antipassive and anticausative

I cannot follow the sprit of how linguists have made up the terms Antipassive and Anticausative.

Anyway, I know that both have one thing in common: a promotion.

In case of an ergative language, an antipassivization operation is fulfilled by deleting the object(P), and by promoting the ergative case marked Subject(A) to the new S.

In case of an accusative language, an anticausativization operation is fulfilled by deleting the subject(A), and by promoting the accusative case marked object(O) to the new S.

well.....still complicated lol