Analytical and Logical Reasoning
Validity is not truth
Logical reasoning items reward treating the stated premises as the whole world, even when they conflict with what you know. Judge whether a conclusion follows, not whether it is factually accurate.
Key concepts: deductive validity; conditional reasoning; necessary versus sufficient conditions; quantifiers (all, some, none); syllogisms; assumptions versus inferences; strengthening and weakening arguments; sampling and correlation versus causation.
For a conditional "If P, then Q," only two inferences are valid: P therefore Q (modus ponens), and not-Q therefore not-P (contrapositive). The converse (Q therefore P) and the inverse (not-P therefore not-Q) are invalid. "All agents are trained" does not license "all trained people are agents."
Traps: the converse error dressed in realistic language; "some" read as "most"; conclusions merely consistent with the premises rather than required by them; answers that import outside facts; confusing a needed assumption with a restatement of the conclusion.
Rule of thumb: for inference questions ask, "Could the premises be true and this answer false?" If yes, it is not a valid inference. For assumption questions, negate the choice - if the argument collapses, the assumption was necessary.
Worked example: "If the badge is expired, entry is denied. Entry was not denied." By contrapositive, the badge was not expired. Concluding "the badge is valid" adds a claim about validity that the premises never supplied.