[@BS], stressing applications to CP violation. Refs. [@BS; @BLS] indicate how to construct basis invariant quantities in a systematic fashion for any model, including multi-Higgs-doublet models. A number of recent articles concerning symmetries and/or basis invariance in the THDM include Refs. [@Gun; @BRSM; @GK; @DavHab; @Haber; @oneil; @Nishi; @NachMani; @Ivanov1; @Ivanov2; @Gerard; @FS2; @FHS].

It is remarkable that there are exactly six classes of symmetries that one may impose on the scalar sector of the most general THDM. This was shown by Ivanov [@Ivanov1] and expanded upon by us in Ref. [@FHS]. Since the Higgs sector of the MSSM is a particular case of the THDM, one would expect that the constraints satisfied by the Higgs sector of the MSSM would correspond to one of the six classes of symmetries identified in the scalar sector of the THDM. This is *not* the case. The correct conclusion is that a physically meaningful definition of the supersymmetric limit must involve the interaction of the Higgs sector with other sectors of the supersymmetric theory. In this article we construct basis-invariant probes of supersymmetry involving both the Higgs sector and the gaugino-higgsino-Higgs interactions.

This article is organized as follows. In section \[sec:notation\] we introduce 