Comments

• 1 Like

  LSAT Lizard Alum Member

  July 2021 edited July 2021 331 karma

  It is always true that the thing before the arrow is sufficient for the thing after, and the thing after is necessary for the thing before.

  A --> B
  A is sufficient to ensure B.
  B is necessary in order to have A.

  You could also have two rules:
  A --> B
  B --> A
  A is sufficient to ensure B.
  B is sufficient to ensure A.
  B is necessary in order to have A.
  A is necessary in order to have B.

  So don't think that just because something is sufficient, it must not be necessary, or that because something is necessary, it must not be sufficient. It's also possible for something to be sufficient AND necessary when two different conditionals combine like that.

  You could also write both those rules with a double arrow:
  A <--> B

  So whenever you see a double arrow you can think "A is sufficient and necessary for B, and B is sufficient and necessary for A." This combination would usually be spoken as "A if and only if B."