Self-existence

Aseity (from Latin a "from" and se "self", plus ) is the property by which a being exists in and of itself, from itself, or exists as so-and-such of and from itself. The word is often used to refer to the Christian belief that God contains within himself the cause of himself, is the first cause, or rather is simply uncaused, though many Jewish and Muslim theologians have also believed God to be independent in this way. Notions of aseity as the highest principle go back at least to Plato and have been in wide circulation since Augustine, though the use of the word 'aseity' began only in the Middle Ages.

Aseity has two aspects, one positive and one negative: absolute independence and self-existence. In its "negative" meaning, which emerged first in the history of thought, it affirms that God is uncaused, depending on no other being for the source of His existence. In its "positive" meaning, it affirms that God is completely self-sufficient, having within Himself the sufficient reason for His own existence. The first concept derives from "the God of philosophers", while the second one derives from "the living God of Revelation" (I am who I am: Exodus 3:14).

As a part of this belief God is said to be incapable of changing (see Hebrews 13:8) Changing implies development. Since God was, and is, and is to be the Absolute Perfection, there is no further need to change: he is αὐτουσία (unchanged: Gregory of Nyssa),actus purus and ipsum esse subsistens (Thomas Aquinas).

Many (St. Thomas, for instance) have also thought that aseity implies divine simplicity: that God has no parts of any kind (whether spatial, temporal, or abstract), since complexes depend on their individual parts, with none of which they are identical. Classical theists have often drawn a further implication: that God is without emotion or is "impassible": because, it is said, emotion implies standing as patient (pass-) to some agent – i.e., dependence. This is so because, although God has created everything, He is not in dependence on His creation.

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