Confusing sufficiency and necessity

(SuffvNec)

The "oldest mistake in the book." Arguments that confuse a sufficient condition for a necessary condition. For example, the claim A → B is confused for B → A or /A → /B.

Avg. 0.6 per section
3%
21%
36%
30%
10%

Avg. difficulty: 3.2

Key tactics

  • We call this flaw the "oldest mistake in the book" because you are guaranteed see this multiple times in every PrepTest.

Answer choice tips

  • Example answer choices that point to this flaw:
  • assumes without warrant that just because satisfying a given condition is enough to ensure an announcement’s importance, satisfying that condition is necessary for its importance.
  • (In response to a stimulus that presents a premise saying "A -> B" but concludes "B -> A"): ignores the possibility that B may sometimes happen while A does not happen.
  • mistakenly interprets P to be claiming that a factor assures, rather than is necessary for, a legislator’s effectiveness.

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Logical reasoning question types

Argument part Evaluate Fill in the blank Flaw or descriptive weakening Inference Main conclusion or main point Method of reasoning or descriptive Most strongly supported Must be false Must be true Necessary assumption Parallel flawed method of reasoning Parallel method of reasoning Point at issue: agree Point at issue: disagree Principle PSA - find or complete the application PSA - find the rule Resolve reconcile or explain Strengthen Sufficient assumption Weaken

Reading comprehension question types

Analogy (RC) Application Author’s attitude Author’s perspective Describe approach Describe organization Describe relationship Implied Logical continuation Main point Meaning in context (of word, phrase, or idea) Other’s perspective Principle or generalization Purpose in context (of word, phrase, or idea) Purpose of paragraph Purpose of passage Stated Structure WSE (RC)

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