I asked him about this quote from J. Z. Smith; he replied that he was correct, religion is a constructed category, but that didn’t mean it wasn't also real. So Latour takes the constructionist agenda of the post-structuralists a step further. Our categories are indeed invented, but not “merely” so, for they are also real. They become real through our wielding of them.
The story goes that somewhere on the West Coast of Africa, sometime in the 17th Century,