Ethicist: A society is just when, and only when, first, each person has an equal right to basic liberties, and second, inequalities in the distribution of income and wealth are not tolerated unless these inequalities are to everyone’s advantage and are attached to jobs open to everyone.
Principle
The word "when" (like if) is a sufficient indicator, meaning we put that idea on the LEFT side of the arrow, whereas the idea "only when" (like only if) is a necessary indicator, meaning we put that idea on the RIGHT side of the arrow.
If we have "when and only when" then we're getting a bi-conditional, because we're saying that an idea belongs on the left and the right side of the arrow.
But an even simpler way to think about bi-conditionals is that they're just either / ors