The Slippery Slope Flaw on the LSAT: When a Chain of Events Doesn't Hold

A slippery slope argument claims that one action or policy will inevitably trigger a chain of events, ultimately leading to some extreme or undesirable outcome. The conclusion is that the first step should be avoided — or that it is dangerous — because of where the chain allegedly leads.

The flaw is not in the chain itself. A chain of consequences can be valid if each link is supported. The flaw is in assuming each step follows necessarily from the previous one without providing evidence that the chain is actually likely to proceed as described.

Put simply: the argument presents a sequence of increasingly serious consequences as if they were inevitable, when in fact each link in the chain needs its own justification.

Slippery slope stimuli have a characteristic shape. The first sentence introduces a modest policy, action, or change. The middle describes a sequence of downstream effects, each building on the previous one. The conclusion warns that the modest first step will lead to something dramatic, harmful, or absurd.

Key language: 'if we allow X, then Y will follow, which will lead to Z, and eventually result in W.' The more steps in the chain, and the more extreme the final outcome relative to the first step, the more likely this is a slippery slope.

Example: 'If the city lowers the speed limit on residential streets by 5 mph, drivers will come to expect ever-lower limits. Over time, the city will keep reducing limits until cars are effectively banned from residential areas, devastating local commerce.'

The flaw: nothing in the argument justifies why a modest speed reduction leads to a total car ban. The chain of steps is asserted, not argued.

Every slippery slope argument is also a causal argument, but not every causal argument is a slippery slope. The correlation-causation flaw involves wrongly inferring that because two things are associated, one must have caused the other. The slippery slope flaw specifically involves an unwarranted chain of future steps, each assumed to follow from the last.

On the LSAT, these are treated as distinct flaw types and described differently in answer choices. A causation flaw answer will mention 'correlation does not establish causation' or 'other factors may explain the relationship.' A slippery slope answer will mention 'assuming one step inevitably leads to further steps' or 'fails to show that the initial action would in fact trigger the chain of events described.'

Do not confuse them when choosing answers. The stimulus type — present observation versus future prediction chain — usually makes the distinction clear.

Flaw questions: The correct answer names the reasoning error, typically phrased as 'assumes without justification that permitting the first step will lead to the described consequences' or 'fails to explain why each step in the series would follow from the preceding one.'

Weaken questions: The best weakener shows that the chain would likely stop somewhere before the extreme conclusion — for example, evidence that other cities lowered speed limits without further reductions, or that a counteracting force would halt the sequence.

Strengthen questions: An argument with a slippery slope structure is strengthened by evidence that the chain has indeed played out in comparable situations, or that no stopping mechanism exists.

Necessary assumption: The argument assumes that nothing will interrupt the chain at any point. An assumption answer might read: 'No policy, social force, or incentive would prevent each subsequent step from following the previous one.'

Example 1: 'If the university allows students to take one final exam remotely, students will demand to take all exams remotely. Professors will then stop writing exams and switch entirely to take-home papers. Academic standards will deteriorate as assignments become easier to complete with outside help. The university should not allow any remote final exams.'

Flaw: the argument assumes each step follows necessarily from the previous one. There is no evidence that allowing one remote exam produces demands for all remote exams, or that paper assignments are inherently less rigorous.

Example 2: 'Once a government taxes soda, it will tax all unhealthy foods. From there it will regulate restaurant menus. Eventually, the government will control every food choice citizens make. We must oppose the soda tax.'

Flaw: the argument provides no mechanism or evidence showing why a soda tax leads to total food control. Each link requires independent justification that the stimulus does not supply.