16 ideas
| 13838 | A decent modern definition should always imply a semantics [Hacking] |
| Full Idea: Today we expect that anything worth calling a definition should imply a semantics. | |
| From: Ian Hacking (What is Logic? [1979], §10) | |
| A reaction: He compares this with Gentzen 1935, who was attempting purely syntactic definitions of the logical connectives. |
| 13833 | 'Thinning' ('dilution') is the key difference between deduction (which allows it) and induction [Hacking] |
| Full Idea: 'Dilution' (or 'Thinning') provides an essential contrast between deductive and inductive reasoning; for the introduction of new premises may spoil an inductive inference. | |
| From: Ian Hacking (What is Logic? [1979], §06.2) | |
| A reaction: That is, inductive logic (if there is such a thing) is clearly non-monotonic, whereas classical inductive logic is monotonic. |
| 13834 | Gentzen's Cut Rule (or transitivity of deduction) is 'If A |- B and B |- C, then A |- C' [Hacking] |
| Full Idea: If A |- B and B |- C, then A |- C. This generalises to: If Γ|-A,Θ and Γ,A |- Θ, then Γ |- Θ. Gentzen called this 'cut'. It is the transitivity of a deduction. | |
| From: Ian Hacking (What is Logic? [1979], §06.3) | |
| A reaction: I read the generalisation as 'If A can be either a premise or a conclusion, you can bypass it'. The first version is just transitivity (which by-passes the middle step). |
| 13835 | Only Cut reduces complexity, so logic is constructive without it, and it can be dispensed with [Hacking] |
| Full Idea: Only the cut rule can have a conclusion that is less complex than its premises. Hence when cut is not used, a derivation is quite literally constructive, building up from components. Any theorem obtained by cut can be obtained without it. | |
| From: Ian Hacking (What is Logic? [1979], §08) |
| 13845 | The various logics are abstractions made from terms like 'if...then' in English [Hacking] |
| Full Idea: I don't believe English is by nature classical or intuitionistic etc. These are abstractions made by logicians. Logicians attend to numerous different objects that might be served by 'If...then', like material conditional, strict or relevant implication. | |
| From: Ian Hacking (What is Logic? [1979], §15) | |
| A reaction: The idea that they are 'abstractions' is close to my heart. Abstractions from what? Surely 'if...then' has a standard character when employed in normal conversation? |
| 13840 | First-order logic is the strongest complete compact theory with Löwenheim-Skolem [Hacking] |
| Full Idea: First-order logic is the strongest complete compact theory with a Löwenheim-Skolem theorem. | |
| From: Ian Hacking (What is Logic? [1979], §13) |
| 13844 | A limitation of first-order logic is that it cannot handle branching quantifiers [Hacking] |
| Full Idea: Henkin proved that there is no first-order treatment of branching quantifiers, which do not seem to involve any idea that is fundamentally different from ordinary quantification. | |
| From: Ian Hacking (What is Logic? [1979], §13) | |
| A reaction: See Hacking for an example of branching quantifiers. Hacking is impressed by this as a real limitation of the first-order logic which he generally favours. |
| 10594 | Henkin semantics is more plausible for plural logic than for second-order logic [Maddy] |
| Full Idea: Henkin-style semantics seem to me more plausible for plural logic than for second-order logic. | |
| From: Penelope Maddy (Second Philosophy [2007], III.8 n1) | |
| A reaction: Henkin-style semantics are presented by Shapiro as the standard semantics for second-order logic. |
| 13842 | Second-order completeness seems to need intensional entities and possible worlds [Hacking] |
| Full Idea: Second-order logic has no chance of a completeness theorem unless one ventures into intensional entities and possible worlds. | |
| From: Ian Hacking (What is Logic? [1979], §13) |
| 13837 | With a pure notion of truth and consequence, the meanings of connectives are fixed syntactically [Hacking] |
| Full Idea: My doctrine is that the peculiarity of the logical constants resides precisely in that given a certain pure notion of truth and consequence, all the desirable semantic properties of the constants are determined by their syntactic properties. | |
| From: Ian Hacking (What is Logic? [1979], §09) | |
| A reaction: He opposes this to Peacocke 1976, who claims that the logical connectives are essentially semantic in character, concerned with the preservation of truth. |
| 13839 | Perhaps variables could be dispensed with, by arrows joining places in the scope of quantifiers [Hacking] |
| Full Idea: For some purposes the variables of first-order logic can be regarded as prepositions and place-holders that could in principle be dispensed with, say by a system of arrows indicating what places fall in the scope of which quantifier. | |
| From: Ian Hacking (What is Logic? [1979], §11) | |
| A reaction: I tend to think of variables as either pronouns, or as definite descriptions, or as temporary names, but not as prepositions. Must address this new idea... |
| 13843 | If it is a logic, the Löwenheim-Skolem theorem holds for it [Hacking] |
| Full Idea: A Löwenheim-Skolem theorem holds for anything which, on my delineation, is a logic. | |
| From: Ian Hacking (What is Logic? [1979], §13) | |
| A reaction: I take this to be an unusually conservative view. Shapiro is the chap who can give you an alternative view of these things, or Boolos. |
| 20440 | Art is a referential activity, hence indefinable, but it has a set of symptoms [Goodman] |
| Full Idea: No definition of art is possible (since it is a referential activity), …but the symptoms of art are syntactic density, semantic density, syntactic repleteness, exemplificationality, and multiple and complex reference. | |
| From: Nelson Goodman (Languages of Art (2nd edn) [1968], p.22-255), quoted by Alessandro Giovannelli - Nelson Goodman (aesthetics) 4 | |
| A reaction: I wish these labels were more self-explanatory. Goodman seems to want to assimilate art to his earlier interests in linguistic anti-realism and mereology. I wouldn't have thought he now had many followers. |
| 20439 | Artistic symbols are judged by the fruitfulness of their classifications [Goodman, by Giovannelli] |
| Full Idea: Artistic symbols are to be judged for the classifications they bring about, for how novel and insightful those classifications are, for how they change our world perceptions and relations. | |
| From: report of Nelson Goodman (Languages of Art (2nd edn) [1968]) by Alessandro Giovannelli - Nelson Goodman (aesthetics) 4 | |
| A reaction: This seems to be an awfully long way from our normal experience of art. I understand 'symbols' in early Flemish art, but not in Mondriaan, or even Rembrandt. |
| 20438 | A performance is only an instance of a work if there is not a single error [Goodman] |
| Full Idea: The most miserable performance without actual mistakes does count as an instance of a work, …but the most brilliant performance with a single wrong note does not. | |
| From: Nelson Goodman (Languages of Art (2nd edn) [1968], p.186), quoted by Alessandro Giovannelli - Nelson Goodman (aesthetics) | |
| A reaction: Mereological essentialism applied to art! You need to be a highly theoretical and technical philosopher (which Goodman was) to maintain such a weird and contrary-usage proposal. |
| 20437 | A copy only becomes an 'instance' of an artwork if there is a system of notation [Goodman] |
| Full Idea: Paintings and sculptures do not work within a notation; hence, there is no copying of an original that would preserve its originality. A copy of a painting is a copy, not an instance of the original. | |
| From: Nelson Goodman (Languages of Art (2nd edn) [1968], p.212), quoted by Alessandro Giovannelli - Nelson Goodman (aesthetics) 2 | |
| A reaction: Sounds conclusive, but isn't. Is a poetry manuscript a 'notation' or an original? Why is an etching plate a notation, but painting on canvas is an original? Can I create a painting specifically so that it can be copied (by my students)? Intention matters. |