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English 102
Syllabus (DOC file)
Davis Oldham
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I think the simplest way to assess reasoning is by looking at premises. Identifying fallacies is another popular method. And a third is by evaluating the evidence. In this document I describe a couple common fallacies and relate them to the idea of premises.
Fallacies are mistakes in the process of reasoning. You can think of them as breaking the rules on how to move from the stated premises to the conclusion.
Here’s one example:
All men are mortal.
Socrates is mortal.
Therefore, Socrates is a man.
In fact, there are lots of other things besides men that are mortal—women, children, jellyfish, cacti, etc. For all we know, Socrates could be a dog. Just because Socrates is mortal doesn’t mean that he must be a man. The syllogism is invalid, because you can’t get from the stated premise to the conclusion.
People have made huge lists of different types of fallacies. It’s a popular topic on the web (try searching for “common logical fallacies”). You can find some of the more common at the University of North Carolina’s Fallacies page. I recommend that you look over this list to get familiar with some of the most common fallacies. It can help you explain why something doesn’t add up. It’s also good mental training, and will help you recognize all sorts of flaws in reasoning, whether it’s your friend’s argument about why one team is better than another or a politician’s effort to get you to vote for them.
A much more in-depth discussion and list can be found on in the article on Fallacies from the Internet Encyclopedia of Philosophy or IEP.
Another good resource, though quite technical, is the Stanford University Encyclopedia of Philosophy. Here is their section on fallacies.)
Here I will talk about the example above in terms of the hidden assumptions or premises it depends on. In the next section I will try to show how you might use the idea of fallacy to critique the assigned reading.
The fallacy shown above, about Socrates, is an example of a well-known error in reasoning called “Affirming the Consequent,” which the IEP describes here. The basic idea is that you have a statement that might be true (Socrates is a man), one that is true for sure (Socrates is mortal) and one that connects them (if he were a man he would be mortal). The fallacy reverses that connection (if he were a mortal he would be a man).
I said above that a fallacy is an error in moving from the stated premise to the conclusion. Almost always in these cases it turns out there’s another, unstated premise which is the real basis for the argument. This hidden assumption is usually mistaken in some way.
In the example given above, the hidden assumption or premise is this:
All mortals are men—in other words, if he were a mortal he would be a man.
Once we’ve identified this premise, we can see two things very clearly:
As I said, I think most fallacies can be more easily analyzed this way. It saves the trouble of having to memorize the names of lots of different fallacies, and instead just remember one simple rule:
Expose all hidden premises!
Imagine a company is trying to convince you their product is the best ever. They give you a list of great things about the product in order to show you why it’s the best. This might seem convincing at first glance. But most people will recognize that there is more to the story. What about the negatives—the things the product can’t do, its weaknesses and limitations?
So, although the company has given lots of evidence in support of their claim, some would argue that they are ignoring the evidence on the other side of the issue. The UNC Fallacies page calls this the fallacy of hasty generalization. It is also sometimes referred to as suppressed evidence, special pleading or card stacking.
Remember I said that a fallacy is an error in moving from the stated premise to the conclusion. In this example, the stated premises are all about the product’s strengths. There are none about its weaknesses. If you find an article’s reasoning fallacious, it may be because you think that the stated premises by themselves don’t add up to the conclusion.
Here, too, though, there seems to be an unstated premise. It might be this:
The product’s limitations are insignificant compared to its strengths, and therefore can be ignored.
Of course, the fact that it’s unstated means it’s not always clear what, exactly, the assumption is. Another possible unstated premise for this claim might be this:
The product’s limitations are already well known, and therefore need not be described.
It might even be that the author is assuming both things! Your job as reader is to try to figure out what is the most likely interpretation of the unstated premise. Once you’ve done that, you can decide if you think it is reasonable or not.
It’s good practice to learn to recognize different types of fallacies. But if you find there are too many to keep track of, you can simplify matters by going back to the idea of assumptions. One way or another, all fallacies can be explained in terms of unstated premises.