Chapter 4: Informal fallacies: Slippery Slope Fallacies

7. Slippery Slope Fallacies

Slippery slope fallacies depend on the concept of vagueness. When a concept or claim is vague, it means that we don’t know precisely what claim is being made, or what the boundaries of the concept are. The classic example used to illustrate vagueness is the “sorites paradox.” The term “sorites” is the Greek term for “heap” and the paradox comes from ancient Greek philosophy. Here is the paradox. I will give you two claims that each sound very plausible, but in fact lead to a paradox. Here are the two claims:

One grain of sand is not a heap of sand.
If I start with something that is not a heap of sand, then adding one grain of sand to that will not create a heap of sand.

For example, two grains of sand is not a heap, thus (by the second claim) neither is three grains of sand. But since three grains of sand is not a heap then (by the second claim again) neither is four grains of sand. You can probably see where this is going. By continuing to add one grain of sand over and over, I will eventually end up with something that is clearly a heap of sand, but that won’t be counted as a heap of sand if we accept both claims 1 and 2 above.

Philosophers continue to argue and debate about how to resolve the sorites paradox, but the point for us is just to illustrate the concept of vagueness. The concept “heap” is a vague concept in this example. But so are so many other concepts, such a color concepts (red, yellow, green, etc.), moral concepts (right, wrong, good, bad), and just about any other concept you can think of. The one domain that seems to be unaffected by vagueness is mathematical and logical concepts. There are two fallacies related to vagueness: the causal slippery slope and the conceptual slippery slope. We’ll cover the conceptual slippery slope first since it relates most closely to the concept of vagueness I’ve explained above.

Here is another example of a slippery slope argument:

Removing parking spaces will reduce car traffic on the road which will be bad for business.

This is a slippery slope argument because the logical (causal) connection between doing the action of removing car traffic and decreasing store visitors is too vague. The speaker just has to make up a consequence that would supposedly derive from the main claim even though there is no logical connection between the two. In this case, people can still visit stores by foot, public transit, etc..