Combining Texts

All the ideas for 'Possible Worlds', 'The Question of Realism' and 'Logic for Philosophy'

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63 ideas

1. Philosophy / E. Nature of Metaphysics / 2. Possibility of Metaphysics
15053 If metaphysics can't be settled, it hardly matters whether it makes sense [Fine,K]
1. Philosophy / E. Nature of Metaphysics / 7. Against Metaphysics
15054 'Quietist' says abandon metaphysics because answers are unattainable (as in Kant's noumenon) [Fine,K]
4. Formal Logic / B. Propositional Logic PL / 2. Tools of Propositional Logic / b. Terminology of PL
13689 'Theorems' are formulas provable from no premises at all [Sider]
4. Formal Logic / B. Propositional Logic PL / 3. Truth Tables
13705 Truth tables assume truth functionality, and are just pictures of truth functions [Sider]
4. Formal Logic / D. Modal Logic ML / 3. Modal Logic Systems / c. System D
13710 In D we add that 'what is necessary is possible'; then tautologies are possible, and contradictions not necessary [Sider]
13706 Intuitively, deontic accessibility seems not to be reflexive, but to be serial [Sider]
4. Formal Logic / D. Modal Logic ML / 3. Modal Logic Systems / f. System B
13711 System B introduces iterated modalities [Sider]
4. Formal Logic / D. Modal Logic ML / 3. Modal Logic Systems / h. System S5
13708 S5 is the strongest system, since it has the most valid formulas, because it is easy to be S5-valid [Sider]
4. Formal Logic / D. Modal Logic ML / 5. Epistemic Logic
13712 Epistemic accessibility is reflexive, and allows positive and negative introspection (KK and K¬K) [Sider]
4. Formal Logic / D. Modal Logic ML / 6. Temporal Logic
13714 We can treat modal worlds as different times [Sider]
4. Formal Logic / D. Modal Logic ML / 7. Barcan Formula
13720 Converse Barcan Formula: □∀αφ→∀α□φ [Sider]
13718 The Barcan Formula ∀x□Fx→□∀xFx may be a defect in modal logic [Sider]
13723 System B is needed to prove the Barcan Formula [Sider]
4. Formal Logic / E. Nonclassical Logics / 2. Intuitionist Logic
13715 You can employ intuitionist logic without intuitionism about mathematics [Sider]
5. Theory of Logic / B. Logical Consequence / 1. Logical Consequence
13680 Maybe logical consequence is a primitive notion [Sider]
13679 Maybe logical consequence is more a matter of provability than of truth-preservation [Sider]
13678 The most popular account of logical consequence is the semantic or model-theoretic one [Sider]
13682 Maybe logical consequence is impossibility of the premises being true and the consequent false [Sider]
5. Theory of Logic / B. Logical Consequence / 3. Deductive Consequence |-
13722 A 'theorem' is an axiom, or the last line of a legitimate proof [Sider]
5. Theory of Logic / E. Structures of Logic / 4. Variables in Logic
13696 When a variable is 'free' of the quantifier, the result seems incapable of truth or falsity [Sider]
5. Theory of Logic / E. Structures of Logic / 5. Functions in Logic
13700 A 'total' function must always produce an output for a given domain [Sider]
5. Theory of Logic / F. Referring in Logic / 3. Property (λ-) Abstraction
13703 λ can treat 'is cold and hungry' as a single predicate [Sider]
5. Theory of Logic / H. Proof Systems / 2. Axiomatic Proof
13687 No assumptions in axiomatic proofs, so no conditional proof or reductio [Sider]
13688 Good axioms should be indisputable logical truths [Sider]
5. Theory of Logic / H. Proof Systems / 3. Proof from Assumptions
13691 Induction has a 'base case', then an 'inductive hypothesis', and then the 'inductive step' [Sider]
13690 Proof by induction 'on the length of the formula' deconstructs a formula into its accepted atoms [Sider]
5. Theory of Logic / H. Proof Systems / 4. Natural Deduction
13685 Natural deduction helpfully allows reasoning with assumptions [Sider]
5. Theory of Logic / H. Proof Systems / 6. Sequent Calculi
13686 We can build proofs just from conclusions, rather than from plain formulae [Sider]
5. Theory of Logic / I. Semantics of Logic / 1. Semantics of Logic
13697 Valuations in PC assign truth values to formulas relative to variable assignments [Sider]
5. Theory of Logic / I. Semantics of Logic / 3. Logical Truth
13684 The semantical notion of a logical truth is validity, being true in all interpretations [Sider]
13704 It is hard to say which are the logical truths in modal logic, especially for iterated modal operators [Sider]
5. Theory of Logic / J. Model Theory in Logic / 1. Logical Models
13724 In model theory, first define truth, then validity as truth in all models, and consequence as truth-preservation [Sider]
5. Theory of Logic / K. Features of Logics / 4. Completeness
13698 In a complete logic you can avoid axiomatic proofs, by using models to show consequences [Sider]
5. Theory of Logic / K. Features of Logics / 6. Compactness
13699 Compactness surprisingly says that no contradictions can emerge when the set goes infinite [Sider]
6. Mathematics / B. Foundations for Mathematics / 4. Axioms for Number / e. Peano arithmetic 2nd-order
13701 A single second-order sentence validates all of arithmetic - but this can't be proved axiomatically [Sider]
7. Existence / C. Structure of Existence / 1. Grounding / a. Nature of grounding
15007 If you make 'grounding' fundamental, you have to mention some non-fundamental notions [Sider on Fine,K]
15006 Something is grounded when it holds, and is explained, and necessitated by something else [Fine,K, by Sider]
7. Existence / C. Structure of Existence / 1. Grounding / b. Relata of grounding
15055 Grounding relations are best expressed as relations between sentences [Fine,K]
7. Existence / C. Structure of Existence / 2. Reduction
15050 Reduction might be producing a sentence which gets closer to the logical form [Fine,K]
15051 Reduction might be semantic, where a reduced sentence is understood through its reduction [Fine,K]
15052 Reduction is modal, if the reductions necessarily entail the truth of the target sentence [Fine,K]
15056 The notion of reduction (unlike that of 'ground') implies the unreality of what is reduced [Fine,K]
7. Existence / D. Theories of Reality / 3. Reality
15046 Reality is a primitive metaphysical concept, which cannot be understood in other terms [Fine,K]
15047 What is real can only be settled in terms of 'ground' [Fine,K]
15048 In metaphysics, reality is regarded as either 'factual', or as 'fundamental' [Fine,K]
15060 Why should what is explanatorily basic be therefore more real? [Fine,K]
7. Existence / D. Theories of Reality / 10. Vagueness / f. Supervaluation for vagueness
13692 A 'precisification' of a trivalent interpretation reduces it to a bivalent interpretation [Sider]
13693 A 'supervaluation' assigns further Ts and Fs, if they have been assigned in every precisification [Sider]
13695 Supervaluational logic is classical, except when it adds the 'Definitely' operator [Sider]
13694 We can 'sharpen' vague terms, and then define truth as true-on-all-sharpenings [Sider]
8. Modes of Existence / A. Relations / 1. Nature of Relations
13683 A relation is a feature of multiple objects taken together [Sider]
9. Objects / F. Identity among Objects / 7. Indiscernible Objects
13702 The identity of indiscernibles is necessarily true, if being a member of some set counts as a property [Sider]
10. Modality / A. Necessity / 3. Types of Necessity
13721 'Strong' necessity in all possible worlds; 'weak' necessity in the worlds where the relevant objects exist [Sider]
10. Modality / A. Necessity / 5. Metaphysical Necessity
13707 Maybe metaphysical accessibility is intransitive, if a world in which I am a frog is impossible [Sider]
10. Modality / A. Necessity / 6. Logical Necessity
13709 Logical truths must be necessary if anything is [Sider]
10. Modality / B. Possibility / 8. Conditionals / b. Types of conditional
13716 'If B hadn't shot L someone else would have' if false; 'If B didn't shoot L, someone else did' is true [Sider]
10. Modality / E. Possible worlds / 2. Nature of Possible Worlds / a. Nature of possible worlds
15793 We can take 'ways things might have been' as irreducible elements in our ontology [Stalnaker, by Lycan]
10. Modality / E. Possible worlds / 3. Transworld Objects / a. Transworld identity
13717 Transworld identity is not a problem in de dicto sentences, which needn't identify an individual [Sider]
10. Modality / E. Possible worlds / 3. Transworld Objects / e. Possible Objects
13719 Barcan Formula problem: there might have been a ghost, despite nothing existing which could be a ghost [Sider]
12. Knowledge Sources / B. Perception / 2. Qualities in Perception / d. Secondary qualities
15061 Although colour depends on us, we can describe the world that way if it picks out fundamentals [Fine,K]
14. Science / D. Explanation / 2. Types of Explanation / j. Explanations by reduction
15059 Grounding is an explanation of truth, and needs all the virtues of good explanations [Fine,K]
14. Science / D. Explanation / 3. Best Explanation / b. Ultimate explanation
15057 Ultimate explanations are in 'grounds', which account for other truths, which hold in virtue of the grounding [Fine,K]
19. Language / D. Propositions / 5. Unity of Propositions
15058 A proposition ingredient is 'essential' if changing it would change the truth-value [Fine,K]