A slippery slope is a type of informal fallacy that arises when the arguer claims that a chain of causal events will necessarily occur. Hence, a slippery slope is committed when a person argues that some event or practice he or she disapproves of will trigger a sequence of events that will ultimately lead to some undesirable consequences. The reasoning here is that since we do not want the undesirable consequence, we ought therefore to oppose the initial event or practice. The fallacy in the reasoning consists in the false assumption that the chain of events will in fact occur.
Let us consider the example below.
Example 1
You have all heard of grade inflation. Well, I want to speak to you about grade depression: the serious harm we do to students by grading them too hard rather than too easily. What does it do to students to measure them by too strict a standard? It frustrates them. It conditions them to expect failure. They recoil from responsibility, always taking the easy route rather than learning to challenge and, hence, improve themselves. They develop a habit of dependency, and many develop the symptoms of neurosis and other psychological disorders. Can we afford a generation of weak, dependent people unsuited for the demands of contemporary society?
As we can see in the example above, the arguer opposes a strict grading policy by claiming that it will ultimately lead to a generation of weak, dependent people. The first stage in the causal chain, that is, strict grading leads to frustrations, is perhaps reasonable. But from that point on, the series of events is unlikely. As a matter of fact, there is no good reason to believe that harsh grading will lead to an expectation of failures, withdrawal from responsibility, and eventually dependency and neurosis. For this reason, the arguer in the example above commits the fallacy of slippery slope.
Again, the slippery slope fallacy is committed when we accept without further justification or argument that once the first stage in the causal chain is taken, the others are going to follow.
It is important to note that there is another form of a slippery slope fallacy, which occurs when it is assumed without warrant that slight differences or differences of degrees are unimportant. Let us consider the example below.
Example 2
There is no point in sending money to aid starving children in Haiti because there are also starving children in West Papua, and it would be unjust not to aid them as well.
If we analyze the example above, it says that there is no need for us to help the starving children in Haiti because this action cannot make a difference. After all, there are countless starving children around the world, especially in West Papua. Moreover, the example above says that it would be unjust on the part of the starving children in West Papua if we only send aid money to the starving children in Haiti. Hence, the argument says that if we send aid money to the starving children in Haiti, then we need to send aid money as well to all starving children around the world. Again, when this argument occurs, a fallacy of slippery slope is committed.