The referee may use a character’s ability scores to determine the character’s chance of succeeding at various challenging tasks.

The player rolls 1d20 and, if the result is less than or equal to the ability, the check succeeds. If the roll is greater than the ability, the check fails.

Bonuses or penalties to the roll may be applied, depending on the difficulty of the task. A modifier of -4 would be a relatively easy ability check, and a +4 would be very difficult.

A natural 1 should be treated as a success and a natural 20 treated as a failure.