Circumstance Bonus

Circumstance bonuses arise from specific conditional factors affecting the task at hand. Circumstance bonuses stack with other circumstance bonuses unless they arise from essentially the same source, in which case they do not stack.

For example, you might use a firecracker as part of a Bluff check to create a distraction. The GM decides the firecracker grants a +2 circumstance bonus to the skill check. The GM also knows the guards in this situation are extremely nervous, and thus their attention is easily drawn to any sudden or unexpected occurrence. The GM grants you a +2 circumstance bonus as well. Since these two bonuses result from distinct circumstances that both affect the task, they stack, granting you a +4 bonus to the Bluff check.