Slippery slope
Encyclopedia
In debate
or rhetoric
, a slippery slope (also known as thin edge of the wedge, or the camel's nose
) is a classic form of argument, arguably an informal fallacy
. A slippery slope argument states that a relatively small first step leads to a chain of related events culminating in some significant effect, much like an object given a small push over the edge of a slope sliding all the way to the bottom. The strength of such an argument depends on the warrant, i.e. whether or not one can demonstrate a process which leads to the significant effect. The fallacious sense of "slippery slope" is often used synonymously with continuum fallacy
, in that it ignores the possibility of middle ground and assumes a discrete transition from category A to category B. Modern usage avoids the fallacy by acknowledging the possibility of this middle ground.
'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:
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:
Sometimes a single action does indeed induce similar latter action. For example, judiciary decisions may set legal precedents.
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 amount of trees would fall; however 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 fewer 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.
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 in sequence is less than the chance of any one of the individual steps occurring alone.
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.
. Consider the context of evaluating each one of a class of events A1, A2, A3,..., An (for example, is the occurrence of the event harmful or not?). We assume that for each k, the event Ak is similar to Ak+1, so that Ak has the same evaluation as Ak+1.
Therefore every An has the same evaluation as A1.
For example, the following arguments fit the slippery slope scheme with the inductive interpretation
In most real-world applications such as the one above, the naïve inductive analogy is flawed because each building permit will not be evaluated the same way (for example, the more religious structures in a community, the less likely a permit will be granted for another).
Debate
Debate or debating is a method of interactive and representational argument. Debate is a broader form of argument than logical argument, which only examines consistency from axiom, and factual argument, which only examines what is or isn't the case or rhetoric which is a technique of persuasion...
or rhetoric
Rhetoric
Rhetoric is the art of discourse, an art that aims to improve the facility of speakers or writers who attempt to inform, persuade, or motivate particular audiences in specific situations. As a subject of formal study and a productive civic practice, rhetoric has played a central role in the Western...
, a slippery slope (also known as thin edge of the wedge, or the camel's nose
Camel's nose
The camel's nose is a metaphor for a situation where permitting some small undesirable situation will allow gradual and unavoidable worsening. A typical usage is this, from U.S. Senator Barry Goldwater in 1958:...
) is a classic form of argument, arguably an informal fallacy
Informal fallacy
An informal fallacy is an argument whose stated premises fail to support their proposed conclusion. The deviation in an informal fallacy often stems from a flaw in the path of reasoning that links the premises to the conclusion...
. A slippery slope argument states that a relatively small first step leads to a chain of related events culminating in some significant effect, much like an object given a small push over the edge of a slope sliding all the way to the bottom. The strength of such an argument depends on the warrant, i.e. whether or not one can demonstrate a process which leads to the significant effect. The fallacious sense of "slippery slope" is often used synonymously with continuum fallacy
Continuum fallacy
The continuum fallacy is an informal logical fallacy closely related to the sorites paradox, or paradox of the heap...
, in that it ignores the possibility of middle ground and assumes a discrete transition from category A to category B. Modern usage avoids the fallacy by acknowledging the possibility of this middle ground.
Description
The argument takes on one of various semantical forms:- In the classical form, the arguer suggests that making a move in a particular direction starts something on a path down a "slippery slope". Having started down the metaphorical slope, it will continue to slide in the same direction (the arguer usually sees the direction as a negative direction, hence the "sliding downwards" metaphorMetaphorA metaphor is a literary figure of speech that uses an image, story or tangible thing to represent a less tangible thing or some intangible quality or idea; e.g., "Her eyes were glistening jewels." Metaphor may also be used for any rhetorical figures of speech that achieve their effects via...
). - Modern usage includes a logically valid form, in which a minor action causes a significant impact through a long chain of logical relationships. Note that establishing this chain of logical implication (or quantifying the relevant probabilities) makes this form logically valid. The slippery slope argument remains a fallacy if such a chain is not established.
Examples
Eugene VolokhEugene Volokh
Eugene Volokh is an American legal commentator and the Gary T. Schwartz Professor of Law at the UCLA School of Law...
'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. Gun-control opponents argue against limits on the sale of "assault weapons" because the confiscation of sportsmen's shotguns will soon follow. Meanwhile, government officials defend their inflexible enforcement of a regulation, even in circumstances that some see as unfair, because allowing an exception would open the floodgates.
- Legal rule combination: Previously the government might need to search every house to confiscate guns, and such a search would violate the Fourth Amendment to the United States ConstitutionFourth Amendment to the United States ConstitutionThe Fourth Amendment to the United States Constitution is the part of the Bill of Rights which guards against unreasonable searches and seizures, along with requiring any warrant to be judicially sanctioned and supported by probable cause...
. 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, colloquially referred to as the "boiling frogBoiling frogThe boiling frog story is a widespread anecdote describing a frog slowly being boiled alive. The premise is that if a frog is placed in boiling water, it will jump out, but if it is placed in cold water that is slowly heated, it will not perceive the danger and will be cooked to death...
": 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 ceilingPrice ceilingA price ceiling is a government-imposed limit on the price charged for a product. Governments intend price ceilings to protect consumers from conditions that could make necessary commodities unattainable. However, a price ceiling can cause problems if imposed for a long period without controlled...
s 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.
Sometimes a single action does indeed induce similar latter action. For example, judiciary decisions may set legal precedents.
As a fallacy
The heart of the slippery slope fallacy lies in abusing the intuitively appreciable transitivity of implication, claiming that A leads 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 slope fallacies occur when this is not done—an argument that supports the relevant premises is not fallacious and thus isn't a slippery slope fallacy.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
Genetic fallacy
The genetic fallacy is a fallacy of irrelevance where a conclusion is suggested based solely on something or someone's origin rather than its current meaning or context. This overlooks any difference to be found in the present situation, typically transferring the positive or negative esteem from...
, 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 amount of trees would fall; however 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 fewer 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
Domino effect
The domino effect is a chain reaction that occurs when a small change causes a similar change nearby, which then will cause another similar change, and so on in linear sequence. The term is best known as a mechanical effect, and is used as an analogy to a falling row of dominoes...
" approaches zero probability.
This form of argument often provides evaluative judgments on social change
Social change
Social change refers to an alteration in the social order of a society. It may refer to the notion of social progress or sociocultural evolution, the philosophical idea that society moves forward by dialectical or evolutionary means. It may refer to a paradigmatic change in the socio-economic...
: 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
Validity
In logic, argument is valid if and only if its conclusion is entailed by its premises, a formula is valid if and only if it is true under every interpretation, and an argument form is valid if and only if every argument of that logical form is valid....
, 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
Conjunction fallacy
The conjunction fallacy is a logical fallacy that occurs when it is assumed that specific conditions are more probable than a single general one.The most often-cited example of this fallacy originated with Amos Tversky and Daniel Kahneman:...
: with a long string of steps leading to an undesirable conclusion, the chance of all the steps actually occurring in sequence is 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
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 soundnessSoundness
In mathematical logic, a logical system has the soundness property if and only if its inference rules prove only formulas that are valid with respect to its semantics. In most cases, this comes down to its rules having the property of preserving truth, but this is not the case in general. The word...
on the validity of some analogue for the physical principle of momentum
Momentum
In classical mechanics, linear momentum or translational momentum is the product of the mass and velocity of an object...
. This may take the form of a domino theory
Domino theory
The domino theory was a reason for war during the 1950s to 1980s, promoted at times by the government of the United States, that speculated that if one state in a region came under the influence of communism, then the surrounding countries would follow in a domino effect...
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
Physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
, 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
Status quo
Statu quo, a commonly used form of the original Latin "statu quo" – literally "the state in which" – is a Latin term meaning the current or existing state of affairs. To maintain the status quo is to keep the things the way they presently are...
, 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
Another analogy resembles mathematical inductionMathematical induction
Mathematical induction is a method of mathematical proof typically used to establish that a given statement is true of all natural numbers...
. Consider the context of evaluating each one of a class of events A1, A2, A3,..., An (for example, is the occurrence of the event harmful or not?). We assume that for each k, the event Ak is similar to Ak+1, so that Ak has the same evaluation as Ak+1.
Therefore every An has the same evaluation as A1.
For example, the following arguments fit the slippery slope scheme with the inductive interpretation
- If we grant a building permit to build a religious structure in our community, then there will be no bound on the number of building permits we will have to grant for religious structures and the nature of this city will change. This argument instantiates the slippery slope scheme as follows: Ak 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 religious structures 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 each building permit will not be evaluated the same way (for example, the more religious structures in a community, the less likely a permit will be granted for another).
See also
- Argument from setting a precedentArgument from setting a precedentArgument from precedent is a common fallacy in discussion, for example on committees or in meetings. It consists in saying that to act correctly in circumstances X would be inadvisable, in case others consider that this would set a precedent for acting in circumstances Y, where X and Y are...
- Creeping normalcyCreeping normalcyCreeping normalcy refers to the way a major change can be accepted as the normal situation if it happens slowly, in unnoticed increments, when it would be regarded as objectionable if it took place in a single step or short period...
- First they came...First they came..."First they came…" is a famous statement attributed to pastor Martin Niemöller about the inactivity of German intellectuals following the Nazi rise to power and the purging of their chosen targets, group after group...
- Gateway drug theory
- Hair-splitting
- Foot-in-the-door techniqueFoot-in-the-door techniqueFoot-in-the-door technique is a compliance tactic that involves getting a person to agree to a large request by first setting them up by having that person agree to a modest request. The foot-in-the-door technique succeeds due to a basic human reality that social scientists call “successive...
- Legal precedent
- Overton windowOverton windowThe Overton window, in political theory, describes a "window" in the range of public reactions to ideas in public discourse, in a spectrum of all possible options on a particular issue. It is named after its originator, Joseph P...
- Parade of horriblesParade of horribles-As a literal parade:"Parade of horribles" originally referred to a literal parade of people wearing comic and grotesque costumes, rather like the Philadelphia Mummers Parade...
- Sorites paradoxSorites paradoxThe sorites paradox is a paradox that arises from vague predicates. The paradox of the heap is an example of this paradox which arises when one considers a heap of sand, from which grains are individually removed...