Necessary and Sufficient

A necessary condition is one you cannot do without. A sufficient condition is one that is enough by itself. They are not the same door. Oxygen is necessary for a fire and not sufficient. A lit match in a dry stack can be enough, given the oxygen already there.

Arguments often slide from “needed” to “enough,” or from “enough in this case” to “required in every case.” The slide sounds like logic and is only one word swapped for another.

Write the word you mean. “Only if” is necessary. “If” by itself is often sufficient. Mixing them builds a policy no one voted for.

The requirement

A film festival’s rules say a film must run under two hours to enter. A three-hour film is turned away, fairly. A juror then says, “It ran under two hours, so it must be a great film,” and skips the screening.

Running time was necessary. It was not sufficient. Having the ticket gets you to the door. It does not walk through it.

Try this today Take one rule at work or home and mark which parts are required and which are actually enough.