2nd–3rd centuries
Sabellianism / Modalism
Father, Son, and Holy Spirit are not three distinct persons, but modes, roles, or manifestations of one God.
The Central Error
It protects divine oneness by denying the real personal distinction of Father, Son, and Holy Spirit.
Historic Response
Sabellius was condemned and excommunicated in Rome; the teaching was rejected by the broader orthodox Trinitarian tradition.
Modern Echoes
Oneness Pentecostal or “Jesus Only” theology is commonly classified as modalistic by Nicene Christians, though adherents may reject the label Sabellian.