Lisa asked:

How can moral monotheism be proven wrong through the following premises:

an action is right if, and only if, God commands us to perform it.

God is the ultimate moral author.

Which actions are right is not arbitrary, but objectively valid.

By what means can I prove this wrong and state there is no God?

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There is a philosopher's problem called the Euthyphro dilemma which is about this. Either of the
following must be right:

1. x is good because it is loved by the gods

2. the gods love x, because x is good

So you conclude that either the good is commanded by the arbitrary whims of the gods, or else the
good is external to whatever desires and proclivities the gods may have.

I don't think the Euthyphro dilemma amounts to either a proof or disproof of whether or not there is a
god. But it does lead to certain conclusions about the nature of God. For example, if what's good is
decided arbitrarily — or if the gods simply decides what should be good — then this leads us to think
that we can morally assess the gods. Surely if the gods decide that pain and suffering are good then
we can morally assess whether this is right, and morally judge the gods.

On the other hand, some people think that there could only be an objective morality if there were a
god to dictate what is right and wrong. If this is the case, then there is a problem with the second horn
of the Euthyphro dilemma; if the gods have tomeasure upto a standard of goodness external to their
whims, then why introduce the gods as a guarantor of objective morality?

From this, you kind of conclude that the gods must decide what is morally right,but at the same time
conclude that the gods can act in an immoral way. It seems to me that theists who try to ground an
objective moral system on religious belief are in something of a cleft stick here; either there is no
need to postulate god because morality is external to his whims, or you have to accept that prima
facie immoral activities are alright because God decided they would be.

At the very least therefore, the dilemma might make you suspicious about grounding morality in
religious belief. Of course, you might respond as Descartes does and say that by definition God could
never fail to be perfectly good, and avoid the dilemma. But that is much too close to cheating for my
taste.

Adam Gatward