Slippery slope

Slippery slope

In debate or rhetoric, the slippery slope is one of the classical informal fallacies. It suggests that an action will initiate a chain of events culminating in an undesirable event later without establishing or quantifying the relevant contingencies. The argument is sometimes referred to as the thin end of the wedge or the camel's nose. In broader, especially recent, pragmatic usage, the term slippery slope argument alternately refers to a non-fallacious argument that such undesirable events are rendered more probable. The fallacious sense of "slippery slope" is often used synonymous with continuum fallacy, in that it assumes there is no gray area and there must be a definite transition at a certain point from category A to category B.

While the general form of the argument involving a slippery slope is not valid, the conclusion it leads to is not necessarily wrong.

Slippery slope arguments

The argument takes on one of various semantical forms:
* In one form, the proposer suggests that by making a move in a particular direction, we start down a "slippery slope". Having started down the metaphorical slope, it appears likely that we will continue in the same direction (the arguer usually sees the direction as a negative direction; hence the "sliding downwards" metaphor).
* Another form appears more static, arguing that admitting or permitting A creates a precedent that leads to admitting or permitting B, by following a long chain of logical relationships. Note that establishing this chain of logical necessity (or quantifying the relevant probabilities) makes this a valid argument and thus not a slippery slope according to the classical definition. The slippery slope is not a fallacy by virtue of a chain of implications (which relies on the transitivity of the material conditional) but rather because of the failure to factually establish said chain.


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

# Cost-lowering: Once all gun-owners have registered their firearms, the government will know exactly from whom to confiscate them.
# 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 rather than a right, and thus regard gun confiscation less seriously.
# Small change tolerance: People may ignore gun registration because it constitutes just 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 the government has passed this gun law it becomes easier to pass other gun laws, including laws like confiscation.

Slippery slope can also be used as a retort to the establishment of arbitrary boundaries or limitations. For example, one might argue that rent prices must be kept to $1,000 or less a month to be affordable to tenants in an area of a city. A retort invoking the slippery slope could go in two different directions:
* Once such price ceilings become accepted, they could be slowly lowered, eventually driving out the landlords and worsening the problem.
* If a $1,000 monthly rent is affordable, why isn't $1,025 or $1,050? By lumping the tenants into one abstract entity, the argument renders itself vulnerable to a slippery slope argument. A more careful argument in favor of price ceilings would statistically characterize the number of tenants who can afford housing at various levels based on income and choose a ceiling that achieves a specific goal, such as housing 80% of the working families in the area.

A very common political "slippery slope" is negotiating with terrorists. The argument is that if governments negotiate with terrorists, then the government acknowledges that terrorist groups have power, terrorism will be seen as a method that produces results and therefore terrorism will become more prevalent as a means to gain power and force governments to concede to demands. This argument is reasonable, but to be valid it must be backed up with supporting evidence relating to the premises made. Similarly, judiciary decisions must be considered in terms of the consequences of the legal precedents they set, and foreign policy decisions in terms of their effect on credibility.

The slippery slope as fallacy

The heart of the slippery slope fallacy lies in abusing the intuitively appreciable transitivity of implication, claiming that A lead to B, B leads to C, C leads to D and so on, until one finally claims that A leads to Z. While this is formally valid when the premises are taken as a given, each of those contingencies needs to be factually established before the relevant conclusion can be drawn. Slippery slopes occur when this is not done -- an argument that supports the relevant premises is not fallacious and thus isn't a slippery slope in technical definition of the term.

Often proponents of a "slippery slope" contention propose a long series of intermediate events as the mechanism of connection leading from A to B. The "camel's nose" provides one example of this: 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 resembles the genetic fallacy, but in reverse.

As an example of how an appealing slippery slope argument can be unsound, suppose that whenever a tree falls down, it has a 95% chance of knocking over another tree. We might conclude that soon a great many trees would fall, but this is not the case. There is a 5% chance that no more trees will fall, a 4.75% chance that exactly one more tree will fall (and thus a 9.75% chance of 1 or less additional trees falling), and so on. There is a 92.3% chance that 50 or fewer additional trees will fall. The expected value of trees that will fall is 20. In the absence of some momentum factor that makes later trees more likely to fall than earlier ones, this "domino effect" approaches zero probability.

Arguers also often link the slippery slope fallacy to the straw man fallacy in order 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 often provides evaluative judgments on social change: once an exception is made to some rule, nothing will hold back further, more egregious exceptions to that rule.

Note that these arguments may indeed have validity, but they require some independent justification of the connection between their terms: otherwise the argument (as a logical tool) remains fallacious.

The "slippery slope" approach may also relate to the conjunction fallacy: with a long string of steps leading to an undesirable conclusion, the chance of all the steps actually occurring is actually less than the chance of any one of the individual steps occurring alone.

Supporting analogies

Several common analogies support slippery slope arguments. Among these are analogies to physical momentum, to frictional forces and to mathematical induction.

Momentum or frictional analogies

In the momentum analogy, 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 may take 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.

An analogy similar to the momentum analogy is based on friction. In physics, the static co-efficient of friction is always greater than the kinetic co-efficient, meaning that it takes more force to make an object start sliding than to keep it sliding. Arguments that use this analogy assume that people's habits or inhibitions act in the same way. If a particular rule A is considered inviolable, some force akin to static friction is regarded as maintaining the status quo, preventing movement in the direction of abrogating A. If, on the other hand, an exception is made to A, the countervailing resistive force is akin to the weaker kinetic frictional force. Validity of this analogy requires an argument showing that the initial changes actually make further change in the direction of abrogating A easier.

Induction analogy

Another analogy resembles mathematical induction. Consider the context of evaluating each one of a class of events A1, A2, A3,..., A"n" (for example, is the occurrence of the event harmful or not?). We assume that for each "k", the event A"k" is similar to A"k"+1, so that A"k" has the same evaluation as A"k"+1.

Therefore A"n" has the same evaluation as A'1.

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

* "If we grant a building permit to build a Mosque (or Church, or Temple) in our community, then there will be no bound on the number of building permits we will have to grant for Mosques (or Churches, or 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 the situation of "k" permits is not significantly different from the one with "k" + 1 permits. Moreover, issuing permits to build 1000 Mosques (or Churches, or Temples) in a city of 300,000 will clearly change the nature of the community.

In most real-world applications such as the one above, the naïve inductive analogy is flawed because mathematical induction cannot be applied to imprecisely defined predicates.

ee also

*Legal precedent
*Foot-in-the-door technique
*Reductio ad absurdum
*The camel's nose
*Domino theory


* Mario Rizzo and Glen Whitman. [ "The Camel's Nose is in the Tent: Rules, Theories and Slippery Slopes"] , UCLA Law Review 51.2 (2003): 539-592.

External links

* [ Propaganda Critic: Unwarranted extrapolation]
* [ Nizkor: Slippery slope]
* [ Fallacy files: slippery slope]
* [ Slippery slope in politics]

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