Modalism (i.e. Sabellianism, Noetianism and Patripassianism)
...taught that the three persons of the Trinity as different “modes” of the Godhead. Adherants believed that Father, Son and Holy Spirit are not distinct personalities, but different modes of God's self-revelation. A typical modalist approach is to regard God as the Father in creation, the Son in redemption, and the Spirit in sanctification. In other words, God exists as Father, Son and Spirit in different eras, but never as triune. Stemming from Modalism, Patripassianism believed that the Father suffered as the Son.
...Tritheism confessses the Father, Son and Holy Spirit as three independent divine beings; three separate gods who share the 'same substance'. This is a common mistake because of misunderstanding of the use of the term 'persons' in defining the Trinity.
...taught that the preexistent Christ was the first and greatest of God’s creatures but denied his fully divine status. The Arian controversy was of major importance in the development of Christology during the fourth century and was addressed definitely in the Nicene Creed.
...taught that Jesus Christ as a purely divine being who only had the “appearance” of being human. Regarding his suffering, some versions taught that Jesus’ divinity abandoned or left him upon the cross while other claimed that he only appeared to suffer (much like he only appeared to be human).
...taught that while Jesus was endowed with particular charismatic gifts which distinguished him from other humans but nonetheless regarded Him as a purely human figure.
...that that the Holy Spirit is a created being.
...taught that Jesus was born totally human and only later was “adopted” – either at his baptism or at his resurrection – by God in a special (i.e. divine) way.
...taught that Father, Son and Holy Spirit together are components of the one God. This led them to believe that each of the persons of the Trinity is only part God, only becoming fully God when they come together.