Informal Fallacies

Informal Fallacies

An argument contains an informal fallacy when at least one of its premises don't support its conclusion. You can also think of this in terms of internal relevance: one or more of the premises isn't relevant to the conclusion. Most informal fallacies are the result of a hidden premise/assumption being irrelevant to the conclusion. A good way to figure out if an argument contains an informal fallacy is to formalize the argument and make explicit the hidden assumption. For example, a very common fallacy is the naturalistic fallacy. You'll often hear something like this: You should eat product A because it's all-natural. When we formalize the argument and reveal the hidden assumption we can easily see why it's a bad argument:

P1. Product A is all-natural.
HP2*. If something is all-natural then it's good and you should eat it.
C. You should eat product A.

HP=Hidden premise/assumption

HP2 is false. Just because something is all-natural doesn't necessarily mean it's good for you (or that it's good to eat). Some natural things are very bad for you. For example, snake venom and arsenic are both all-natural but it doesn't follow that they're good for you and that you should eat them! Often the name of the fallacy has to do with the hidden premise in the argument. In this case it's the naturalistic fallacy which is the false premise that if something is natural then we can deduce that it's good for you.

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