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I'm having trouble understanding how this is not a valid argument.

It says that some classes of animals are so successful that they are widespread, while others are not and are thereby threatened. It says that insects are the former sort (thus, an insect is one of the "class of animals that is so successful that are widespread") and then that ants are the most successful of these. It concludes that no species of ants are threatened.

My thinking is this: If insects are a class of animal that are so successful that they are widespread, then wouldn't all animals in this class (such as ants) be so successful that they are widespread? The stimulus seems to imply that the entire class has this characteristic ("so successful that they are widespread") and thus wouldn't it be correct to say that all members of this class (ants, species of ant) have this characteristic? Otherwise we would have to say that those species of ants are not insects... right? An ant species can be LESS successful than other ant species, but it doesn't seem to me that it can be so not successful as to be threatened.

Simply put, a characteristic of a group is not necessarily a characteristic its members; vice versa.

Let's say America is the wealthiest country. Does that mean each person in America is wealthier than each person in every other country? Not necessarily. (I'm sure some duke in England is wealthier than I am. Does that mean England is wealthier than America? Not necessarily.) Arguments that commit the fallacy say, "Yes, necessarily."

pricon wrote:Simply put, a characteristic of a group is not necessarily a characteristic its members; vice versa.

Let's say America is the wealthiest country. Does that mean each person in America is wealthier than each person in every other country? Not necessarily. (I'm sure some duke in England is wealthier than I am. Does that mean England is wealthier than America? Not necessarily.) Arguments that commit the fallacy say, "Yes, necessarily."

That doesn't seem to be what the argument is saying though. The way it is built -- i.e.: insects are the of the class of insects that are "so successful that they appear everywhere" seems to say that all insects are so successful that they appear everywhere. If all insects are in that class, and that insect "class" is "so successful," how can that mean that all species that are in that class are not "so successful?" The argument almost makes it so that "so successful" is an inherent trait of insects.

Mammals are a class. Let's say mammals are indigenous to every continent (true). Now let's say that, therefore, the species homo sapien must be indigenous to every continent (false).

As you can see, based on our common knowledge, we know that there is some logical fallacy there. Now memorize that fallacy and use it in new situations, whether or not you know the truth behind them.

pricon wrote:Mammals are a class. Let's say mammals are indigenous to every continent (true). Now let's say that, therefore, the species homo sapien must be indigenous to every continent (false).

As you can see, based on our common knowledge, we know that there is some logical fallacy there. Now memorize that fallacy and use it in new situations, whether or not you know the truth behind them.

Thanks man -- super intuitive when you put it that way. I almost never miss whole-to-part flaws, so it is strange that this one gave me so much trouble.

Glad I could help!