It is argued that improving psychology's internal consistency is a scientific necessity. One precondition is that proponents of various 'scientific" and "humanist" approaches come to agreement on mission and methodological standards of psychology as a scientia (= wetenschap - science). The resulting demarcation problem is solved, in principle, by (Forum) theoretical definitions of the 'scientific truth" and 'scientific import" of statements. On this basis, (signific) concept analysis can provide agreeable definitions of basic concepts, to be proposed for (modification and) actual agreement in consensus groups. It is concluded that these laborious 'scientia"-activities are badly needed and instrumental in serving the goal of unifying psychology.