - unfortunately, most arguments presented are very poorly developed. An argument, to quote a Monty Python sketch, is "a connected series of statements to establish a definite proposition." This occurs through 3 parts: premises, inferences, and the conclusion. We'll cover all 3 with examples here. Premise(s) - This is the foundation from which the rest of the argument is built upon. Premises must be explicitly and concisely stated. eg. Premise 1: a standard deck of playing cards consists of 4 suits - hearts, spades, clubs, diamonds. Premise 2: Each suit consists of 13 values. Inference - This is the development of new propositions from the premise(s) and are aften useful (but not always necessary) in building up to the conclusion. eg. We can determine the number of cards in a standard deck by multiplying suits and values. Conclusion - This is the final part of the argument in which the premises and inferences are used to draw a final point. eg. Therefore, a standard playing deck contains 52 cards. Now that the argument has been completely drawn, it's time to prepare it for presentation. This is often the hardest step as it involves a great deal of self-criticism. First, it should be examined for logical fallacies (I posted a common, albeit far from comprehensive, list here: http://forums.x10hosting.com/crossfire/95559-logical-fallacies.html ) As you are doing the self-examination, ask yourself the following questions: Are all my premises valid? (check sources, correct errors, make sure quotes are used in context, etc.) Are my assumptions minimal and acceptable? (Outside of mathematics, logical relations, and definitions, nothing is considered to achieve 100% certainty, and some degree of assumption will exist, but they should be as limited as possible.) Can I back up my claims with empirical, objective evidence? Does my conclusion logically follow from the evidence presented? After these self-checks, I often find it beneficial to attempt to refute my own arguments to see how strong they really are - if I can refute it then more likely than not so can others. Hopefully this brief tutorial will help everyone in composing quality arguments here and wherever else you may find the need.