An LSAT conditional indicator that introduces a necessary condition, equivalent to "if not." "A unless B" translates to ¬B → A (and equivalently ¬A → B): without B, A must occur — B is the necessary condition that prevents A. Example: "You can't drive unless you are at least sixteen" translates to drive → at least 16. The "Unless" Mantra is to negate the "unless" clause and place the remainder on the sufficient side.