All classes in S&W have a single saving throw that may be used as a general ‘task resolution’ mechanism. Under this system, when attempting a particular task, the player rolls 1d20, applies any relevant attribute modifiers (a bonus of +1, a penalty of -1, or no modifier, depending on the attribute score), and any additional modifiers that the GM judges appropriate. Very easy, but not automatically successful, tasks might receive a bonus of +10, while extremely difficult, but not impossible, tasks might receive a penalty of -10. Less extreme modifiers should apply to rolls involving tasks of intermediate ease or difficulty. The difficulty modifier is applied to the character’s saving throw roll. (It is up to the GM to determine whether the player has knowledge of this modifier.) If the modified roll equals or exceeds the character’s saving throw number, the task is successful. An unmodified roll of a 20 always indicates success, and an unmodified roll of a 1 always indicates failure (otherwise, there is no point in making the roll in the first place, and the GM should simply decide that the character automatically succeeds or fails).
For example, Nibold the Purple, a bold roguish warrior, is attempting to swim across a dangerous rushing river. Because Nibold is a fifth level fighter, his base saving throw number is 12. The GM judges that superior strength would assist anyone attempting such a feat, and thus allows the player to apply Nibold’s strength bonus, in this case +1, to the roll. Because the river is flowing swiftly, and contains dangerous rocks and currents, the GM assigns a -2 penalty to the player’s roll. Finally, the GM notes that Nibold’s background is that of a sailor, and therefore grants the character a +4 bonus to the roll. This leaves the player with a net +3 bonus to his roll for Nibold. The player rolls a 10 and adds 3 for a total of 13. Since that exceeds Nibold’s saving throw number of 12, Nibold successfully swims across the river. If the player had failed his roll, the GM may have decided that Nibold suffered 1d6 points of damage from being bashed about the rocks by the stream’s strong currents. A roll of a natural 1 may have resulted in Nibold being knocked unconscious, and likely drowning to death, unless rescued by his compatriots (assuming that he has some nearby!).
Finally, GMs should always exercise discretion when using this system. It should not replace common sense or player creativity. If the task in question is one that any normal human being would typically succeed at accomplishing, then a roll should be unnecessary. Avoid having players roll to determine if their characters can climb a ladder, jump across a three foot crevice, or swim across a calm pond. Moreover, if a player comes up with an ingenious plan to overcome some difficulty or challenge, the GM may want to reward that player by allowing the plan to succeed without a roll, or, if the GM thinks that the plan is risky enough to require a roll, with a positive modifier. Interesting and daring plans make the game more exciting for everyone, and thus generally should be rewarded by GMs. (Foolish plans, on the other hand, are rightfully mocked!)
(Published in Knockspell #2.)
EDIT: In the third printing of S&W, fighters and magic-users both start with a saving throw of '15,' and improve by 1 per level until level 11. Clerics retain their original saving throws.