Logical Fallacies Part Deux – GMAT edition
If you’ve read our blogs, you have probably read Lom’s article on logical fallacies. He does a great job listing out and explaining a lot of common fallacies. The thing is, there are quite a few of them. Just take a look at the wiki. I’m just going to interject here a bit to reduce and refine the list to one more suited to people who are looking to prepare for the GMAT or the GRE.
If you take a look at the wiki list of fallacies, it may seem overwhelming. But don’t fret, a lot of the individual fallacies listed are actually fundamentally similar. For instance, there are many appeal to emotion fallacies: based on fear, flattery, pity, etc. But basically they all rely on emotion. I take it further and lump all appeal based fallacies together. All of those are based on evidence that is not factual and/or is without relevance, hence the term Red Herring. Now that we know that we can group these ideas together, I’ll lay out the most useful ones.
Since we are not taking a formal logic class we are mostly talking about non-structural logical fallacies. Basically, what are called informal fallacies. These things involve understanding the content of the arguments. The major groups are Causal, Sampling, and Analogy issues, plus some other ones that don’t fit in those molds.
Causal flaws are perhaps most common. The big idea is whether you can say for certain something results from the given evidence. Here is an scenario to consider: “It’s a particularly hot summer on the lake. People are buying an unprecedented amount of shaved ice, and also are reporting a lot of water sports injuries.” All of these previous statements are facts, as in true. A reasoning question will take these facts and add a conclusion that sounds reasonable but is flawed. For instance, to make an obvious correlation error I could state that “when people buy a lot of shaved ice more accidents happen.” Or more subtly, high temperatures caused people to buy a lot of shaved ice. Basically, just because two things happen at the same time does not mean they are related. Both of those previous statements also have issues because the causation could be reversed or there could be other causes involved.
Sampling flaws are issues regarding representative sampling. As someone from the States, I am keenly aware of this trap right now. Polls do not always represent reality. Always ask yourself if a sample is representative. Even though they are not the same, I like to lump Statistical fallacies with Sampling. Basically differences in percentages do not necessarily mean similar differences in absolute numbers. For example, North Korea has the highest percentage of people in the military. Does it have the largest standing army? The answer is no.
Analogies flaws are pretty much the classic “apples and oranges” problem. How can you compare two things are that not the same? Better yet, how can you use one to support or detract from the other? Ok, example. China’s policies have led to incredible economic growth. Should other countries follow China’s policies? What works for China probably won’t work for anyone else.
These are just the major types of logical fallacies you can see in the GMAT. About a third of the Verbal questions are Critical Reasoning questions. On the GRE a few reasoning questions are hidden under Reading Comprehension. Not only then but these fallacies are also necessary to properly assess and write AWA essays. Regardless of what test you are going to take, you want to become familiar with the most common logical argumentation errors.