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Difficulty: MediumTime Shift Flaws (Past vs. Future)

City Council Member: Over the past fifteen years, our city's transition to using a new synthetic asphalt binder has directly caused a steady decrease in our annual road maintenance costs. Since we plan to continue using this synthetic binder exclusively, we can confidently project that our annual road maintenance costs will continue to decrease over the next ten years.

Which one of the following most accurately describes a flaw in the city council member's reasoning?

  1. takes for granted that a trend observed in the past will necessarily persist into the futureAnswer
  2. B
    confuses a mere correlation between the use of the synthetic binder and decreased maintenance costs with a causal relationship
  3. C
    infers a claim about all future years from evidence that supports only a claim about some past years
  4. D
    fails to distinguish between a subsidiary conclusion regarding the past success of the transition and the main conclusion regarding future costs
  5. E
    relies on an ambiguous shift in the meaning of the term 'maintenance' between the premises and the conclusion

Answer

The correct answer identifies that the argument illicitly assumes a historical trend will continue indefinitely into the future.
The argument commits a classic Time Shift Flaw. It takes a historical trend (a steady decrease in maintenance costs over 15 years) and improperly projects it into the future. It fails to consider that the initial savings might have represented a one-time optimization curve, and that costs cannot decrease indefinitely (eventually hitting a floor).

Step-by-Step Solution

1
Analyze the argument's structure.
Premise: Using the new binder caused costs to decrease steadily over the past 15 years. Conclusion: Costs will continue to decrease over the next 10 years because the binder will still be used.
Deconstructing the argument is the first step to evaluating its logical validity.
2
Identify the gap between the premise and the conclusion.
The argument uses historical data (past 15 years) to make a definitive projection about the future (next 10 years) without guaranteeing conditions will remain the same.
Finding the unwarranted assumption reveals the logical flaw.
3
Determine the specific logical fallacy committed.
The author assumes that a past trend of cost reduction will continue indefinitely. It is entirely possible that the maximum cost-saving benefit of the new binder has already been reached, and costs will now stabilize.
Naming the specific flaw (Time Shift Flaw) makes it easier to match with the correct abstract answer choice.
4
Evaluate the options against the identified flaw.
The correct option perfectly describes the assumption that a past trend will persist into the future.
This confirms the answer without falling for trap choices that describe different fallacies.

Key Concept

Time Shift Flaws occur when an argument improperly projects past or present conditions, trends, or behaviors into the future without establishing that the underlying circumstances will remain unchanged.
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Topics

Time Shift Flaws (Past vs. Future)

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