Fraenger' s assertion that the artist Hieronymus Bosch belonged to the Brethren of the Free Spirit, a nonmainstream religious group, is unlikely to be correct  Fraenger' s hypothesis explains much of Bosch' s unusual subject matter
However, there is evidence that Bosch was a member of a mainstream church, and no evidence that he was a member of the Brethren
It is intended to help show that Bosch's choice of subject matter remains unexplained.