I don't think that theism is necessarily irrational.
When I hear that religion/supernaturalism is 'irrational' it doesn't seem right to me. A lot of others agree with my sentiments and the kneejerk reaction is to try and give reasons for supernaturalism. In my opinion, this always ends in failure because the arguments don't hold under scrutiny. But even afterwards, calling supernaturalism irrational doesn't seem right, especially when you talk to believers in it.
Dawkins and others will say that this is because many of them are rational in every other way so the impression of rationality sticks, even when they turn it off. The thing is, these supernaturalists are still trying to apply the same reasoning to their supernatural beliefs, even if their reasoning is flawed.
I think I can sum up my argument as follows:
This time last year it was rational for me to believe in God, but it wouldn't be now.
Or; Descartes' belief in the supernatural was rational but it would not have been rational for David Hume to hold such a belief.
My definition of rational/irrational is as follows:
To act rationally is to act upon reasoning and act irrationally to act in the face of reason. So how can the same act be rational for one person but not for another? If both people have applied their rationalilty to the best of their abilities and come to different conclusions then both will be rational in their differing acts.
Notice that I'm not judging by how advanced/precise their reasoning is but more their attitude to it, that they genuinely tried to reason as honestly as possible. So I think that Descartes' proofs of God were flawed, but he was still rational for following them.
Argument against reductionism/positivism
One argument I hear for theism being irrational is that people should only believe in things that have been proved. Not quite those words but something to that effect.
I think this the correct approach for bodies of scientific/historical/philosophical knowledge but is in appropiate for personal beliefs.
We don't start with refined rational methods.
Our learning process is long and drawn out. I've heard somewhere that one isn't capable proper critical thinking until they reach teenage. Either way, our refinement of logical methods is an on-going process. The consequence of this is that by the time we are capable of the standard of reasoning that these positivists demand, we already have a large body of disorganised knowledge. Should we now start from scratch using purely logical methods?
Or do we go about the task of re-organising the knowledge we have?
I think we do the latter.
Do we go about re-organising all of it?
I think that's as impractical as it comes, and unnecessary.
What we do is we find beliefs that are problematic and use our methods of reasoning as a kind of therapy to clear up confusion.
So rather than the positivist picture of; "I believe in things that I have come to rationally", I think the "I have applied reasoning to clear up problematic beliefs" is a more accurate way the way we think.
In my case, I had reasons to believe in God about a year ago.
They weren't very clear and concise reasons, probably went something like this:
1) Life sometimes seems written as a story, as if it was meant to be this way. (like there was a designer making things happen) I was quite a believer in fate.
2) The worldview containing God seemed to work and be coherent. It also seemed intuitively right in a lot of ways. It 'felt' right.
3) I saw something very special in the religious people. Their faith gave them a distinctive character and made them the kind of people that I saw close to ideal in a lot of ways.
Since the topic has come up, I've found myself putting these reasons through more advanced analysis and I gradually found them to fail. I no longer see these as good reasons to believe in a God, that all these 'gut feelings' have more natural explanations and such 'feelings' can sometimes be misleading. (I still declare my gut to be 90% accurate on most issues! )
My point is, the positivist/reductionist has argument along the lines of:
1) If someone is justified in believing God then they need a rational reason
2) All reasons I've come across have failed
c) Theism is irrational
If the believer don't know (2), i.e. hasn't worked out that their reasons fail then they have every reason to believe that their reasonings work. So they're not going against reason in following the conclusions. It would only be if they knew that their reasonings failed and still followed the conclusions despite this that they'd be irrational.
So why don't I like the word 'irrational'?
I've so far argued that saying "theism is necessarilly irrational" is technically correct.
Now I'll try and explain why I think it matters.
'Irrational' is a bit insulting. It accuses the person of not thinking.
The common use is in an everyday argument, usually when one side is getting a bit hysterical; "you're being so irrational! You've got no reason to believe..."
Theists might've gotten something wrong in their reasoning, but many of them have thought things through carefully and used their knowledge as effectively as they can. Calling them 'irrational' is kind of rude, saying it's as if they hadn't tried at all. The other thing that winds people up about that word is the name-caller can often be a kid who's read one Dawkins book and starts laying into someone who's thought about the issue a lot more. It's why so many people roll their eyes when the 'I' word is used and in some cases is seen as the atheist equivilent of 'burn in hell' jabs.
In my experience, this name calling makes people defensive and less open to atheistic arguments. If the arguments had been presented to them in a more rational manner (i.e. appealing purely to the listener's sense of reason without name calling and/or pressure to accept) then they would gradually have come to find them undeniable. As they gradually came to understand the arguments better then they'd find they make perfect sense. When you make people defensive it discourages this and they becoming more interested in 'saving face' and finding an answer of some sort, because they don't appreciate their reasonings being insulted and don't want to give you the satisfaction of being right.
I've never been convinced of something during the argument.
All the arguments that have changed my mind took time to do so.
Rather than be instantly proved/disproved of something, I'd come to understand the argument and come to consider it flawless, that I had no answer against it. (well, maybe not flawless but strong enough to convince me for now - I still consider all these arguments open to question! )
I think that adequately voices my views on this topic.