- FDE with K ModalSemantics
A
frame comprises the interpretation of sentences and predicates at a world. A model comprises a non-empty collection of frames, a world access relation , and a set of constants (the domain).The semantics for predication, quantification, and truth-functional operators are the same as .
Modal Operators
Possibility
The value of a necessity sentence ◻A at is the maximum value of its operand at each world such that is in .
Necessity
The value of a necessity sentence ◻A at is the minimum value of its operand at each world such that is in .
Consequence
Logical Consequence is defined similary as , except with reference to a world:
Logical Consequence
C is a Logical Consequence of A iff all models where A has a desginated value at
are models where C also has a designated value at .Tableaux
Nodes
Nodes for many-valued modal tableaux come in two types:
A node consisting of a sentence, a designation marker (⊕ or ⊖), and a world.
An access node like
, indicating that the pair is in the access relation .
Trunk
To build the trunk for an argument, add a designated node with each premise at world
, followed by an undesignated node with the the conclusion at world .Closure
Rules
Non-modal rules for counterparts, with the addition of carrying over the world marker from the target node(s).
are exactly like theirModal Operator Rules
◇ Rules
◻ Rules
Operator Rules
¬ Rules
∧ Rules
∨ Rules
⊃ Rules
≡ Rules
- ≡⊖Material Biconditional Undesignated[source]
- A ≡ B ⊖, w0⋮A ⊖, w0¬B ⊖, w0¬A ⊖, w0B ⊖, w0
Quantifier Rules
∃ Rules
∀ Rules
Compatibility Rules
⚬ Rules
→ Rules
↔ Rules
- ↔⊖Biconditional Undesignated[source]
- A ↔ B ⊖, w0⋮A ⊖, w0¬B ⊖, w0¬A ⊖, w0B ⊖, w0
Notes
Like
, there are no logical truths.The standard modal operator interdefinabilities hold: ◻A ⟛ ¬◇¬A and ¬◻A ⟛ ◇¬A.
Modal forms of modus ponens fail, e.g. ◻(A → B), ◇A ⊬ ◇B.
References
Priest, Graham. An Introduction to Non-Classical Logic: From If to Is. Cambridge University Press, 2008.