20 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. |
| 5078 | Kant and Mill both try to explain right and wrong, without a divine lawgiver [Taylor,R] |
| Full Idea: Kant and Mill were in total agreement in trying to give content to the distinction between moral right and wrong, without recourse to any divine lawgiver. | |
| From: Richard Taylor (Virtue Ethics: an Introduction [2002], Ch.14) | |
| A reaction: A nice analysis, in tune with MacIntyre and others, who see such attempts as failures. It is hard, however, to deny the claims of rational principles, or of suffering, in our moral framework. I agree with Taylor's move back to virtue, but it ain't simple. |
| 5067 | Morality based on 'forbid', 'permit' and 'require' implies someone who does these things [Taylor,R] |
| Full Idea: If morality is based on wrong (meaning 'forbidden'), right ('permitted'), and obligatory ('required'), we are led to ask 'Who is it that thus permits, forbids or requires that certain things be done or not done?' | |
| From: Richard Taylor (Virtue Ethics: an Introduction [2002], Ch.2) | |
| A reaction: Clear reinforcement for Nietzsche's attack on conventional morals, which Taylor sees as a relic of medieval religious attitudes. Taylor says Kant offered a non-religious version of the same authority. I agree. Back to the Greek pursuit of excellence! |
| 5079 | Pleasure can have a location, and be momentary, and come and go - but happiness can't [Taylor,R] |
| Full Idea: Pleasures can be located in a particular part of the body, and can be momentary, and come and go, but this is not the case with happiness. | |
| From: Richard Taylor (Virtue Ethics: an Introduction [2002], Ch.16) | |
| A reaction: Probably no one ever thought that pleasure and happiness were actually identical - merely that pleasure is the only cause and source of happiness. These are good objections to that hypothesis. Pleasure simply isn't 'the good'. |
| 5068 | 'Eudaimonia' means 'having a good demon', implying supreme good fortune [Taylor,R] |
| Full Idea: The word 'eudaimonia' means literally 'having a good demon', which is apt, because it suggests some kind of supreme good fortune, of the sort which might be thought of as a bestowal. | |
| From: Richard Taylor (Virtue Ethics: an Introduction [2002], Ch.5) | |
| A reaction: Beware of etymology. This implies that eudaimonia is almost entirely beyond a person's control, but Aristotle doesn't think that. A combination of education and effort can build on some natural gifts to create a fully successful life. |
| 5076 | To Greeks it seemed obvious that the virtue of anything is the perfection of its function [Taylor,R] |
| Full Idea: To the Greeks it seemed obvious that the virtue of anything is the perfection of its function. | |
| From: Richard Taylor (Virtue Ethics: an Introduction [2002], Ch.10) | |
| A reaction: A problem case might be a work of art, but one might reply that there is no obvious perfection there because there is no clear function. For artefacts and organisms the principle seems very good. But 'Is the Cosmos good?' |
| 5077 | The modern idea of obligation seems to have lost the idea of an obligation 'to' something [Taylor,R] |
| Full Idea: In modern moral thinking, obligation is something every responsible person is supposed to have, but it is not an obligation to the state, or society, or humanity, or even to God. It is an obligation standing by itself. | |
| From: Richard Taylor (Virtue Ethics: an Introduction [2002], Ch.12) | |
| A reaction: This nicely pinpoints how some our moral attitudes are relics of religion. Taylor wants a return to virtue, but one could respond by opting for the social contract (with very clear obligations) or Kantian 'contractualism' (answering to rational beings). |
| 5066 | If we are made in God's image, pursuit of excellence is replaced by duty to obey God [Taylor,R] |
| Full Idea: Once people are declared to be images of God, just by virtue of minimal humanity, they have, therefore, no greater individual excellence to aspire to, and their purpose became one of obligation, that is, obedience to God's will. | |
| From: Richard Taylor (Virtue Ethics: an Introduction [2002], Ch.2) | |
| A reaction: An interesting and plausible historical analysis. There is a second motivation for the change, though, in Grotius's desire to develop a more legalistic morality, focusing on actions rather than character. Taylor's point is more interesting, though. |
| 5065 | The ethics of duty requires a religious framework [Taylor,R] |
| Full Idea: The ethics of duty cannot be sustained independently of a religious framework. | |
| From: Richard Taylor (Virtue Ethics: an Introduction [2002], Ch.2) | |
| A reaction: This is a big challenge to Kant, echoing Nietzsche's jibe that Kant just wanted to be 'obedient'. The only options are either 'natural duties', or 'duties of reason'. Reason may have a pull (like pleasure), but a 'duty'? Difficult. |
| 22230 | Sartre gradually realised that freedom is curtailed by the weight of situation [Sartre, by Daigle] |
| Full Idea: Sartre evolved from a notion of absolute freedom to one that truly takes into account the weight of situation. | |
| From: report of Jean-Paul Sartre (works [1950]) by Christine Daigle - Jean-Paul Sartre 2.3 | |
| A reaction: This change seems to have come much later, in the 1960s. The main influence seems to have been Marxism, which claims that consciousness is created by society, rather than by free individuals. |