Slippery Slope and Appeal to Consequences

Some fallacies trade on predictions about the future — claiming that a particular action will inevitably lead to dire outcomes, or that a claim must be true or false because of its consequences. The slippery slope fallacy asserts an unfounded chain of events, whilst the appeal to consequences judges the truth of a claim by its real or imagined outcomes. Both are common in LNAT passages, particularly those discussing policy, law, and ethics.

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The Slippery Slope Fallacy

A slippery slope argument claims that one action will inevitably trigger a chain of events leading to an extreme and usually negative outcome, without providing adequate evidence for each step in the chain.

Structure

Step	What happens
1. Action A is proposed	A specific, often moderate, change
2. A chain of consequences is asserted	"If A, then B; if B, then C; if C, then D..."
3. The final consequence is extreme	D is presented as catastrophic or unacceptable
4. The conclusion	"Therefore we must not do A"
The flaw	No evidence is provided that each step necessarily follows from the previous one

Example

"If we legalise assisted dying for the terminally ill, it will not be long before we extend it to the chronically ill, then to the elderly who feel they are a burden, then to anyone who is depressed. We will end up with a society where the vulnerable are pressured into ending their lives. We must therefore oppose any form of assisted dying."

Each step in this chain — from terminally ill to chronically ill to elderly to anyone depressed — is presented as inevitable, but no evidence is given that any of these transitions would actually occur. Many countries that have legalised limited forms of assisted dying have not experienced this progression.

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When Is a Slippery Slope Fallacious?

Not every prediction of a chain of events is fallacious. The key question is whether adequate evidence is provided for each link in the chain.

Scenario	Fallacious?	Why or why not
"If we raise interest rates by 0.25%, it could dampen consumer spending, which could slow growth" — supported by economic data	Not fallacious	Each step is supported by established economic relationships
"If we allow same-sex marriage, next people will want to marry their pets"	Fallacious	No logical or evidential connection between the two steps
"If we introduce voter ID requirements, some eligible voters who lack ID will be unable to vote, reducing turnout among vulnerable groups" — supported by studies	Not fallacious	Each step is supported by empirical evidence
"If we ban plastic straws, they will ban all plastics, then all packaging, then all manufactured goods"	Fallacious	Absurd escalation with no evidential basis

Key Test: For each step in the chain, ask: "Is there evidence that this step would actually follow from the previous one?" If any link in the chain is unsupported, the argument is a slippery slope.

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Slippery Slopes in LNAT Passages

LNAT passages drawn from opinion writing frequently use slippery slope arguments because they are rhetorically powerful — they generate fear about extreme outcomes and discourage moderate reforms. Look for:

• Chains of increasingly extreme consequences without evidence for each step
• Language of inevitability — "it will not be long before", "this will inevitably lead to", "the logical conclusion is"
• Catastrophic endpoints — the chain always ends somewhere terrible
• No acknowledgement of safeguards — the argument ignores the possibility of limiting measures

Worked Example

"The government's proposal to require social media companies to verify users' ages will be the beginning of the end for online privacy. Once age verification is established, the government will inevitably demand identity verification for all online activity. From there, it is a short step to monitoring what citizens read, say, and think online. History teaches us that surveillance powers, once granted, are never relinquished. This proposal must be defeated to protect our fundamental freedoms."

Question: The argument is most vulnerable to which of the following criticisms?

A. It fails to acknowledge that children should be protected from harmful content. B. It provides no evidence that age verification would necessarily lead to broader identity verification or surveillance, presenting an unsupported chain of increasingly extreme consequences. C. It does not consider the technical feasibility of age verification. D. It assumes that the government has malicious intentions.

Answer: B. The argument leaps from age verification to identity verification to surveillance to thought monitoring without providing evidence that any of these steps would follow from the previous one. The phrase "it is a short step" does the work of logical connection without actually providing it.

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The Appeal to Consequences Fallacy

An appeal to consequences (argumentum ad consequentiam) judges the truth or falsity of a claim based on the desirability or undesirability of its consequences, rather than on evidence.

Two Forms