So God*: Can he sin? From what I've noticed this argument tends to proceed as follows:
Theist: God is perfect, he cannot sin - ergo, he does not lie, murder, steal, etc.

Skeptic: But God is all-powerful! What? You mean, he ISN'T ALL POWERFUL BECAUSE HE CAN'T LIE? OH YEAH TAKE THAT RELIGIOUS IDIOT.

Theist: Uh, oh, uh, shit. I mean, ok look: God is PERFECT, so it is not that he lacks the capacity to sin, just in his perfection he never would. While these are contingently identical situations, the inability to sin and the unwillingness to sin are meaningfully distinct enough that I consider this a solution to your question.


Now, despite my somewhat cheeky portrayal of the Skeptic**, I do agree with his general point: That there is something wrong with this notion that God cannot sin. However, I also have to agree with the theist: God cannot sin. But, I think, God can lie, murder, steal, or do anything he can (which, by definition, is everything).

Let me explain:

We have to start by defining what it means to "sin". In more technical terminology, sin is a theological term for normative failing: That is, falling short of normative standards. For those of you unfamiliar, normative standards are best understood as moral standards stemming from a JUSTIFIED source that carries the authority to actually determine rules of behavior: They are what one "ought" to do. So, if one "ought not steal", it is normative consistency not to steal, if one does steal, they have committed a normative failure - that is, done what they "ought" not do. This is a sin.

For humans in a theological universe, this is fairly straight-forward: God is the creator of the Universe, and you and so he gets to set normative standards (taking away the trickier question of "is there such a thing as normative judgement?" Since we're talking theology here, we'll say there is and God gets absolute control of them). Thou shalt not murder, thou shalt not stick it in your neighbor's daughter, etc.

If you follow these rules, you're a normative success. Fail to, and you've breached what you "ought" to do, and you've sinned. Since God is just, he punishes sinners - those who did what they ought not to have.

If you're following thus far, you probably have this basic mental sketch: Morality, in normative standards, is some sort of line or shaded area defined by some source (God, here). If your actions fall on the line or in the shaded area, you're being moral. If they fall out, you're not. One's own moral standing is determined by HOW CLOSELY THEIR OWN BEHAVIOR MATCHES THE MORAL LINE/AREA. A one-to-one match, obviously, is perfection.

Now, lets talk about God: at this point, the picture becomes a little bit less certain, but it also brings about how I think God gets to be a lying, stealing murderer and still be "perfect".

My argument is this: God creates normative standards. In fact, he doesn't just create them: he IS them. When one says, "God is good", it isn't meant synthetically: that is, God doesn't happen to have the characteristic of goodness, rather, it is, for more religious people, definitional: God IS good, and good IS God: they are one and the same. God created the Universe, its rules, and Lords over all of it. What "Good" is is defined by him: for their to be a set of normative standards outside of or above God would be to contradict the premise that God is the original and supreme being.

This leads to a simple conclusion: Any action God takes is morally correct. If normative success is judged by approximation of behavior to the normative zone, then God - as the normative zone itself - cannot be anything but a perfect success. A sin for God's children to kill but not for God to kill? Sure: if God has it that way, that is the law. God says he won't lie one minute then lies the next? Again - you cannot, strictly speaking, call this anything but perfection unless as a religious person you are prepared to dispute the notion that God's judgement and will are supreme: unless you want to say, essentially, that God doesn't get ultimate say over moral law and that God can be wrong. The notion that the rules for God are different from those for people is obvious on its own (think of parents and children, or that jealousy is a sin but God admits to being a jealous God), but taking a step further I see not theologically consistent way to defend anything but the position that any action God takes is morally upright by definition.

In short: No action can be deemed a normative failure by the being whose behavior is definitionally associated as the standard of normativity.

*Judeo-Christian God, obviously.
** For the record, I do not believe in God. I simply intend this as a logical exploration with some pre-determined assumptions (those of the standard beliefs about God in western religion).

*** For deduction buffs, here's that whole rant in an easier to follow form:
(i) Normative standards are strictly defined such that for every p some action x either is consistent with p or inconsistent with p.
(ii) Inconsistency with p is deemed normative failure, and consistency with p normative success.
(iii) God created everything, is the original being, and his judgement is supreme and original.
(iv) By (iii), God created normative standards and is their justifying source.
(v) By (iv), Any x(god) is p, when all p are defined as x(god).
(vi) No x can be both p and not p.
THEREFORE
(vii) All actions by God are normatively upright by definition.