Quite often, theists posit arguments, but when they are met with difficulties, they necessitate extra premises. This is the case in Glenn Peoples' Moral argument, as pointed out by
Stephen Law on his blog.
Here is what he had to say about what this does for the likelihood of the argument then being true:
Glenn Peoples' blog has been interesting me lately. He has just out up his version of a moral argument for the existence of God.
Glenn argues, as does Craig:
If there's no God, there are no objective moral values. There are objective moral values Therefore there is a God.
Of course, Glenn realizes his premises, especially the first premise, will require considerable support, so he makes his case for it here.
Here's part of my comment on People's moral argument...
Glenn – I’m tempted to start investigating your argument more but it would be really helpful if you could set out the argument more formally, so that the most basic premises supporting your conclusion are clearly identified. Make it very clear why there is objective moral value only if there is an all-powerful, all-good, personal God. E.g. why moral Platonism won’t do, for example. Why non-natural objective moral facts won’t do either. Why it’s got to be a person. Exactly how the is-ought gap plays a role in delivering the conclusion. It would also be good to see what your assessment of the probability of each of the basic premises of the argument is.
Notice by the way that as more premises are introduced that you may consider to be much more probable than not – that have, say, an 80% probability of being true – the probability of your conclusion being true may nevertheless drop like a stone. With, say, just five required basic premises of 80% probability each, the probability that your conclusion is true drops to just 32%.
That’s to say, the probability that your conclusion is FALSE is nearly 70%!
(Wes Morriston also points this out, I believe)
However some theists (not you, I’m sure) are very good at disguising this problem of plummeting probabilities with amazing rhetorical flourishes!