No you do not. Read the PHB section on grappling. Normal PCs and monsters take a -4 penalty if they want to deal "normal" damage, otherwise it is subudal. Monks may deal either normal or subdual damage w/o penalty.
The way I read that section seemed to indicate that only in a grapple could monks choose to switch back and forth between the two, the rest of the time they take the normal -4 to hit.
The way I read that section seemed to indicate that only in a grapple could monks choose to switch back and forth between the two, the rest of the time they take the normal -4 to hit.