A slippery slope is a type of argument that is usually a logical fallacy. A slippery slope argument suggests a series of causal events that lead to a bad outcome when there is no evidence that one event will cause the others. It’s an argument that if A happens then B will occur which will lead to C and D and then E and E is a really bad outcome.
The reason a slippery slope argument is usually a fallacy is that “It’s hard enough to prove one thing is happening or has happened; it’s even harder to prove a whole series of events will happen. That’s a claim about the future, and we haven’t arrived there yet. We, generally, don’t know the future with that kind of certainty. The slippery slope fallacy slides right over that difficulty by assuming that chain of future events without really proving their likelihood.” Source.
- If my state legalizes marijuana it will lead to legalizing other drugs like cocaine and heroin and we’ll end up with a society of drug users and stoners.
- If gay marriage is legalized it will lead to polygamy and marrying our pets and then marriage will have no meaning at all.
- If I don’t get into my desired college I won’t get a good job when I graduate and I’ll end up with a dead-end career and I’ll never be happy.
A slippery slope fallacy has three main features (source):
- A start that seems mild
- An endpoint that is significant or extreme
- A series of small steps that connect one to the other
Of course, not all causal series of events are a slippery slope. Sometimes a chain of events is perfectly plausible, such as: “if I keep eating fast food three times a day I’ll gain weight, my health will suffer, I’ll feel worse and years will be taken off my life.”
What to do: Like most logical fallacies, the best defense is to keep an eye out for when a slippery slope argument is used. In reality, there is nearly always enough friction on the slope that we can stop whenever we choose.
Related IFOD on Red Herring Fallacy