What's the extra knife for?

So I recently ate at this really nice restaurant and there was so much silverware. Three forks on the left, spoon fork spoon above, then knife soup spoon knife to the right. I know what the three forks were for and all the silverware above the plate, but I never could figure out what the OTHER knife was for. It wasn't the er knife, because that was on the roll plate. Was it in case I needed to cut the appetizer? By the way, it was a 4-course meal.