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In page Modal logic:

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K through S5 form a nested hierarchy of systems, making up the core of normal modal logic. But specific rules or sets of rules may be appropriate for specific systems. For example, in deontic logic, ◻ p → ◊ p {\displaystyle \Box p\to \Diamond p} (If it ought to be that p, then it is permitted that p) seems appropriate, but we should probably not include that p → ◻ ◊ p {\displaystyle p\to \Box \Diamond p} . In fact, to do so is to commit the naturalistic fallacy (i.e. to state that what is natural is also good, by saying that if p is the case, p ought to be permitted).