23 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. |
| 7949 | Varied descriptions of an event will explain varied behaviour relating to it [Davidson, by Macdonald,C] |
| Full Idea: Davidson points out that we can only make sense of patterns of behaviour such as excuses if events can have more than one description. So I flip the light switch, turn on the light, illuminate the room, and alert a prowler, but I do only one thing. | |
| From: report of Donald Davidson (Action, Reasons and Causes [1963]) by Cynthia Macdonald - Varieties of Things Ch.5 | |
| A reaction: We can distinguish an event as an actual object, and as an intentional object. We can probably individuate intentional events quite well (according to our interests), but actual 'events' seem to flow into one another and overlap. |
| 16608 | Ockham was an anti-realist about the categories [William of Ockham, by Pasnau] |
| Full Idea: Ockham is the scholastic paradigm of anti-realism with respect to the categories. | |
| From: report of William of Ockham (Summula philosophiae naturalis [1320]) by Robert Pasnau - Metaphysical Themes 1274-1671 05.3 | |
| A reaction: These are the ten categories mentioned in Aristotle's book 'Categories'. |
| 16599 | Ockham says matter must be extended, so we don't need Quantity [William of Ockham, by Pasnau] |
| Full Idea: Ockham regards Quantity as an entirely superfluous ontological category, …because matter is intrinsically extended. | |
| From: report of William of Ockham (Summula philosophiae naturalis [1320]) by Robert Pasnau - Metaphysical Themes 1274-1671 04.4 |
| 16681 | Matter gets its quantity from condensation and rarefaction, which is just local motion [William of Ockham] |
| Full Idea: Matter is made to have a greater or lesser quantity not through its receiving any absolute accident, but through condensation and rarefaction alone. Parts come more or less close together, which can happen with local motion. | |
| From: William of Ockham (Summula philosophiae naturalis [1320], I.13), quoted by Robert Pasnau - Metaphysical Themes 1274-1671 15.1 | |
| A reaction: This is Ockham at his most modern, rejecting the odd idea of Quantity in favour of a modern corpuscular view of the mere motions of matter. |
| 20020 | If one action leads directly to another, they are all one action [Davidson, by Wilson/Schpall] |
| Full Idea: Davidson (1980 ess 1) agreed with Anscombe that if a person Fs by G-ing, then her act F = her act G. For example, if someone accidentally alerts a burglar, by deliberately turning on a light, by flipping a switch, these are all the same action. | |
| From: report of Donald Davidson (Action, Reasons and Causes [1963]) by Wilson,G/Schpall,S - Action 1.2 | |
| A reaction: I would have thought there was obviously a strong conventional element in individuating actions, depending on interest. An electrician is only interest in whether the light worked. The police are only interested in the disturbance of the burglar. |
| 20072 | We explain an intention by giving an account of acting with an intention [Davidson, by Stout,R] |
| Full Idea: The early Davidson championed the approach that we explain the idea of having an intention by providing an account of what it is to act with an intention. | |
| From: report of Donald Davidson (Action, Reasons and Causes [1963]) by Rowland Stout - Action 7 'Conclusion' | |
| A reaction: This eliminates the distinction between a prior intention, and the intention that maintains a process such as speech. It sounds almost behaviourist. |
| 20045 | Acting for a reason is a combination of a pro attitude, and a belief that the action is appropriate [Davidson] |
| Full Idea: Whenever someone does something for a reason he can be characterised as (a) having some sort of pro attitude towards action of a certain kind, and (b) believing (or knowing, perceiving, noticing, remembering) that his action is of that kind. | |
| From: Donald Davidson (Action, Reasons and Causes [1963], p.3-4), quoted by Rowland Stout - Action 3 'The belief-' | |
| A reaction: This is the earlier Davidson roughly endorsing the traditional belief-desire account of action. He is giving a reductive account of reasons. Deciding reasons were not reducible may have led him to property dualism. |
| 23734 | The best explanation of reasons as purposes for actions is that they are causal [Davidson, by Smith,M] |
| Full Idea: Davidson argues that the best interpretation of the teleological character of reason explanations is an intepretation in causal terms. | |
| From: report of Donald Davidson (Action, Reasons and Causes [1963]) by Michael Smith - The Moral Problem 4.4 | |
| A reaction: That is, this is the explanation of someone doing something 'because' they have this reason (rather than happening to have a reason). Smith observes that other mental states (such as beliefs) may also have this causal power. |
| 23737 | Reasons can give purposes to actions, without actually causing them [Smith,M on Davidson] |
| Full Idea: Only the Humean theory is able to make sense of reason explanation as a species of teleological explanation, and one may accept that reason explanations are teleological without accepting that they are causal. | |
| From: comment on Donald Davidson (Action, Reasons and Causes [1963]) by Michael Smith - The Moral Problem 4.6 | |
| A reaction: That is, reasons can give a purpose to an action, and thereby motivate it, without actually causing it. I agree with Smith. I certainly don't (usually, at least) experience reasons as directly producing my actions. Hume says desires are needed. |
| 20075 | Early Davidson says intentional action is caused by reasons [Davidson, by Stout,R] |
| Full Idea: In Davidson's earlier approach, intentional action requires causation by reasons. | |
| From: report of Donald Davidson (Action, Reasons and Causes [1963]) by Rowland Stout - Action 8 'Weakness' | |
| A reaction: A very Kantian idea, and one that seems to bestow causal powers on something which I take to be highly abstract. Thus Davidson was wrong (but in a nice way). |
| 6664 | Reasons must be causes when agents act 'for' reasons [Davidson, by Lowe] |
| Full Idea: It can be argued (by Davidson) that far from it being the case that reasons for and causes of action are quite distinct, reasons must be causes when agents act 'for' reasons. | |
| From: report of Donald Davidson (Action, Reasons and Causes [1963]) by E.J. Lowe - Introduction to the Philosophy of Mind Ch.9 | |
| A reaction: Lowe argues against this view. The rival views to Davidson would be either that reasons are no more than desires-plus-beliefs in disguise, or that the will causes actions, and strong reasons carry a great weight with the will. I like the will. |
| 3395 | Davidson claims that what causes an action is the reason for doing it [Davidson, by Kim] |
| Full Idea: Davidson defends the simple thesis that the reason for which an action is done is the one that causes it, …which means that agency is possible only if mental causation is possible. | |
| From: report of Donald Davidson (Action, Reasons and Causes [1963]) by Jaegwon Kim - Philosophy of Mind p.127 |