By Jim Wilson:
In a structurally valid argument, if all the premises are true, the conclusion will be true. A logical fallacy occurs when the argument is not structurally valid and the truth of the conclusion has no relationship to the premises that it is built upon. In short, logical fallacies are bad arguments. Everyone should learn to recognize them and point them out when they see them. There are many lists of logical fallacies on the internet and a quick search provides plenty of information but sometimes it is good to review them. These should be taught to students at a very young age. There are many fallacies out there that are closely related. Here are some of the common ones:
1. Argument from Authority: The claim that if a knowledgeable/respected/trusted individual holds a position, the position must be true. Example: “The Pope claims that birth control is sinful, therefore it must be sinful.” Note there are often cases where an authority has knowledge of a given topic but their acceptance of the position should not be taken as evidence that the position is true. Sometimes highly knowledgeable people are wrong about things within their area of expertise and often knowledgeable people will disagree with each other within their own areas of expertise.
2. Ad Hominem: Attacking the argument by attacking the person making it. Example: “John’s position is wrong because he is a communist/capitalist/jerk/close-minded etc.” Sometimes jerks make logically valid arguments. Rather than call the person making the argument names, one should always address the argument itself.
3. Argument Ad Populum: The argument that just because a position is popular makes it correct. This is a close relative of the argument from authority. Example: “Could 20 million Justin Bieber fans be wrong?” Yes. It was once widely believed that the Earth is flat and the center of the universe and that disease was caused by demons. Just because an idea is popular does not mean it is correct.
4. Argument from Antiquity: The argument that because an idea has been around for a long times it must be correct. Very closely related to the argument from tradition which states because we have been doing things this way for a long time, it must be the correct way of doing it. Example: “Because the Koran has been used as a source of wisdom for generations, it must be profound.” Contrast this with the argument from novelty: the idea that because an idea is new or unique it must be correct.
5. Begging the question: Assuming one’s unproven conclusion, when presenting a premise or question. Examples: “Do your parents know you are gay? Are you still beating your wife? Why are atheists angry? Who created the universe?” All of these questions smuggle in unfounded assumptions: that the person spoken to is gay, they beat their wife, atheists are angry, and that someone created the universe. This fallacy should not be confused with raising the question, as the phrase “that begs the question” is often used to imply.
6. Straw Man: An attempt to counter an argument, by attacking a different, usually weaker and superficially similar argument, instead. For an example we turn to this quote from Ray Comfort on evolution: “There is a big bang, life forms, and after millions of years a dog evolves. It is the first dog. He has got legs, tail, teeth, eyes – and it’s good he has good he has eyes because he has to look for a female, he has been blind for millions of years but now he can see. He has got to find a female. She has got to be evolved at the right place at the right time with all the reproductive organs and a desire to mate. “
In reality no evolutionary biologist argue that evolution occurs within entire populations and such features as legs, eyes and teeth would have long developed within mammals long before they diversified into the subset known as dogs.
7. Tu Quoque: This means “you too.” This appeal to hypocrisy meant to turn any criticism against the accuser. Example: “Atheism requires faith like Christianity does.” This would imply that both positions must then be equally valid. In reality, it does not require faith to be an Atheist.
8. Naturalistic Fallacy: The argument that because something is natural or from nature it must be good for people. For example: Organic Foods must be better for you because they are natural. Note rattlesnake venom and arsenic are also natural.
9. False Dichotomy: When only two alternatives are presented and there are in fact others that are not mentioned. For example: “Jesus performed miracles so he must have had divine powers or been a con man”. There are other alternatives. Maybe he did not really perform miracles and miracles are elements of his story that were added after his death. Maybe he didn’t really perform miracles but was convinced he could and was able to convince other he could as well.
10. Fallacy Fallacy: The assumption that because someone’s argument is fallacious their conclusion must be incorrect. It’s possible for someone to argue for a correct conclusion but in doing so suffers an inadvertent logical fallacy. For example I cannot reject the conclusion that nothing is wrong with homosexuality solely because someone has attempted to argue using a naturalistic fallacy, I would be committing the fallacy fallacy. There is nothing morally wrong about homosexuality, but that cannot be demonstrated by arguing that it is natural.
You are likely to come across these common fallacies. There are many more.