The question of the legitimacy of the secularization thesis (no not that secularization thesis, the other one)hinges in part on the interpretation of spiritual ownership, a concept which has been much discussed in the short life of this blog. What Blumenberg calls the "background metaphor" of the idea that progress (and a raft of related modern tropes) are not legimitate productions of modernity but taken and twisted from Christian theology is the notion of ideas as spiritual property. How one takes "property" here will determine in what respects it makes sense to speak of modernity acquiring the property of its historical predecessor.
The "anachronism" of the secularization thesis , according to Blumenberg, lies in the difference between the criteria of legitimate ownership respectively maintained by the Christian and modern epochs. From the perspective of Christian theology, "legitimate ownership arises through acquisition from the hand that has disposition over the object." The modern epoch, on the other hand, "produced the axiom that the legitimate ownership of ideas can be derived only from their authentic production." These concepts of ownership as applied to spiritual ownership determine the possibilities of tradition.