The idea in the system is that everyone has a dominant style, but there's always a secondary style. Possible combinations are D/I, D/C, I/D, I/S, S/C, S/I, C/S, and C/D. D and S are opposites that are not found together (unless one's environment forced him/her to adapt and take on traits of their opposite), as are I and C.
Therefore, if someone isn't sure what type they are because a few of their scores are close, they can look at their lowest score to help them determine it. Implied, for example, would be either an S/I or an S/C (according to her test scores).