necessarian

An adherent of necessarianism; an advocate of the doctrine of necessity.

1810, Charles Buck, Materialists, entry in A Theological Dictionary, Volume 2, page 86, And the Necessarian asserts, that if, in any given state of mind, with respect both to dispositions and motives, two different determinations, or volitions, be possible, it can be on no other principle, than that one of them should come under the description of an effect without a cause; just as if the beam of a balance might incline either way, though loaded with equal weights.

But neither you nor myself, necessarian as I am, can pretend to this degree of perfection.

Alternative letter-case form of necessarian.