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The Legitimacy and Fallaciousness of the Slippery Slope

Estimated Lesson Time: 30 minutes (self-evaluated option) / 1 hour (instructor-evaluated option)

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Lesson Introduction

In this lesson, we focus on the Slippery Slope argument or fallacy, also known as: absurd extrapolation, thin edge of the wedge, camel's nose, and domino fallacy.

When a relatively insignificant first event is suggested to lead to a more significant event, which in turn leads to a more significant event, and so on, until some ultimate, significant event is reached, where the connection of each event is not only unwarranted, but with each step it becomes more and more improbable. Many events are usually present in this fallacy, but only two are actually required—usually connected by “the next thing you know...”

We will look when this is a legitimate argument, and when it is fallacious. More important, we will explore why.

Lesson Resources

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Lesson Videos

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Introduction to Lesson 14 (00:54)

Slippery Slope (02:26)

When a relatively insignificant first event is suggested to lead to a more significant event, which in turn leads to a more significant event, and so on, until some ultimate, significant event is reached, where the connection of each event is not only unwarranted, but with each step it becomes more and more improbable. Many events are usually present in this fallacy, but only two are actually required -- usually connected by “the next thing you know...”

Basically Science (02:02)

Science that attempts to establish causality is basically a legitimate slippery slope.​

Evidence (02:14)

Evidence is one of the factors that needs to be considered when deciding if a slippery slope is fallacious or not.

Number of Events (02:40)

​The number of events in the causal chain is one of the factors that needs to be considered when deciding if a slippery slope is fallacious or not.​

Confidence vs. Probability (03:41)

​The confidence level and probability of each event in the causal chain is one of the factors that needs to be considered when deciding if a slippery slope is fallacious or not.​

Lesson Key Points

Slippery Slope Fallacy: When a relatively insignificant first event is suggested to lead to a more significant event, which in turn leads to a more significant event, and so on, until some ultimate, significant event is reached, where the connection of each event is not only unwarranted, but with each step it becomes more and more improbable.
Legitimate Slippery Slope: When a first event is theoretically or empirically demonstrated to be causally linked to a more significant event, in which that event is theoretically or empirically demonstrated to be causally linked to a more significant event.
Scientific studies that demonstrate or suggest causality can be viewed as a form of the slippery slope, where A leads to B.
The less theoretical or empirical evidence between events, the more fallacious the argument.
The greater the number of events in the slope, the more fallacious the argument is likely to be due to multiplication of probabilities.
The greater the disparity in confidence expressed versus the statistical probability of the final event, the more fallacious the argument.

Lesson Assignments

Assignment #1:

This assignment is for students with the instructor-evaluated course option.

Make two arguments using the slippery slope: one fallacious and one legitimate. Then, explain why the one is fallacious and the other is not. 1-2 paragraphs.
Assignment #2Take a minute to answer at least one of the following questions in the discussion section below:

What was the most important thing you learned in this lesson?

What question do you have about this lesson?

How would you sum up this lesson in one sentence?


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Lesson Quiz

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Lesson Progress Course Progress Here you will see a visual and numeric representation of your course progress. Lessons

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#3: Appeal to Common Belief
#4: Fallacies and Religion
#5: Deception Through Confusion
#10: Fallacies of Poor Statistical Thinking
#11: Black and White Thinking
#12: The Impossible and the Possible
#13: The Red Herring
#15: Special Pleading
#16: The Analogy - Both Friend and Foe
#17: A Look at Nature
#18: Fallacies Worthy of Mention

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Lesson Quiz

Be sure to click the "Submit Quiz Answers" at the end of the quiz to save and submit your quiz answers. Select the best answer.

1) The slippery slope is always fallacious
a) true
b) false
2) Which is the most important in establishing legitimacy of a slippery slope?
a) timing
b) the person
c) evidence
d) contract law
3) The less theoretical or empirical evidence between events
a) the more fallacious the argument
b) the less fallacious the argument
4) The fewer events in the slope
a) the more fallacious the argument
b) the less fallacious the argument
5) The greater the disparity in confidence expressed versus the statistical probability of the final event
a) the more fallacious the argument
b) the less fallacious the argument
submitting answers...

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