What is "subordinationism"

Subordinationism is a heresy in Christianity that asserts that God the Son and God the Holy Spirit are subordinate to God the Father in nature and being. Various forms of subordinationism were believed by some in early Christianity until the mid 4th century, when the Arian controversy was settled, after many decades of formulating of the doctrine of Trinity, by the First Council of Constantinople in 381 which condemned Arianism.

Subordinationism has common characteristics with Arianism. the Arians went even further to assert that the Son was a created being, and was therefore not eternal, and therefore he is inferior in nature to the Father, whom they believed to be the One and Only God. Subordinationism in its various forms thrived at the same time as Arianism, but long survived it. Its chief proponents in the 4th century were Arius of Alexandria, after whom the view is most commonly named, and Eusebius of Nicomedia. Athanasius of Alexandria and his mentor and predecessor, Alexander of Alexandria, battled Arian subordinationism as patriarchs of Alexandria.

In most orthodox Christian theological circles, Arian subordinationism is treated as heresy, In other circles, subordinationism is seen as biblical middle ground between extremes of Modalism and Unitarianism. ( Christology has been the source of many (but not all) hot disputes and subsequent divisions of Christianity since the 1st century AD)