FireLance said:Probably more than 95% of the time, I go by the letter of the rules. I might ignore the letter of the rules under the following circumstances:
1. The rules are inconsistent or have varying interpretations. The spirit of the rules may then be used to determine which variation or interpretation is correct.
2. The rules are unclear. The spirit of the rules may be used to guide the creation of new rules to clarify the existing rules.
3. The letter of the rules results in game situations which the group does not enjoy. Again, the rules may be revised, but the revision would be guided more by the tastes of the group rather than the spirit of the rules.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.