I watched a ridiculous commercial today. In it, customers sat in a salon and got their hair shampooed, but the stylists didn’t use any water. The result was a bunch of soapy messy customers. That was followed by this really ridiculous conclusion: You wouldn’t shampoo your hair without water, so why would you use toilet paper that didn’t have water in it.
I looked at my wife incredulously when I saw the ad because I couldn’t believe that the advertisers thought people would be stupid enough to look at that and nod along:
“Sure, water with shampoo makes sense, so why not water with toilet paper?”
However, the fact that this ad made it through several stages of review and made it to the air suggests to me that the advertisers do think that the public will go along with this. In order to make sure you’re not swept along, let’s take a look at the assumption present in this argument.
An argument’s general form is that there are premises—or pieces of evidence—that form the support for the final piece of an argument, the conclusion. Let’s take a look at this commercial in that form.
Shampooing with water is good + Shampooing without water is bad à Toilet paper with water is good
Now, I mentioned the two most important parts of the argument (conclusion and premises) but there is another piece that may be present. When the premises on their own do not conclusively establish the conclusion, the assumptions are the unstated pieces of evidence needed to get to the conclusion.
Some assumptions are probably safe. For instance, if I said I needed to deposit checks so I was going to the bank, it’s a good bet that I’m going to a financial institution rather than a food bank or a phone bank. However, the gap between the premises and the evidence leaves some room for doubt, and so that is an assumption we’re making. Identifying assumptions is a key skill on the GMAT, because you won’t be asked to judge how valid an assumption is, merely whether or not it is present.
In this case, the commercial makes a common form of assumption called argumentation by analogy. In order to go along with the argument presented in the commercial, we have to believe that the subject of the evidence and the subject of the conclusion are similar enough that what’s true of one will also be true of the other. Let’s take another look at the argument with that assumption added in:
Shampooing with water is good + Shampooing without water is bad + (What’s good for shampooing is also good for toilet paper) à Toilet paper with water is good
With that link added, this argument is now logically sound. However, if you don’t believe this assumption you probably won’t be convinced that buying this brand of toilet paper is the best.
Keep the idea of assumptions in mind and look out for argumentation by analogy both on the test and on TV. If you can spot those assumptions well you’ll pick up some points and avoid the tricks of advertisers.