I have covered the more traditional aspects of religion and god in my skeptical entry on "god", but what about the more abstract and philosophical theories out there? Is there any good reason to support theological concepts from a purely logical and philosophical perspective? On balance, I would say no. There is only one thing I have discovered in my many years of investigation which has given me any real reason to think seriously (and, in fact, I still think its the best reason to believe in some sort of god) and that is the so-called fine tuning argument. I will cover this, and several other lines of reasoning, below.
Fine Tuning Argument
This argument points out how well tuned certain physical constants are, and how well balanced certain phenomena are, for supporting life in the form we understand it. For example, there are some major physical constants (see note 1) which determine how the Universe works, and if these were changed even slightly we would not have a Universe which has turned out to be as suitable for life as this one has. A less compelling argument covers factors such as the size of the Sun, distance of the Earth from the Sun, size and location of Jupiter, etc.
At first look its hard to see the flaw in the logic of this argument. If these major constants could have had any value at all, and if other values would have produced a Universe which couldn't support life, its not unrealistic to suppose the values were set the way they were in order to make a Universe suitable for life. If the constants were set that way then who did it? Anything capable of changing the value of physical constants in order to achieve a specific outcome deserves the label of god, surely.
But when you look at the argument more deeply its not quite as clear. First, this is an argument which argues the cause based on the final result (see note 2). In other words, we are asking what are the chances of something happened when it has already happened. Its like winning a lottery and asking "what are the chances of that happening". Well, since its just happened, the chances are 100%, actually!
Second, why should life as we see it today be the only possible ultimate purpose of the Universe? If the Universe had been different there might be life in a completely different form than we have today, or no life at all but something else of equal value (and this value is subjective anyway). Again we are taking an end point and arguing it is the only possible ultimate reason for existence.
Third, its also partly at least an argument from ignorance (see note 3). Admittedly, we don't know why the constants are the way they are, but that ignorance doesn't mean we have to invoke god as an explanation. In the past we have used got to explain the diversity of life. We now don't need to because science can explain it. The same is true for many other phenomena. Maybe in the future we will increase our scientific knowledge to the point where we can explain this phenomenon, as well. Ultimately we would expect science will be able to explain everything (although there's no proof of this).
A theory which was originally treated as being on the genuine edge of science, but is now gaining favour is the idea of a multiverse. Its possible that the Universe we see is only one of many, perhaps an infinite number, of Universe, all with different physical properties. If this is true its certain that one of these Universe would have the characteristics for life as we know it. That Universe is the one we live in, we know that, of course, because we're here! There is some evidence supporting this idea, such as the similarity between the phenomena of black holes and the Big Bang. This is a very preliminary theory but it hold some promise and would completely invalidate the whole idea of the fine tuning argument.
Of all the arguments supporting god (in the widest sense) I find this one the most convincing. But it is still effectively a "god of the gaps" argument so I can't take it too seriously without supporting evidence. Therefore I give this a moderate score on the crap-ometer.
1. Which constants are important enough to be considered fundamental to the Universe's operation varies depending on the exact argument being considered. For example, in the book, "Just Six Numbers", Martin Rees lists these: ratio of the electroweak to the gravitational force, constant related to the strong force, the number of electrons and protons in the universe, the cosmological constant, the ratio of fundamental energies and the number of spatial dimensions. It doesn't matter which constants are used though, the basic argument stays the same.
2. The rejection of this argument relies on a large, or infinite number of possible Universes. The fact that the one we are in suits us "perfectly" is because that's the only one we could be in and be able to ask the question.
3. An argument from ignorance, or argument from incredulity, is a logical fallacy which states that something is true because there is insufficient evidence to show its false, or vice versa. Therefore saying a theology is true because there's not enough evidence to support an alternative scientific hypothesis is using false logic.
Sources of Further Information
There are many web sites with information on this subject. Below I have shown some which present the information for both sides of the argument.