Complex space-time and the classification of elementary particles

It is shown that the Dirac theory implies complex space-time and complex space-time can lead to the Dirac equation. It is suggested that fermions are grouped into doublets, those doublets are then divided into color singlets (leptons) and color triplets (quarks), then they are further divided into generation singlets and generation triplets. If the exclusion principle for fermions works in the internal space, then the non-observation of free quarks can be explained. However, it is suggested that a possible new free quark may exist with a color triplet and generation singlet state which is antisymmetric in the internal space.