medium · LSAT Logical Reasoning

No one who is tired can concentrate. Peter is not tired. Therefore, Peter can concentrate.

Which of the following correctly evaluates this reasoning?

  1. Invalid, because it affirms the consequent rather than reasoning forward from the stated trigger.
  2. Valid by modus ponens, since the stated trigger is met and its proper consequence then follows.
  3. Invalid, because it negates the triggering condition and infers the absence of the stated barrier.
  4. Valid by modus tollens, since denying the consequent here properly yields the negated antecedent.
  5. Invalid, since no claim at all about a person's tiredness can ever bear on their concentration here.

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