18 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. |
| 12302 | Definitions formed an abstract hierarchy for Aristotle, as sets do for us [Fine,K] |
| Full Idea: For us it is sets which constitute the most natural example of a hierarchical structure within the abstract realm; but for Aristotle it would have been definitions, via their natural division into genus and differentia. | |
| From: Kit Fine (Aristotle on Matter [1992], §1 n4) | |
| A reaction: I suppose everyone who thinks about reality in abstraction ends up with a hierarchy. Compare the hierarchy of angelic hosts, or Greek gods. Could we get back to the Aristotelian view, instead of sets, which are out of control at the top end? |
| 14266 | Aristotle sees hierarchies in definitions using genus and differentia (as we see them in sets) [Fine,K] |
| Full Idea: For us, sets constitute the most natural example of a hierarchical structure within the abstract realm. But for Aristotle it would have been definitions, via their natural division into genus and differentia. | |
| From: Kit Fine (Aristotle on Matter [1992], 1 n4) | |
| A reaction: Genus and differentia are only part of the story in Aristotle, and this remarks strikes me as perceptive. It is precisely the mapping of the explanatory hierarchy which Aristotle seeks in a good definition. |
| 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. |
| 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. |
| 14268 | Maybe bottom-up grounding shows constitution, and top-down grounding shows essence [Fine,K] |
| Full Idea: It may be that the two forms of grounding have a different source; the one from the bottom up is required for the constitution of the thing to be intelligible; the one from the top down is required for the essence of the thing to be intelligible. | |
| From: Kit Fine (Aristotle on Matter [1992], 2) | |
| A reaction: [He cites Aristotle Met. 1019a8-10 in support] Close reading of Fine would be needed to elucidate this properly, but it is a suggestive line of thought about how we should approach grounding. |
| 14267 | There is no distinctive idea of constitution, because you can't say constitution begins and ends [Fine,K] |
| Full Idea: If the parts of a body can constitute a man, then why should men not constitute a family? Why draw the line at the level of the man? ...Thus the idea of a distinctive notion of constitution, terminating in concrete substances, should be given up. | |
| From: Kit Fine (Aristotle on Matter [1992], 1) | |
| A reaction: This is in the context of Aristotle, but Fine's view seems to apply to Rudder Baker's distinctive approach. |
| 14264 | Is there a plausible Aristotelian notion of constitution, applicable to both physical and non-physical? [Fine,K] |
| Full Idea: There is a question of whether there is a viable conception of constitution of the sort Aristotle supposes, one which is uniformly applicable to physical and non-physical objects alike, and which is capable of hierarchical application. | |
| From: Kit Fine (Aristotle on Matter [1992], 1) | |
| A reaction: This is part of an explication of Aristotle's 'matter' [hule], which might be better translated as 'ingredients', which would fit non-physical things quite well. |
| 18265 | We don't judge by combining subject and concept; we get a concept by splitting up a judgement [Frege] |
| Full Idea: Instead of putting a judgement together out of an individual as subject and an already previously formed concept as predicate, we do the opposite and arrive at a concept by splitting up the content of possible judgement. | |
| From: Gottlob Frege (Boole calculus and the Concept script [1881], p.17) | |
| A reaction: This is behind holistic views of sentences, and hence of whole languages, and behind Quine's rejection of 'properties' inferred from the predicates in judgements. |
| 14265 | The components of abstract definitions could play the same role as matter for physical objects [Fine,K] |
| Full Idea: If one considers Aristotle's standard example of a definition, then it is plausible that its defining terms ('plane figure' in the case of a circle) should be constitutive of it in the same general way as physical matter constitutes something physical. | |
| From: Kit Fine (Aristotle on Matter [1992], 1) | |
| A reaction: It strikes me that an appropriate translation for the Greek 'hule' might be the English 'ingredients', since Fine seems to be right about the broad application of hule in Aristotle. |