Because Tertullian thus had the unfolding of the divine threeness already happening with a view to creation and redemption, the step to the doctrine of the Trinity was easily taken. The controversy with Monarchianism and Patripassianism carried on in the Praxeas gives us Tertullian's characteristic christological ideas and terminology. The tri-personality of one God is an unconditional presupposition for his understanding of the mystery of the incarnation. As regards Tertullian's contribution, it is really only certain elements in his vocabulary along with his clear perception of what main errors had to be avoided that became crucial and of final importance for christology - in vocabulary particularly, his use of substantia and persona.