Abstract
William of Conches and others natural philosophers in the early 12th century frequently discussed the connection between the material body and the immaterial soul of human beings. This especially concerns the platonic tertium genus of Hyle/Silva as well as the Christian concept of subtle bodies. For historical reasons is the theory of the four elements a key-concept in this discussion; one could gradually continue the process of refining matter beyond the subtle element ‘fire’ until there is a zone reached, which is so subtle and refined that it is hard to decide, whether it is still matter or already a slightly materialized part of the immaterial soul. Various texts show a branch of experimental thinking in the 12th century European philosophy which was based on the platonic philosophy and which vanished with the upcoming of the Aristotelian doctrine.