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Difficulty: HardFlaw in the Reasoning

Each excerpt in the first column exhibits a characteristic vulnerability in its logical reasoning. Match each flawed argumentative excerpt with the description that most accurately identifies its primary reasoning flaw:

  • Hydrologist: To prevent saline intrusion into coastal freshwater wells, a municipal aquifer replenishment facility's injection pressure must continuously exceed hydrostatic barrier thresholds. Sensor logs confirm that the Seaside Basin facility maintained injection pressures exceeding these thresholds throughout the dry season. Therefore, the Seaside Basin facility must have successfully prevented saline intrusion during this period.Treats a condition that is strictly necessary for achieving a specific outcome as though it were sufficient to guarantee that outcome.
  • Linguist: Public statutes mandate that governmental notices be drafted in 'plain language' to avoid communicative ambiguity. Because plain language is unadorned and elementary, any notification incorporating specialized technical nomenclature violates this statutory mandate, even if every technical term is defined with complete and unambiguous precision.Relies upon an equivocal shift in the meaning of a key term from an absence of ambiguity to an absence of specialized vocabulary.
  • Ecologist: Every individual invertebrate species inhabiting the Mariana Arc hydrothermal vents exhibits high tolerance to extreme temperature fluctuations. Because the Mariana Arc hydrothermal vent ecosystem consists entirely of these invertebrate populations and their physical habitat, the ecosystem as a whole must be similarly resilient against regional temperature changes.Infers that a collective system possesses a particular characteristic solely from the premise that each individual component part of that system possesses that characteristic.

Answer

The hydrologist's argument matches the description of treating a necessary condition as sufficient; the linguist's argument matches the description of an equivocal shift in the meaning of a key term; and the ecologist's argument matches the description of improperly inferring that a collective system has a trait because its individual parts do.
Each argument corresponds to a classic structural flaw on the LSAT: the hydrologist confuses a necessary condition with a sufficient condition; the linguist shifts the meaning of 'plain language' from unambiguous communication to non-technical diction; and the ecologist commits a fallacy of composition by attributing an individual component trait to an entire systemic whole.

Step-by-Step Solution

1
Analyze the structural relationship between premise and conclusion in the hydrologist's argument.
The hydrologist states that exceeding the pressure threshold is required ('must continuously exceed') to prevent intrusion. Exceeding the threshold satisfies a necessary condition, but the conclusion treats it as sufficient to guarantee the prevention of intrusion.
Identify conditional logic errors (mistaking necessary conditions for sufficient conditions).
2
Evaluate the usage of central terminology across the premises and conclusion in the linguist's argument.
The term 'plain language' is initially introduced in the context of preventing ambiguity, but is subsequently redefined as the absence of any technical vocabulary, creating an illegitimate semantic shift.
Identify equivocation and definitional shifts that undermine deductive validity.
3
Assess the compositional relationship between the entities in the ecologist's premises and conclusion.
The premise establishes a property of individual species ('each individual invertebrate species'), while the conclusion attributes that same property to the collective entity ('the ecosystem as a whole').
Identify compositional fallacies (part-to-whole / composition errors).

Key Concept

Flaw in the Reasoning: Structural Fallacies and Error Identification
Estimated Time:2m 30s
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Flaw in the Reasoning

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