17 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. |
| 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. |
| 14534 | Shoemaker moved from properties as powers to properties bestowing powers [Shoemaker, by Mumford/Anjum] |
| Full Idea: Shoemaker ventured the theory in 1980 that properties just are clusters of powers, but he has subsequently abandoned this, and now thinks properties bestow their bearers with causal powers. | |
| From: report of Sydney Shoemaker (Self, Body and Coincidence [1999], p.297) by S.Mumford/R.Lill Anjum - Getting Causes from Powers 1.1 | |
| A reaction: Like Mumford and Anjum, I prefer the earlier theory. I think taking powers as basic is the only story that really makes sense. A power is intrinsic and primitive, whereas properties are complex, messy, partly subjective, and higher level. |
| 9758 | To make sense of personal identity, focus on agency rather than experience [Korsgaard] |
| Full Idea: A focus on agency makes more sense of personal identity than a focus on experience. | |
| From: Christine M. Korsgaard (Intro to 'Creating the Kingdom of Ends' [1996], §2) | |
| A reaction: This strikes me as eminently sensible advice for the beginning of any discussion of personal identity. Her personal bête noir is Parfit, who focuses on what we are conscious of. |
| 9757 | A person viewed as an agent makes no sense without its own future [Korsgaard] |
| Full Idea: In forming a particular plan of life, you need to identify with your future in order to be what you are even now. When the person is viewed as an agent, no clear content can be given to the idea of a merely present self. | |
| From: Christine M. Korsgaard (Intro to 'Creating the Kingdom of Ends' [1996], §2) | |
| A reaction: I certainly like the notion that we should treat persons primarily as agents, since I take personhood to be more like a process than an existent entity. If a large brick is about to hit you, you actually have no future, though you think you have. |
| 9759 | Theory of action focuses on explanation and prediction; practical action on justification and choice [Korsgaard] |
| Full Idea: When we look at our actions from the theoretical standpoint our concern is with their explanation and prediction. When we view them from the practical standpoint our concern is with their justification and choice. | |
| From: Christine M. Korsgaard (Intro to 'Creating the Kingdom of Ends' [1996], §4) | |
| A reaction: A nice distinction, which invites us to further subdivide action theory into two branches, with entirely different concerns. |
| 9760 | Self-concern may be a source of pain, or a lack of self-respect, or a failure of responsibility [Korsgaard] |
| Full Idea: For utilitarians, self-concern causes needless pain; for Kantians, it evinces a lack of respect for one's own humanity; for the religious moralist, it is a failure of responsibility for what has been placed in one's special care. | |
| From: Christine M. Korsgaard (Intro to 'Creating the Kingdom of Ends' [1996], §5) | |
| A reaction: Worryingly, given my heathenish views, I find the third one the most congenial. If we don't take responsibility for our own selves (e.g. for having a great talent), then no one (even parents) will take responsibility for anything. |
| 9761 | Personal concern for one's own self widens out into concern for the impersonal [Korsgaard] |
| Full Idea: The personal concern which begins with one's life in a particular body finds its place in ever-widening spheres of agency and enterprise, developing finally into a personal concern for the impersonal. | |
| From: Christine M. Korsgaard (Intro to 'Creating the Kingdom of Ends' [1996], §5) | |
| A reaction: I am very struck by this nice thought, which comes from a very committed Kantian. It seems to me to capture the modern orthodoxy in ethical thinking - that concern for one's self, rather than altruism, is central, but altruism should follow from it. |