Divine simplicity is the doctrine that God is a simple entity. The doctrine has been adopted by Judaism, Christianity, and Islam, although it is not universally accepted. It traces its roots back to Greek philosophy. It states that God supposedly has:
- no composition, no divisions or distinctions
- not complex, utterly simple
- indivisible, unchangeable, immutable, no potentiality to be in a different state
- no material substance or matter
- no accidental features
- maximal existence (perfection and goodness), not subject to time
- (according to Aquinas) is existence itself
- is pure act (no potentiality)
It is usually claimed that God does not have these attributes but is these attributes. This supposes God as quite unlike humans and effectively negates any comparison between human and divine thought. Divine simplicity is therefore an objection to the argument from design.
The terminology used in the definition is based on Middle Age ideas and divine simplicity is notoriously confusing. 
Divine simplicity is not explained in the Bible but rather in later theological writings based on Greek ideas. 
Use in apologetics
The concept of divine simplicity is used in various arguments, including:
It is also used to defend against counter-apologetic arguments:
Divine simplicity appears in counter-apologetics:
Intelligence implies complexity
Every instance of intelligence we have experienced is a complex system including a physical body. If God is intelligent, then he also has these properties.
God apparently knows all the past, present and future of all things. He is therefore at least as complex as the universe.
An unchanging entity is not a mind
- "A mind, whose acts and sentiments and ideas are not distinct and successive; one, that is wholly simple, and totally immutable, is a mind which has no thought, no reason, no will, no sentiment, no love, no hatred; or, in a word, is no mind at all."
Divine simplicity "entails that God does not stand in a real relation to creation." 
A simple God would have a single property
- "[this] seems flatly incompatible with the obvious fact that God has several properties; he has power and mercifulness, say, neither of which is identical with the other"
If God is asserted to have multiple attributes and distinctions, theologians must be careful to state this only exists in their minds and doesn't reflect on the nature of God.  The long list of attributes of divine simplicity are side to entail each other and not be distinct. God = good = timeless = knowledge = simplicity = immutable. This is a form of theological cognitive dissonance. "How can diverse concepts be identical when they clearly are not?" 
Nothing is simply their abstract properties
- "No property could have created the world; no property could be omniscient, or, indeed, know anything at all. If God is a property, then he isn’t a person but a mere abstract object; he has no knowledge, awareness, power, love or life. So taken, the simplicity doctrine seems an utter mistake."
Properties do not subsist (self-maintain) themselves, God supposedly subsists. How can a God be identical to his act? 
- "A common claim amongst contemporary theologians is that Christians must choose either the doctrine of the Trinity or the doctrine of divine simplicity. Interestingly, Islamic thinkers in the Middle Ages argued in a similar fashion against the doctrine of the Trinity. [My argument] reinforces these claims."
Apologists try to argue for the compatibility:
- "nor is simplicity inconsistent with the doctrine of the Trinity, for the term simple is not an antonym of ‘twofold’ or ‘threefold’ but of ‘composite.’ God is not composed of three persons, nor is each person composed of the being and attributes of that person, but the one uncompounded (simple) being of God exists in three persons. "
- "God is one being, not three beings. Each Person of the Trinity is in full possession of the One Divine Nature. The persons do not share the one divine nature, it is not divided, it is always one. "
This seems to be special pleading that divine simplicity only applies to God but not the Trinity. It seems to be impossible that the members of the Trinity are distinct if they are each "in full possession of the One Divine Nature".
Incarnation of God
If Jesus, an alleged incarnation of God, was "in full possession of the One Divine Nature", he was also divinely simple. However, this contradicts the Bible account of his incarnation, existing in time, apparently changing in time and having material form.
- "Defenders of divine simplicity must explain how a divine person who is simple can have properties and remain simple. "
Theologians have argued that Jesus had two separate natures, or that the incarnation is a mystery.  This is a fudge to allow changing attributes for God. Does God really manifest itself in pure form or is it always combined with a another nature (like the human nature of Jesus)?
God acquires accidental properties through time
God acquires the properties of Lord, Redeemer based on Biblical events. Therefore he is subject to time and therefore not immutable. 
God is free to make choices
If God is free to make choices, he potentially could take an action and is therefore not "pure act". 
Angels also have some or all these attributes,
God does not have these attributes exclusively. Angels are also similar in nature and undermines the uniqueness of God.
The Old Testament says Moses changes God's mind
"And the Lord repented of the evil which he thought to do unto his people."
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 R. T. Mullins, Something Much Too Radical To Believe: Towards a Refutation of Divine Simplicity, Journal of Reformed Theology 7 (2013) 181-203 
- ↑ 2.0 2.1 Alvin Plantinga, Does God Have a Nature, 1980
- ↑ Bavinck, Reformed Dogmatics, vol. 2, 149
- ↑ 
- ↑ How can the Incarnation be reconciled with God’s immutability? 
- Divine Simplicity, Internet Encyclopaedia of Philosophy