An LSAT conditional indicator that introduces a necessary condition: "A only if B" translates to A → B (B is necessary for A). This is the single most commonly confused conditional translation — many test-takers misread "only if" as "if," reversing the arrow. Example: "You can enter the club only if you have a membership card" means enter → card; having a card is necessary, but does NOT guarantee entry. The rule: "only" introduces the necessary condition, never the sufficient.