|Modal logic: the modal logic is an extension of classical logic to systems in which possibility and necessity can also be expressed. Different approaches use operators to express "necessary" and "possible", which, depending on the placement within formulas, can let claims of different strengths win. E.g. there is an object which necessarily has the property F/it is necessary that there is an object with the property F. The introduction of possible worlds makes quantification possible for expressing possibility (There is at least one world in which ...) and necessity (For all worlds is valid ...). See also operators, quantifier, completion, range, possible worlds.|
Books on Amazon
Alethic modal logic/Hintikka: the alethic modal logic cannot be an axiomatized logical system and does not allow deductive treatment of the quantified logic of the logical modalities.
Logical modalities/logical necessity/logical possibility/Hintikka: neither Kripke's nor Lewis' system allows modal logic for logical modalities.
Kripke/Hintikka: this also shows that the step from its logic to the standard logic is a very far step.
Jaakko and Merrill B. Hintikka
The Logic of Epistemology and the Epistemology of Logic Dordrecht 1989
J. Hintikka/M. B. Hintikka
Untersuchungen zu Wittgenstein Frankfurt 1996