When I was a child, I used to pray to God for a bicycle. But then I realized that God didn't work in that way--so I stole a bike and prayed for forgiveness
--Emo Philips, comedian
Whatever a man prays for, he prays for a miracle. Every prayer reduces itself to this: Great God, grant that twice two be not four.
--Ivan Turgenev, novelist
Supplication has got to be the mostly widely practiced superstition in the world. Millions of adults believe that murmuring some words or even silently saying them in their head has the power to make their wishes come true. I think one reason why prayer is so prevalent is that it's a vast "improvement" over the childhood belief that what I want to be true will become so simply because I wish it to be so. In this "new improved version" of that infantile belief the agent that makes one's wishes come true is no longer the "I," rather it is a transcendent "I", an anthropomorphic being who has been vested with far greater powers or even (peri) omnipotence. What started out as "what I say will be so" has been transformed into "a superagent who is outside of me hears my thoughts/words/desires and will make my wishes come true." In effect one has conjured up a personal (invisible) genie.
As with other superstitions one mechanism (but not the only one) that keeps the belief in prayer alive is the existence of actual positive correlations, even if such correlations are sporadic and infrequent. Given the millions of prayers uttered in the world each day there will be a number of entreaties that will apparently be answered. Because the correlation is interpreted as a causal relationship it is a post hoc ergo propter hoc fallacy. (Even very strong correlations do not necessarily imply causation. Suppose every time after clipping my nails I implore a certain god to make them grow back in a week. Does the perfect positive correlation between prayer and nail growth mean that prayer works and that there exists this particular deity that causes nails to grow a couple of millimeters every week?) The questions and experiments that don't get asked and done are: What if the prayers hadn't been transmitted? Would the results have been the same/different? What if we want K but prayed for the opposite? Would K still have transpired?
Given the law of large numbers it would be most miraculous if no coincidences (apparent successes) occur. Such coincidences are to be expected (not least because, among other things, what counts as success and the time frame within which it's suppose to happen are not clearly specified). This is similar to the occurrence of supposed precognitive dreams. With the billions of dreams per night, it is certain that a few of these dreams will "come true." Again, what would be most incredible is the situation wherein there are absolutely no matches between what are dreamt of and events thereafter in the real world
Throughout our life we have heard over and over implicitly or explicitly the claim that prayer works, that this or that deity hears and answers prayers. The biggest problem with this ubiquitous claim however is that there is no good evidence that it's true. On the contrary, there is a litany of anecdotal evidence and a host of scientific studies that show the opposite is the case--that prayers don't work. But because we don't receive news reports of the millions of prayers that weren't answered and given that what we do hear from media or from friends and family are the few stories of wishes that were supposedly granted, the availability error kicks in. There is the tendency to think that the effectiveness of prayer is real because we hear (and remember) the success stories, but hardly hear of the much much larger number of stories of failure.
Closely allied with the availability error is the biasing condition of vividness. When we hear success stories of prayer resulting in such wonderful miraculous events we tend to remember these highly inspiring/motivating/emotional stories. The more vivid the anecdotes the more they tend to get imprinted in our memory, and the more they serve as among the bases for judging the efficacy of prayer. Furthermore, an ardent believer will be biased toward selectively remembering his/her own personal anecdotes of successes while brushing away or even forgetting instances of failure. Confirmation bias then becomes a way of supporting their belief in prayer.
Like having a lucky rabbit's foot or lucky shoes, the intriguing thing about prayer is how rationalizations are immediately sought and manufactured when the desired result fails to materialize. If the horse I bet on loses the race then perhaps I didn't shine my lucky shoes well enough today, or maybe the chain wasn't slung around my neck just right for the amulet to be centered on my chest. As for petitionary prayers, when cognitive dissonance is experienced (i.e., when prayer undeniably fails to result in what is desired) rationalizations of sorts are offered to explain away the apparent failure. And to me the following (illicit) ad hoc explanation wins hands down: "God always answers prayers, but sometimes he says no." This is a "win-win" rationalization since whether praying results in success or failure, the core belief in the supernatural and in the power of prayer remains intact. With this ad hoc explanation the claim that God hears and answers prayers becomes nonfalsifiable, irrefutable. It conveniently explains away all failure and is thus a most effective way in keeping the belief forever immune to disconfirmation. Of course, when asked how they know that there is a deity (and is the kind they believe in and not the deity of another religion) and one who sometimes doesn't grant what is wished for, some believers may use the fact that some prayers fail to result in what is wished for as their evidence. When it's pointed out to them that that's circular reasoning, they might then start a frantic search in their sacred text. When pointed out to them that there is no evidence that any of the theological claims in their text are true, they sooner or later fall back on the ultimate back door: "You must have faith!" And when pointed out to them that belief however strong does not make something true they just might ...
I don't expect belief in prayer to disappear anytime soon. It frequently is a last resort for people. Desperation can drive us to the edge. We can become irrational and clutch onto anything, even a delusion. But as in the case of amputees, the whole world can pray everyday for the next thousand years but no lost limbs will ever be restored.
Here's what Heather MacDonald has to say about entreaties to the one on high.
...I had started noticing the puzzling logic of petitionary prayer. What was the theory of God behind prayer websites, for example: that God is a democratic pol with his finger to the wind of public opinion? Is the idea that if only five people are praying for the recovery of a beloved grandmother from stroke, say, God will brush them off, but that if you can summon five thousand people to plead her case, he will perk up and take notice: "Oh, now I understand, this person's life is important"? And what if an equally beloved grandmother comes from a family of atheist curs? Since she has no one to pray for her, will God simply look the other way? If someone could explain this to me, I would be very grateful.
I also wondered at the narcissism of believers who credit their good fortune to God. A cancer survivor who claims that God cured him implies that his worthiness is so obvious that God had to act. It never occurs to him to ask what this explanation for his deliverance says about the cancer victim in the hospital bed next to his, who, despite the fervent prayers of her family, died anyway.