Arianism



Arianism is a view of the Trinity where Jesus is a created being, rather than being one with God; it is not to be confused with Aryanism and has nothing to do with Nazis, except those poor at spelling. It is named for Arius, a Christian presbyter from Alexandria, Egypt who lived from c. 250 AD to 336.

Arian Christology
Arianism considers Jesus distinct from God the Father, having been created by him, but nonetheless describes him as Lord or Master, while denying that he can know the Father fully. The Arian viewpoint on the Holy Spirit is that it is a "sanctifying power," subordinate even to the Son. They point to such scriptures as and  in support of their claim that Jesus is distinct from the Father, and  and  in support of their claim that he was created by God.

They contrast with the mainstream Christian belief that the Father and Son are "homoousion", i.e. of the same substance (from the Greek for same substance or essence), as used in the Nicene Creed. Arians held various opinions on what Jesus was made of: homoiousians believed that the two were of similar but not identical substance; homoeans believed they were similar but not of the same substance or essence; and heteroousians held that they were different in substance or attributes. The last included anomoeanism, the belief that Jesus's nature was neither the same nor similar to God's, a belief held by Aëtius "the atheist" of Antioch and others.

It's not clear what difference this made in practice, but there's very little idea of what Arians believed. The theoretical questions were things like, did Jesus always exist or did he appear/get created at some point (the latter is Arian); and was Jesus equal to God (because made of the same stuff) or subordinate. None of this impinges on actual moral or ethical questions.

History
Arianism is very fourth-century, and the Council of Nicaea (325 CE) threw it out as a belief-system. Arius himself was exonerated in 335, and his teachings enjoyed the support of the next two emperors. Finally, the First Council of Constantinople in 381 anathematised Arius again (posthumously). Despite all the Orthodox condemnation floating about, Arian teachings have resurfaced occasionally since then, including among Germanic tribes (notably the Goths) in the early Medieval period, and recently in the Yorkshire-based Holy Catholic and Apostolic Church of Arian Catholicism.

Jehovah's Witnesses, though sometimes characterised as modern-day Arians, only describe the Son as having been created by the Father - they do not share the remainder of Arius's beliefs. Mormonism can also count as Arian, as it views Yahweh and Jesus as distinct entities.