KaeYoss said:
Personally, I equal "cleric" to "worshipper of a deity".
I wouldn't say that, KaeYoss... one thing is to worship, another is to actively serve a cult and possibly increase the number of worshipers.
However, your view is perfectly in line with the base D&D idea that Clerics are granted powers from their deity. By this view, a godless cleric should simply have no divine powers.
If the DM simply says that a cleric takes his powers from his own faith (whether he believes they come from an actual god or not), it doesn't matter anymore if his deity really exists or not.
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I actually think that the idea may be a balance issue, divine casters usually have an easier time (they can wear armor, they know all spells they can cast) and stressing the fact that their deity may cut off their magic powers if they "misbehave" could be an attempt to balance them against arcane casters. Removing this limitation can make a cleric too easy, and perhaps this is the reason why this is a constant thing in D&D books?
However, I think the open option of deities not related to a single deity is important for the DMs who want a different approach to religion in their settings. Even if the options immediately let us think of clerics of NO deities, I think its best application is for clerics of MORE deities, like an Elf cleric of the whole elven pantheon.
If the option allows a player to play a cleric with no moral bias (imagine a Neutral cleric of no deities... what the hell is he?

), well that's not much a "cleric" after all, since being extremely biased towards something IS being a cleric at all, and the player is simply roleplaying very badly...