43 ideas
7798 | There are three axiom schemas for propositional logic [Girle] |
7786 | Propositional logic handles negation, disjunction, conjunction; predicate logic adds quantifiers, predicates, relations [Girle] |
7799 | Proposition logic has definitions for its three operators: or, and, and identical [Girle] |
7797 | Axiom systems of logic contain axioms, inference rules, and definitions of proof and theorems [Girle] |
14684 | A world is 'accessible' to another iff the first is possible according to the second [Salmon,N] |
14669 | For metaphysics, T may be the only correct system of modal logic [Salmon,N] |
14667 | System B has not been justified as fallacy-free for reasoning on what might have been [Salmon,N] |
14668 | In B it seems logically possible to have both p true and p is necessarily possibly false [Salmon,N] |
14692 | System B implies that possibly-being-realized is an essential property of the world [Salmon,N] |
14671 | What is necessary is not always necessarily necessary, so S4 is fallacious [Salmon,N] |
7794 | There are seven modalities in S4, each with its negation [Girle] |
14686 | S5 modal logic ignores accessibility altogether [Salmon,N] |
7793 | ◊p → □◊p is the hallmark of S5 [Girle] |
14691 | S5 believers say that-things-might-have-been-that-way is essential to ways things might have been [Salmon,N] |
14693 | The unsatisfactory counterpart-theory allows the retention of S5 [Salmon,N] |
7795 | S5 has just six modalities, and all strings can be reduced to those [Girle] |
7787 | Possible worlds logics use true-in-a-world rather than true [Girle] |
7796 | Modal logics were studied in terms of axioms, but now possible worlds semantics is added [Girle] |
14670 | Metaphysical (alethic) modal logic concerns simple necessity and possibility (not physical, epistemic..) [Salmon,N] |
7788 | Modal logic has four basic modal negation equivalences [Girle] |
7789 | Necessary implication is called 'strict implication'; if successful, it is called 'entailment' [Girle] |
7790 | If an argument is invalid, a truth tree will indicate a counter-example [Girle] |
13191 | The properties of a thing flow from its essence [Leibniz] |
14678 | Any property is attached to anything in some possible world, so I am a radical anti-essentialist [Salmon,N] |
14680 | Logical possibility contains metaphysical possibility, which contains nomological possibility [Salmon,N] |
7800 | Analytic truths are divided into logically and conceptually necessary [Girle] |
14690 | In the S5 account, nested modalities may be unseen, but they are still there [Salmon,N] |
14677 | Metaphysical necessity is said to be unrestricted necessity, true in every world whatsoever [Salmon,N] |
14679 | Bizarre identities are logically but not metaphysically possible, so metaphysical modality is restricted [Salmon,N] |
14688 | Without impossible worlds, the unrestricted modality that is metaphysical has S5 logic [Salmon,N] |
14685 | Metaphysical necessity is NOT truth in all (unrestricted) worlds; necessity comes first, and is restricted [Salmon,N] |
14681 | Logical necessity is free of constraints, and may accommodate all of S5 logic [Salmon,N] |
14676 | Nomological necessity is expressed with intransitive relations in modal semantics [Salmon,N] |
7801 | Possibilities can be logical, theoretical, physical, economic or human [Girle] |
14689 | Necessity and possibility are not just necessity and possibility according to the actual world [Salmon,N] |
7792 | A world has 'access' to a world it generates, which is important in possible worlds semantics [Girle] |
14674 | Impossible worlds are also ways for things to be [Salmon,N] |
14682 | Denial of impossible worlds involves two different confusions [Salmon,N] |
14687 | Without impossible worlds, how things might have been is the only way for things to be [Salmon,N] |
14683 | Possible worlds rely on what might have been, so they can' be used to define or analyse modality [Salmon,N] |
14672 | Possible worlds are maximal abstract ways that things might have been [Salmon,N] |
14675 | Possible worlds just have to be 'maximal', but they don't have to be consistent [Salmon,N] |
14673 | You can't define worlds as sets of propositions, and then define propositions using worlds [Salmon,N] |