The typical presentation of a god in fantasy games assigns various spheres of influence to the god. In D&D 3 and Pathfinder the gods have associated domains.
Two tenets and one more
Each cleric, or other character drawing power from a more powerful being, writes two tenets. The referee must accept the tenets. Each selected tenet must be connected to a different domain associated with their patron god.
If the cleric chooses particular domains, then each chosen domain must have one associated tenet. Typical cleric selects two domains and so should write tenets related to those.
A tenet restricts the behaviour of the cleric, at least in some situations.
Each cleric also has the common tenet: to respect the god and what is sacred, to avoid what is profane, to participate in the daily rites and prayers, to be subject to the rituals associated with birth, death, coming of age, marriage, justice, etc. For monotheistic religions this tenet also includes not serving other gods.
Example: Tenets of Absolon
Though tenets are particular to a given character and god, some suggestions or defaults are useful.
- Glory: Destroy the undead and the unholy, as well as mortals consorting with such. Should this be beyond your present ability, harm them as much as you can and return with greater force.
- Law: Expand the influence of Absolon, i.e. the laws and customs of the empire of Maldor.
- Nobility: Treat nobles according to their station.
- Aristocracy: Act and demand to be treated as one of noble blood. To select this tenet the character must be a member of a noble house in Maldor.
- Leadership: Take leadership over your peers and inferiors, as defined by the hierarchy of the church of Absolon and empire of Maldor.
- Sun: As the sun settles, call it back and keep its memory with an open flame; a campfire or more if you remain at a fixed location, a torch or greater flame if you are on the move.
- Day: Act during the day, rest during the night.
- Light: Never be in darkness.
Breaking a tenet accidentally, in a minor way (it is not noticed in play when it happens, only later), or against your will has the god choose some of your spells for you when you next prepare spells. The chosen spells should reflect the personal failing, rather than punish.
Acting against the god or breaking a tenet leads to the god withdrawing a measure of its power: the cleric loses their spells of highest level until they stop breaking the tenet. A full day of respectful obedience gives the powers back, as does using the atonement spell.
Denying the god, blasphemy, or severely breaking a tenet leads to immediate loss of divine powers. Repeatedly breaking a tenet, despite the warnings, leads to the same. Only an atonement may return the divine favour.
Altering a tenet should follow the same guidelines as changing alignments, but should not be as big a deal. A ritual of some sort is also appropriate, or an atonement spell. The referee must accept the new form of the tenet.
The referee should always warn the player that their character is about to lose their divine powers, if such an event is about to happen. An act done without knowledge may only lead to the lesser consequences.
If a character is about to break a tenet or considers such an act, the referee should roll an easy check of wisdom or religious knowledge and, on success, warn the player of the consequences.
A player who asks about the divine consequences of an action should get an answer, possibly conditional on a check of wisdom or religious knowledge. The check should not, in general, be very difficult. Even low level divine spells (guidance, augury) should warn of divine disfavour with no chance of failure.
The tenets are supposed to be somewhat restrictive, but not crippling, so they change gameplay without making the cleric unplayable. This is hard to tell without playtesting, but similar reasoning applies to selecting and defining BITs in Burning Wheel, keys in Solar system, etc.
The purpose of these rules is to emphasize the role of religion for adventurous religious characters and to make clerics of different faiths different in their behaviour. The ability to choose a number of tenets may mirror various factions among the faithful, and allows for greater freedom and more restrictive tenets that do not completely define or cripple a character.
The tie to domains or spheres of influence provides a starting point for defining the tenets, as well as a fixed number for their amount.