A slippery slope argument (SSA), in logic, critical thinking, political rhetoric, and caselaw, is a consequentialist logical device in which a party asserts that a relatively small first step leads to a chain of related events culminating in some significant (usually negative) effect. The core of the slippery slope argument is that a specific decision under debate is likely to result in unintended consequences. The strength of such an argument depends on the warrant, i.e. whether or not one can demonstrate a process that leads to the significant effect. This type of argument is sometimes used as a form of fear mongering, in which the probable consequences of a given action are exaggerated in an attempt to scare the audience. 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. In a non-fallacious sense, including use as a legal principle, a middle-ground possibility is acknowledged, and reasoning is provided for the likelihood of the predicted outcome. Other idioms for the slippery slope argument are the thin end/edge of the wedge and the camel's nose in the tent.
1 Slopes, arguments and fallacies 2 Types of slippery slope argument 3 The metaphor and its alternatives
3.1 Thin end of a wedge 3.2 Domino fallacy 3.3 Dam burst 3.4 Other metaphors
4 Defining features of slippery slope arguments 5 Non-fallacious usage 6 See also 7 References 8 External links
Slopes, arguments and fallacies Some writers distinguish between a slippery slope event and a slippery slope argument.:122 A slippery slope event can be represented by a series of conditional statements, namely:
if p then q; if q then r; if r then … z.
The idea being that through a series of intermediate steps p will
imply z. Some writers point out that strict necessity isn't required
and it can still be characterized as a slippery slope if at each stage
the next step is plausible.:186 This is important for with
strict implication p will imply z but if at each step the probability
is say 90% then the more steps there are the less likely it becomes
that p will imply z.
A slippery slope argument is typically a negative argument where there
is an attempt to dissuade someone from taking a course of action
because if they do it will lead to some unacceptable conclusion.
Some writers point out that an argument with the same structure might
be used in a positive way in which someone is encouraged to take the
first step because it leads to a desirable conclusion.
If someone is accused of using a slippery slope argument then it is
being suggested they are guilty of fallacious reasoning and whilst
they are claiming that p implies z, for whatever reason, this is not
the case. In logic and critical thinking textbooks slippery slopes and
slippery slope arguments are normally discussed as a form of fallacy
although there may be an acknowledgement that non-fallacious forms of
the argument can also exist.:273–311
Types of slippery slope argument
Different writers have classified slippery slope arguments in
different and often contradictory ways,:273–311 but there are two
basic types of argument that have been described as slippery slope
arguments. One type has been called the causal slippery
slope,:308 and the distinguishing feature of this type is that
the various steps leading from p to z are events with each event being
the cause of the next in the sequence. The second type might be
called the judgmental slippery slope with the idea being that the
'slope' does not consist of a series of events but is such that, for
whatever reason, if a person makes one particular judgment they will
rationally have to make another and so on. The judgmental type may be
further sub-divided into conceptual slippery slopes and decisional
Conceptual slippery slopes, which
Trudy Govier calls the fallacy of
slippery assimilation, are closely related to the sorites
paradox so, for example, in the context of talking about slippery
slopes Merilee Salmon can say, "The slippery slope is an ancient form
of reasoning. According to van Fraassen (The Scientific Image), the
argument is found in
Christopher Tindale gives a definition that only fits the causal type. He says, " Slippery Slope reasoning is a type of negative reasoning from consequences, distinguished by the presence of a causal chain leading from the proposed action to the negative outcome.":185 Merrilee Salmon describes the fallacy as a failure to recognise that meaningful distinctions can be drawn and even casts the "domino theory" in that light. Doug Walton says that an essential feature of slippery slopes is a "loss of control" and this only fits with the decisional type of slippery slope. He says that, "The domino argument has a sequence of events in which each one in the sequence causes the next one to happen in such a manner that once the first event occurs it will lead to the next event, and so forth, until the last event in the sequence finally occurs…(and)…is clearly different from the slippery slope argument, but can be seen as a part of it, and closely related to it."
The metaphor and its alternatives Thin end of a wedge Walton suggests Alfred Sidgwick should be credited as the first writer on informal logic to describe what would today be called a slippery slope argument.:275
"We must not do this or that, it is often said, because if we did we should be logically bound to do something else which is plainly absurd or wrong. If we once begin to take a certain course there is no knowing where we shall be able to stop within any show of consistency; there would be no reason for stopping anywhere in particular, and we should be led on, step by step into action or opinions that we all agree to call undesirable or untrue."
Sidgwick says this is "popularly known as the objection to a thin end of a wedge" but might be classified now as a decisional slippery slope. However, the wedge metaphor also captures the idea that unpleasant end result is a wider application of a principle associated with the initial decision which is often a feature of decisional slippery slopes due to their incremental nature but may be absent from causal slippery slopes. Domino fallacy T. Edward Damer, in his book Attacking Faulty Reasoning, describes what others might call a causal slippery slope but says,
"While this image may be insightful for understanding the character of the fallacy, it represents a misunderstanding of the nature of the causal relations between events. Every causal claim requires a separate argument. Hence, any "slipping" to be found is only in the clumsy thinking of the arguer, who has failed to provide sufficient evidence that one causally explained event can serve as an explanation for another event or for a series of events.":135
Instead Damer prefers to call it the domino fallacy. Howard Kahane
suggests that the domino variation of the fallacy has gone out of
fashion because it was tied the domino theory for the United States
becoming involved in the war in Vietnam and although the U.S. lost
that war "it is primarily communist dominoes that have fallen".:84
Frank Saliger notes that "in the German-speaking world the dramatic
image of the dam burst seems to predominate, in English speaking
circles talk is more of the slippery slope argument":341 and that
"in German writing dam burst and slippery slope arguments are treated
as broadly synonymous. In particular the structural analyses of
slippery slope arguments derived from English writing are largely
transferred directly to the dam burst argument.":343 In exploring
the differences between the two metaphors he comments that in the dam
burst the initial action is clearly in the foreground and there is a
rapid movement towards the resulting events whereas in the slippery
slope metaphor the downward slide has at least equal prominence to the
initial action and it "conveys the impression of a slower
'step-by-step' process where the decision maker as participant slides
inexorably downwards under the weight of its own successive
(erroneous) decisions.":344 Despite these differences Salinger
continues to treat the two metaphors as being synonymous. Walton arges
that although the two are comparable "the metaphor of the dam bursting
carries with it no essential element of a sequence of steps from an
initial action through a gray zone with its accompanying loss of
control eventuated in the ultimate outcome of the ruinous disaster.
For these reasons, it seems best to propose drawing a distinction
between dam burst arguments and slippery slope arguments."
Eric Lode notes that "commentators have used numerous different
metaphors to refer to arguments that have this rough form. For
example, people have called such arguments "wedge" or "thin edge of
the wedge", "camel's nose" or "camel's nose in the tent", "parade of
horrors" or "parade of horribles", "domino", Boiling Frog and "this
could snowball" arguments. All of these metaphors suggest that
allowing one practice or policy could lead us to allow a series of
other practices or policies.":1470
Bruce Waller says it is lawyers
who often call it the "parade of horribles" argument while politicians
seem to favor "the camel's nose is in the tent".:252
Defining features of slippery slope arguments
Given the disagreement over what constitutes a genuine slippery slope
argument it is to be expected that the there are differences in the
way they are defined. Lode says that "although all SSAs share certain
features, they are a family of related arguments rather than a class
of arguments whose members all share the same form.":1476
Various writers have attempted to produce a general
taxonomy of these different kinds of slippery slope. Other writers
have given a general definition that will encompass the diversity of
slippery slope arguments.
The series of intervening and gradual steps The idea that the slope lacks a non-arbitrary stopping place The idea that the practice under consideration is, in itself, unobjectionable
Rizzo and Whitman identify slightly different features. They say, "Although there is no paradigm case of the slippery slope argument, there are characteristic features of all such arguments. The key components of slippery slope arguments are three:
An initial, seemingly acceptable argument and decision; A "danger case"—a later argument and decision that are clearly unacceptable; A "process" or "mechanism" by which accepting the initial argument and making the initial decision raise the likelihood of accepting the later argument and making the later decision."
Walton notes that these three features will be common to all slippery slopes but objects that there needs to be more clarity on the nature of the 'mechanism' and a way of distinguishing between slippery slope arguments and arguments from negative consequences.:275 Corner et al. say that a slippery slope has "four distinct components:
An initial proposal (A). An undesirable outcome (C). The belief that allowing (A) will lead to a re-evaluation of (C) in the future. The rejection of (A) based on this belief.
The alleged danger lurking on the slippery slope is the fear that a
presently unacceptable proposal (C) will (by any number of
psychological processes—see, e.g., Volokh 2003) in the future be
re-evaluated as acceptable."
Walton adds the requirement that there must be a loss of control. He
says, there are four basic components, "One is a first step, an action
or policy being considered. A second is a sequence in which this
action leads to other actions. A third is a so-called gray zone or
area of indeterminacy along the sequence where the agent loses
control. The fourth is the catastrophic outcome at the very end of the
sequence. The idea is that as soon as the agent in question takes the
first step he will be impelled forward through the sequence, losing
control so that in the end he will reach the catastrophic outcome. Not
all of these components are typically made explicit..."
Boiling frog Broken windows theory Butterfly effect Creeping normality Euthanasia and the slippery slope First they came ... Foot-in-the-door technique Gateway drug theory Overton window Precautionary principle Precedent Snowball effect Splitting (psychology) Trivial objections
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^ "Learning to reason clearly by understanding logical fallacies".
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February 20, 2012. Retrieved February 20, 2012.
^ a b c d Rizzo, Mario; Whitman, Douglas (2003). "The camel's nose is
in the tent: rules, theories, and slippery slopes". UCLA Law Review.
51 (2): 539–592. Retrieved 2017-03-18.
^ a b Kelley, David (2014). The art of reasoning: an introduction to
logic and critical thinking (4th ed.). New York London: W.W. Norton
& Company, Inc. ISBN 978-0-393-93078-8.
^ a b Tindale, Christopher (2007). Fallacies and argument appraisal.
Cambridge New York: Cambridge University Press.
^ Groarke, Leo (1997). Good reasoning matters!: a constructive
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^ a b c d Walton, Douglas (2015). "The basic slippery slope argument".
Informal Logic. 35 (3). SSRN 2655360 .
^ a b "Logical fallacy: slippery slope". fallacyfiles.org. Retrieved
^ a b Kahane, Howard (2001).
Propaganda Critic: Unwarranted extrapolation Nizkor: Slippery slope
v t e
Equivocation False equivalence False attribution Quoting out of context Loki's Wager No true Scotsman Reification
False dilemma (Perfect solution fallacy) Denying the correlative Suppressed correlative
Fallacies of illicit transference
Accident Converse accident
Accent Amphibology Continuum fallacy / Sorites paradox False precision Moving the goalposts Slippery slope
Animistic (Furtive) Correlation proves causation (Cum hoc ergo propter hoc) Gambler's (inverse) Post hoc Regression Single cause Slippery slope Texas sharpshooter Third-cause Wrong direction
List of fallacies Other types of fallacy