First, Pascal assumed that one could not use reason alone to determine if God exists, but rather must make a decision to believe or not to believe. (I object to this assumption on two grounds - first, that we may indeed use reason to rule out many definitions of God, and second, that one cannot necessarily *decide* to believe in or not believe in God. However, that's outside the scope of this post.)
Based on this assumption, Pascal argues that we should make the most rational choice, which can be thought of as a wager. The choice may be best represented as a matrix:
|God exists||God does not exist|
|Wager for God||Infinite reward||Insignificant relative to infinite reward/punishment|
|Wager against God||Infinite punishment||Insignificant relative to infinite reward/punishment|
Now this of course makes a number of suspect assumptions which are also outside the scope of this post, particularly that God will reward those who choose to believe or act a certain way merely to achieve Heaven or avoid Hell.
However, the part I would like to focus on is God. If Pascal's Wager is to work, we must know which God to follow! Surely Pascal had in mind the Christian God, but the wager doesn't work if we pick the wrong God. In order to make the most rational wager, we must look at all the potential gods.
There are several questions we must consider. First, we may estimate a probability for each religion being the correct one. Second, we may compare all the various Heavens and Hells to see if some are better than others. Third, we may compare the various religions to find Gods which are more tolerant of those who believe in the wrong God. Finally, we must consider how likely it is we will succeed in pleasing a particular God if we try our best.
How may we estimate the probability of each religion being correct?One possibility is to simply create a ratio of followers of each particular religion over all believers. Some religions may be combined while others must be separate. For example, if being either an Anglican or a Catholic will get you in the same God's good graces, we may safely combine them. However, if being a Mormon will get you in trouble with the Catholic God and vice-versa, we must consider them separately. A simple ratio doesn't seem like a very accurate measure of probable correctness, but it may be the only measure we have, if we're assuming (as we are) that one cannot use Reason to determine if a given God exists.
Heaven and HellWould you prefer 72 virgins or an eternal beis midrash? Harp music or nirvana? While any eternal Heaven may serve as "infinite good" for the purposes of our wager, we might have a personal preference for one over another. Everything else being equal, we should pick the religion with the most appealing Heaven. Similarly, not all Hells are equal. We can certainly rule out those religions with limited or no versions of Hell (sorry Orthodox Judaism and Buddhism.) We must avoid the worst Hells we can. To me, the Catholic (and certain other branches of Christianity) Hell seems by far the worst and most eternal.
Is a God Tolerant of Non-adherents?We may safely throw out all the Gods who are tolerant of non-adherents, since we need not fear following the wrong God if He is the correct one.
How Hard is it To Please a God?If we decide that we like one God's Heaven the best and fear His Hell the most, we still have to consider whether we will please Him if we try. If, for example, we will never please Him no matter how hard we try, there's no sense wagering on Him, since we'll be screwed either way. I would rule out Jehovah's Witnesses, for example, since their God only allows 144,000 people into Heaven and I don't like those odds. Certain other religions have exceedingly difficult standards, and others still are impossible to succeed in without having been born a certain way.
ConclusionBased on careful consideration, I recommend a branch of Christianity which has 1) a large number of followers, 2) a very good Heaven and a very scary, infinite Hell, 3) an intolerant God, 4) and a relatively easy path to Heaven. For example, a Christian denomination that demands only that you believe in Jesus seems perfect.
So Pascal's Wager (assuming we agree with its basic assumptions) is only a bad religious argument if you're arguing for a different religion.