What is a slippery slope in ethics

What's so deceptive about Slippery Slope Fallacy?

According to the Fallacy Files, a slippery slope argument is an example of an informal fallacy:

A formal error is one that is not formal, that is, it is a type of error in which the content of the argument is relevant to its error or which is deceptive for epistemological, dialectical, or pragmatic reasons. As a rule, informal errors occur in nondeductive thinking, which relies on both the content and the form of coherence. Since content is important in the case of informal errors, there are also arguments for the form of the error that are compelling. For this reason, forms for informal errors are only used for identification purposes, ie one cannot tell from the form alone that an instance is deceptive. Rather, the forms will help to distinguish between different species to distinguish informal error.

In other words, just because someone is making an argument in shape Used on a slippery slope, it does not mean that its argument is invalid or deceptive. It is entirely possible to construct a slippery hang argument that works and is convincing:

Don't light that cigarette or the next one that you know you have lung cancer!

It works because smoking is addicting (once you start it is difficult to quit) and it causes different types of cancer. Obviously won't all People who start smoking develop lung cancer, and some people with lung cancer have never smoked. But that is not what the argument claims. Rather, it tries to convince the listener that making a particular choice (smoking) may have unintended consequences that are beyond their control (getting cancer).

A similar argument is deceptive:

Don't go to that dance or the next one that you know you are pregnant!

This it does not work (even if the listener is female) as there are many things a person can do to avoid getting pregnant in a dance. 1 For example, a dancer may say "no" to a possible connection or use contraception. The argument does not stop if subsequent decisions can be made to prevent a person from sliding onto the (presumably) undesirable bottom of the slope.

There's a closely related argument sometimes called a semantically slippery slope. Instead of having the form "X leads to Y, which leads to Z", it says "X is like Y, which is like Z". This version depends on the indeterminacy of the lines between X and Y and Z. We see this type of reasoning a lot in the abortion debate:

Killing a baby after birth is wrong, therefore killing a fetus after 9 months is wrong, therefore killing a fetus after 8 months is wrong ...


A fetus is just a mass of cells in a woman's body, so removing these cells has the same ethical complications as removing [another mass of cells].

Neither of these arguments hold up on their own, as reasonable people can draw clear lines between one situation and another. Is a fetus a part of the woman's body or an independent human? The lines are fuzzy so it depends on where you start. Neither argument is particularly convincing to people who make different assumptions or have different ethical priorities.

A semantic argument for a slippery slope might be compelling, but it's also a red flag that something might be wrong beneath the surface.


1. The old joke: A Baptist minister once warned young people against sex because it made them dance.


The fetus example is actually interesting because it is not necessarily deceptive in and of itself. After all, brains are also masses of cells, but removing the brain from a living person is not very ethical.