The information given on this page is assumed to actually be part of the Wish spell, as a lengthy warning and guideline on how to use the spell. Any wizard who can cast Wish will be aware of these rules, although this may not be the case if you are granted a wish by a djinn or magic item.
The general principles of a Wish are as follows:
- The potential energies summoned by a wish are not unlimited; however, they are exceptionally vast, even beyond the power wielded by other 9th-level spells.
- Wishes are only 9th-level spells, and their power is limited. The greater in magnitude the wish above the power of a 9th-level spell, the less stable and safe the wish.
- Wishes cannot change what has already happened, but they can be used to alter or negate the result of some prior happening.
- Wishes cannot directly affect what will happen, except in the sense that everything that will happen is a result of what is and has been happening.
- Wishes have no power or authority over the abstract, the non-concrete or the theoretical.
- Wishes cannot create magic items from thin air, although they can pluck them from elsewhere.
- Wishes cannot change a person's true alignment, feelings or personality. They can, however, charm, curse or enchant them.
- Wishes cannot create a soul, although they can create life with a natural or elemental spirit (similar to a fey).
- Wishes will follow the path of least resistance while abiding by the wording of the wish itself.
- Wishes will almost never achieve more than one specific end. The word "and" does not make one wish into two.
- Wishes are objective, impartial, and consistent.
Wishes that outright break any of these principles will not be fulfilled, and have no effect. If you try to change the past or future with a wish, for example, it will not have an unforeseen consequence. It will simply do nothing.
As noted in the spell description, certain "easy" wishes do not weken you when cast. These include teleportation or planar travel, complete healing, or the raising of the dead. Other wishes, though they will debilitate the caster, are relatively safe. Wishing for 1,000 to 10,000 gold pieces worth of treasure or destroying a creature within sight of 10 HD or less are both fairly easy to accomplish with a wish.
As noted above, although vast amounts of energy is harnessed by a wish, this does not necessarily mean that this energy can be controlled. The more extravagant and powerful the desired effect compared to a "normal" level 9 spell, the less stable the wish. "Normal" level 9 spells can summon creatures from other dimensions, reverse gravity in a local area, change your true shape, or place someone outside of the flow of time itself. This is the level of power that the DM should keep in mind when adjudicating wishes.
When we say that an overly ambitious wish becomes less "stable", we mean that it becomes more literal and less true to the spirit of the wish. Wishes that are equal to the power of a level 9 spell are almost never "creatively interpreted" by the multiverse. Those that are not, however, may have very different consequences to those intended by the caster. The more extravagant, the more difficult it is to avoid unforeseen results. The spell, being unable to fulfill the intended meaning of the wish, will try to find the path of least resistance among literal, figurative and metaphorical meanings. It will start to bend the meaning of the wish until eventually it comes out with a solution that technically works, even if it in no way resembles what was originally wished for.
For example, if you wished for a kingdom, it is unlikely it would simply appear as you desired. Depending on the circumstances, you might receive the local ruler's crown, or you might change to resemble them exactly. You might have a castle spring from the ground, fully outfitted and armed - but this doesn't mean that the local ruler will tolerate your presence. You might receive knowledge of a secret and untouched valley ripe for conquering, or the location of an artifact that could give you an army of ghosts to command. But it is unlikely you would simply become a king.
"I wish to be invincible."
How is this adjudicated? To answer this question, you must consider one of the principles above: "Wishes will follow the path of least resistance while abiding by the wording of the wish itself." Open-ended wishes such as this can be particularly dangerous, because they allow the wish complete discretion as to how to achieve your end. Being made permanently ethereal would make you invincible to normal weapons, but would come with a hefty price, for example.
If you're looking to wish for something big and powerful without having something bad happen to you, open-ended is not the way to go. You should be as specific as possible, while using as few words as you possibly can to minimise the room for confusion.
In addition to the stipulations given above, there is a special rule for increasing ability scores with wishes. Any attribute can be increased to 16 with a single wish. After this, each wish expended will improve a stat by 1 point. Of course, you can wish for more dramatic increases ("I wish I had the strength of a giant"), but they will not be permanent.