Slippery slope

Sponsorship the way you would do it

Slippery slope, also known as the thin end of the wedge or the camel's nose, refers both to an argument about the likelihood of one event given another, and to a fallacy about the inevitability of one event given another. Slippery slope means predicting without justification that one step in a process will lead unavoidably to a second, generally undesirable step.

Table of contents

1 Argument
2 Fallacy
3 Semantic forms of slippery slope
4 External Links

Argument

The argument occurs in the following context: A, B denote events, situations, policies, actions etc. Within this context, the following inferential scheme is posited:

If A occurs

B is more likely to occur

The argument takes on one of various semantical forms. In one form, it is that argued by making a move in a particular direction, we are starting down a "slippery slope" in which it is likely that we will continue in the same direction (usually deemed by the arguer to be a negative one; hence the "sliding downwards" metaphor). The other form is more static arguing that admitting or permitting A leads to admitting or permitting B, by following a long chain of logical relationships.

An example is the argument by many civil libertarians that even minor increases in government authority make future increases more likely, by making them seem less noteworthy: what would once have been considered a huge power grab, the argument goes, is now seen as just another incremental increase, and thus is more palatable (see, e.g. [1]).

Eugene Volokh's Mechanisms of the Slippery Slope (PDF) analyzes various types of such slippage. Volokh uses the example "gun registration may lead to gun confiscation" to describe five types of slippage:

Cost-lowering: Once all guns are registered, the government will know exactly who to confiscate them from.
Legal rule combination: Previously the government might need to search every house to confiscate guns, and such a search would violate the Fourth Amendment of the Constitution of the United States. Registration would eliminate that problem.
Attitude altering: People may begin to think of gun ownership as a privilege not a right, and thus think of gun confiscation not as seriously.
Small change tolerance: People may ignore gun registration because it's a small change, but when combined with other small changes, it could lead to the equivalent of confiscation.
Political power: The hassle of registration may reduce the number of gun owners, and thus the political power of the gun ownership bloc.
Political momentum: Once this gun law is passed it becomes easier to pass other gun laws, including laws like confiscation.

Fallacy

The slippery slope argument may or may not be fallacious. See the discussion on the two interpretative paradigms below: the momentum paradigm and the inductive paradigm. However the slippery slope claim requires independent justification to connect the inevitability of B to an occurrence of A. Otherwise the slippery slope scheme is a device of sophistry. Often a long series of intermediate events leading from A to B is proposed as the mechanism of connection. The "camel's nose" is one example: once a camel has managed to place its nose within a tent, the rest of the camel will inevitably follow. In this sense the slippery slope is like the genetic fallacy but in reverse.

The slippery slope fallacy is also often connected to the straw man fallacy to attack the initial position:

A has occurred (or will or might occur); therefore
B will inevitably happen. (slippery slope)
B is wrong; therefore
A is wrong. (straw man)

This form of argument is often used to provide evaluative judgements on social change: Once an exception is made to some rule, there will be nothing holding back further, more egregious exceptions to that rule.

Note that these arguments may indeed be valid, but some independent justification of the connection must be provided, otherwise the argument is fallacious.

It can also be related to the conjunction fallacy: with a long string of steps leading to an undesirable conclusion, all actually occurring is actually less likely than any individual step alone.

Contemporary examples of the slippery slope fallacy may include:

If we allow women to abort their unborn children, then soon no life will be held sacred.
If we forbid partial-birth abortion, soon all abortion will become illegal.
If we allow guns to be registered, then gun confiscation will follow.
Use of 'soft' drugs such as cannabis will inevitably lead to addiction to 'harder' drugs such as heroin.
If we allow gay marriage, the whole institution of marriage will break down and collapse

Semantic forms of slippery slope

There are at least two forms of semantics for the slippery argument which we now discuss: The momentum semantics and the induction semantics.

Momentum:

In the momentum interpretation, the occurrence of event A will initiate a process which will lead inevitably to occurrence of event B. The process may involve causal relationships between intermediate events, but in any case the slippery slope schema depends for its soundness on the validity of some analogue for the physical principle of momentum. This often takes the form of a domino theory or contagion formulation. The domino theory principle may indeed explain why a chain of dominos collapses, but an independent argument is necessary to explain why a similar principle would hold in other circumstances. One way to achieve this is to establish an abstract model for the terms that occur in the argument, in which the momentum principle obtains. This leaves showing the validity of the abstract model as a separate intellectual exercise.

Induction:

The other interpretation resembles mathematical induction. Consider the context of making evaluative (or accessibility) judgements (good or bad, permit or deny) on each one of a class of events or situations. Assume these events can be arranged in an infinite sequence

A₁, A₂, A₃.., A_k,..

such that for each k, event A_k differs from A_k+1 in a uniform way and the difference between events A₂ and A₁ is small.

Moreover, the following evaluations are given:

A_n is considered harmful for some large value of n.

By uniformity, it follows that the difference between A_k+1 and A_k for k=1,2,3, ... is small. In particular, A_k+1 should receive the same evaluation as A_k. Therefore by iterating this process we deduce

For any k=1,2,3,..., A_k should have the same evaluation as A₁.
Therefore A₁ should be considered harmful.

For example, the following arguments fit the slippery slope scheme with the inductive interpretation

If we grant a building permit to build a Mosque (Pentecostal Church, Temple) in our community, then there will be no bound on the number of building permits we will have to grant for Mosques (Pentecostal Churches, Temples) and the nature of this city will change. This argument instantiates the slippery slope scheme as follows: A_k is the situation in which k building permits are issued. One first argues that going from the situation of k permits issued to k+1 permits issued is no different than from going from 1 to 2. One such argument could run as follows: for arbitrary k>1, we are adding a Mosque (Pentecostal Church, Temple) in an environment where at least one already exists which is similar to the case k=1. Moreover, issuing permits to build 1000 Mosques (Pentecostal Churches, Temples) in a city of 300,000 will clearly change the nature of the community.
If we allow use of Spanish in this special class for immigrants, then there is no limit to the number of classes where we allow usage of Spanish.

The soundness of the argument can only be evaluated by appropriately formulating the semantics of the slippery slope scheme. In the naive presentation as an instance of mathematical induction it is clear that the argument is indeed sound. However, in most real-world applications, including the two given above this naive semantics fails because the inductive scheme fails for imprecisely defined predicates.