Biconditional
LSAT glossary · Logical Reasoning
Definition
A two-way conditional in which each term is both sufficient and necessary for the other: P ↔ Q means both P → Q and Q → P. In natural language it appears as "P if and only if Q" or "either both P and Q, or neither." On the LSAT, biconditionals are powerful because triggering either side forces the other, and negating either side forces the negation of the other.
Biconditional in plain English
A biconditional is a two-way street between two things: if you have one, you MUST have the other, and it works in both directions. The phrase to watch for is "if and only if" — so "you pass the class if and only if you get a 60" means getting a 60 guarantees passing, AND passing guarantees you got a 60; there's no way to have one without the other. Think of it like a light switch wired to a single bulb: flip the switch on, the bulb is on; see the bulb on, you know the switch is on. That tight two-way link is what makes biconditionals so useful — knowing either side instantly tells you everything about the other.
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