Roscellinus of Amorica in Brittany (1050-1121) was the founder of nominalism, another approach to universals. A universal, he said, is just a “flatus vocis” (a vocal sound -- i.e. a word). Only individuals actually exist. Words, and the ideas they represent, refer to nothing. This is quite compatible with materialism and empiricism, but not, really, to Christianity.

It, too, is not without problems: If words are nothing but air, then reason (and philosophy), which is the manipulation of these words, is nothing but blowing air (as many students in fact believe). That includes, of course, the reasoning it took to come to the nominalist conclusion!

Regarding the church, nominalism means that the church is nothing but the people that compose it, and religion is just what individuals think. And, if God is Father, Son, and Holy Ghost, then we can't be monotheists.