84 ideas
| 4588 | There is no such thing as 'science'; there are just many different sciences [Heil] |
| 13689 | 'Theorems' are formulas provable from no premises at all [Sider] |
| 13705 | Truth tables assume truth functionality, and are just pictures of truth functions [Sider] |
| 13706 | Intuitively, deontic accessibility seems not to be reflexive, but to be serial [Sider] |
| 13710 | In D we add that 'what is necessary is possible'; then tautologies are possible, and contradictions not necessary [Sider] |
| 13711 | System B introduces iterated modalities [Sider] |
| 13708 | S5 is the strongest system, since it has the most valid formulas, because it is easy to be S5-valid [Sider] |
| 13712 | Epistemic accessibility is reflexive, and allows positive and negative introspection (KK and K¬K) [Sider] |
| 13714 | We can treat modal worlds as different times [Sider] |
| 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] |
| 13715 | You can employ intuitionist logic without intuitionism about mathematics [Sider] |
| 13678 | The most popular account of logical consequence is the semantic or model-theoretic one [Sider] |
| 13679 | Maybe logical consequence is more a matter of provability than of truth-preservation [Sider] |
| 13682 | Maybe logical consequence is impossibility of the premises being true and the consequent false [Sider] |
| 13680 | Maybe logical consequence is a primitive notion [Sider] |
| 13722 | A 'theorem' is an axiom, or the last line of a legitimate proof [Sider] |
| 13696 | When a variable is 'free' of the quantifier, the result seems incapable of truth or falsity [Sider] |
| 13700 | A 'total' function must always produce an output for a given domain [Sider] |
| 13703 | λ can treat 'is cold and hungry' as a single predicate [Sider] |
| 13688 | Good axioms should be indisputable logical truths [Sider] |
| 13687 | No assumptions in axiomatic proofs, so no conditional proof or reductio [Sider] |
| 13690 | Proof by induction 'on the length of the formula' deconstructs a formula into its accepted atoms [Sider] |
| 13691 | Induction has a 'base case', then an 'inductive hypothesis', and then the 'inductive step' [Sider] |
| 13685 | Natural deduction helpfully allows reasoning with assumptions [Sider] |
| 13686 | We can build proofs just from conclusions, rather than from plain formulae [Sider] |
| 13697 | Valuations in PC assign truth values to formulas relative to variable assignments [Sider] |
| 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] |
| 13724 | In model theory, first define truth, then validity as truth in all models, and consequence as truth-preservation [Sider] |
| 13698 | In a complete logic you can avoid axiomatic proofs, by using models to show consequences [Sider] |
| 13699 | Compactness surprisingly says that no contradictions can emerge when the set goes infinite [Sider] |
| 13701 | A single second-order sentence validates all of arithmetic - but this can't be proved axiomatically [Sider] |
| 4616 | A higher level is 'supervenient' if it is determined by lower levels, but has its own natural laws [Heil] |
| 13692 | A 'precisification' of a trivalent interpretation reduces it to a bivalent interpretation [Sider] |
| 13695 | Supervaluational logic is classical, except when it adds the 'Definitely' operator [Sider] |
| 13693 | A 'supervaluation' assigns further Ts and Fs, if they have been assigned in every precisification [Sider] |
| 13694 | We can 'sharpen' vague terms, and then define truth as true-on-all-sharpenings [Sider] |
| 13683 | A relation is a feature of multiple objects taken together [Sider] |
| 4603 | Functionalists in Fodor's camp usually say that a genuine property is one that figures in some causal laws [Heil] |
| 4617 | A stone does not possess the property of being a stone; its other properties make it a stone [Heil] |
| 4615 | Complex properties are not new properties, they are merely new combinations of properties [Heil] |
| 4612 | Complex properties are just arrangements of simple properties; they do not "emerge" as separate [Heil] |
| 4587 | From the property predicates P and Q, we can get 'P or Q', but it doesn't have to designate another property [Heil] |
| 4611 | The supporters of 'tropes' treat objects as bundles of tropes, when I think objects 'possess' properties [Heil] |
| 4592 | If you can have the boat without its current planks, and the planks with no boat, the planks aren't the boat [Heil] |
| 13702 | The identity of indiscernibles is necessarily true, if being a member of some set counts as a property [Sider] |
| 13721 | 'Strong' necessity in all possible worlds; 'weak' necessity in the worlds where the relevant objects exist [Sider] |
| 13707 | Maybe metaphysical accessibility is intransitive, if a world in which I am a frog is impossible [Sider] |
| 13709 | Logical truths must be necessary if anything is [Sider] |
| 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] |
| 4586 | You can't embrace the formal apparatus of possible worlds, but reject the ontology [Heil] |
| 13717 | Transworld identity is not a problem in de dicto sentences, which needn't identify an individual [Sider] |
| 13719 | Barcan Formula problem: there might have been a ghost, despite nothing existing which could be a ghost [Sider] |
| 4591 | Idealism explains appearances by identifying appearances with reality [Heil] |
| 4610 | Different generations focus on either the quality of mind, or its scientific standing, or the content of thought [Heil] |
| 4618 | If minds are realised materially, it looks as if the material laws will pre-empt any causal role for mind [Heil] |
| 4621 | Whatever exists has qualities, so it is no surprise that states of minds have qualities [Heil] |
| 4623 | Propositional attitudes are not the only intentional states; there is also mental imagery [Heil] |
| 4626 | The widespread externalist view says intentionality has content because of causal links of agent to world [Heil] |
| 4622 | Error must be possible in introspection, because error is possible in all judgements [Heil] |
| 4590 | If causation is just regularities in events, the interaction of mind and body is not a special problem [Heil] |
| 4614 | Disposition is a fundamental feature of reality, since basic particles are capable of endless possible interactions [Heil] |
| 4595 | No mental state entails inevitable behaviour, because other beliefs or desires may intervene [Heil] |
| 4599 | Hearts are material, but functionalism says the property of being a heart is not a material property [Heil] |
| 4624 | If you are a functionalist, there appears to be no room for qualia [Heil] |
| 4601 | Higher-level sciences cannot be reduced, because their concepts mark boundaries invisible at lower levels [Heil] |
| 4602 | Higher-level sciences designate real properties of objects, which are not reducible to lower levels [Heil] |
| 4593 | 'Property dualism' says mind and body are not substances, but distinct families of properties [Heil] |
| 4597 | Early identity theory talked of mind and brain 'processes', but now the focus is properties [Heil] |
| 4609 | It seems contradictory to be asked to believe that we can be eliminativist about beliefs [Heil] |
| 4596 | The appeal of the identity theory is its simplicity, and its solution to the mental causation problem [Heil] |
| 4598 | Functionalists emphasise that mental processes are not to be reduced to what realises them [Heil] |
| 4619 | 'Multiple realisability' needs to clearly distinguish low-level realisers from what is realised [Heil] |
| 4620 | Multiple realisability is not a relation among properties, but an application of predicates to resembling things [Heil] |
| 4594 | A scientist could know everything about the physiology of headaches, but never have had one [Heil] |
| 4625 | Is mental imagery pictorial, or is it propositional? [Heil] |
| 4607 | Folk psychology and neuroscience are no more competitors than cartography and geology are [Heil] |
| 4605 | Truth-conditions correspond to the idea of 'literal meaning' [Heil] |
| 4606 | To understand 'birds warble' and 'tigers growl', you must also understand 'tigers warble' [Heil] |
| 4604 | If propositions are abstract entities, how do human beings interact with them? [Heil] |
| 13304 | Learned men gain more in one day than others do in a lifetime [Posidonius] |
| 20820 | Time is an interval of motion, or the measure of speed [Posidonius, by Stobaeus] |