|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._____________Annotation: The above characterizations of concepts are neither definitions nor exhausting presentations of problems related to them. Instead, they are intended to give a short introduction to the contributions below. – Lexicon of Arguments.|
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Modal logic/Lewis: can be replaced by non-modal reasoning about possible objects - with non-modal arguments we have clear validity conditions.
Modal logic/tradition/Lewis: the traditional modal logic knows no accessibility relation - i.e. all possible worlds are always accessible from everywhere._____________Explanation of symbols: Roman numerals indicate the source, arabic numerals indicate the page number. The corresponding books are indicated on the right hand side. ((s)…): Comment by the sender of the contribution.
Die Identität von Körper und Geist Frankfurt 1989
Konventionen Berlin 1975
Philosophical Papers Bd I New York Oxford 1983
Philosophical Papers Bd II New York Oxford 1986
Cl. I. Lewis
Mind and the World Order: Outline of a Theory of Knowledge (Dover Books on Western Philosophy) 1991