11 ideas
| 10688 | 'Equivocation' is when terms do not mean the same thing in premises and conclusion [Beall/Restall] |
| Full Idea: 'Equivocation' is when the terms do not mean the same thing in the premises and in the conclusion. | |
| From: JC Beall / G Restall (Logical Consequence [2005], Intro) |
| 10690 | Formal logic is invariant under permutations, or devoid of content, or gives the norms for thought [Beall/Restall] |
| Full Idea: Logic is purely formal either when it is invariant under permutation of object (Tarski), or when it has totally abstracted away from all contents, or it is the constitutive norms for thought. | |
| From: JC Beall / G Restall (Logical Consequence [2005], 2) | |
| A reaction: [compressed] The third account sounds rather woolly, and the second one sounds like a tricky operation, but the first one sounds clear and decisive, so I vote for Tarski. |
| 10691 | Logical consequence needs either proofs, or absence of counterexamples [Beall/Restall] |
| Full Idea: Technical work on logical consequence has either focused on proofs, where validity is the existence of a proof of the conclusions from the premises, or on models, which focus on the absence of counterexamples. | |
| From: JC Beall / G Restall (Logical Consequence [2005], 3) |
| 10695 | Logical consequence is either necessary truth preservation, or preservation based on interpretation [Beall/Restall] |
| Full Idea: Two different views of logical consequence are necessary truth-preservation (based on modelling possible worlds; favoured by Realists), or truth-preservation based on the meanings of the logical vocabulary (differing in various models; for Anti-Realists). | |
| From: JC Beall / G Restall (Logical Consequence [2005], 2) | |
| A reaction: Thus Dummett prefers the second view, because the law of excluded middle is optional. My instincts are with the first one. |
| 10689 | A step is a 'material consequence' if we need contents as well as form [Beall/Restall] |
| Full Idea: A logical step is a 'material consequence' and not a formal one, if we need the contents as well as the structure or form. | |
| From: JC Beall / G Restall (Logical Consequence [2005], 2) |
| 10696 | A 'logical truth' (or 'tautology', or 'theorem') follows from empty premises [Beall/Restall] |
| Full Idea: If a conclusion follows from an empty collection of premises, it is true by logic alone, and is a 'logical truth' (sometimes a 'tautology'), or, in the proof-centred approach, 'theorems'. | |
| From: JC Beall / G Restall (Logical Consequence [2005], 4) | |
| A reaction: These truths are written as following from the empty set Φ. They are just implications derived from the axioms and the rules. |
| 10693 | Models are mathematical structures which interpret the non-logical primitives [Beall/Restall] |
| Full Idea: Models are abstract mathematical structures that provide possible interpretations for each of the non-logical primitives in a formal language. | |
| From: JC Beall / G Restall (Logical Consequence [2005], 3) |
| 10692 | Hilbert proofs have simple rules and complex axioms, and natural deduction is the opposite [Beall/Restall] |
| Full Idea: There are many proof-systems, the main being Hilbert proofs (with simple rules and complex axioms), or natural deduction systems (with few axioms and many rules, and the rules constitute the meaning of the connectives). | |
| From: JC Beall / G Restall (Logical Consequence [2005], 3) |
| 10650 | In the military, persons are parts of parts of large units, but not parts of those large units [Rescher] |
| Full Idea: In military usage, persons can be parts of small units, and small units parts of large ones; but persons are never parts of large units. | |
| From: Nicholas Rescher (Axioms for the Part Relation [1955]), quoted by Achille Varzi - Mereology 2.1 | |
| A reaction: This much-cited objection to the transitivity of the 'part' relation seems very odd. There could hardly be an army or a regiment if there weren't soldiers to make up parts of it. |
| 12719 | Clearly, force is that from which action follows, when unimpeded [Leibniz] |
| Full Idea: The notion of force is as clear as that of action and passion, because it is that from which action follows when nothing prevents it. | |
| From: Gottfried Leibniz (Letters to Paul Pellison-Fontinier [1691], A1.6.226), quoted by Daniel Garber - Leibniz:Body,Substance,Monad 4 | |
| A reaction: For Leibniz, force seems to be a metaphysical notion, rather than a feature of the physical world. I take it to be the bottom level of explanation, and it equates with Aristotelian form and essence. |
| 12720 | Time doesn't exist, since its parts don't coexist [Leibniz] |
| Full Idea: Time never exists, since all of its parts never exist together. | |
| From: Gottfried Leibniz (Letters to Paul Pellison-Fontinier [1691], A1.6.226), quoted by Daniel Garber - Leibniz:Body,Substance,Monad 4 | |
| A reaction: The problem here is that he seems to be admitting that time has 'parts'. Can something have parts and not exist? Events will also fail to exist by this criterion, though we could hardly deny that events (or some such) 'happen'. |