29 ideas
| 21793 | Genuine truth is the resolution of the highest contradiction [Hegel] |
| Full Idea: The highest truth, truth as such, is the resolution of the highest opposition and contradiction. | |
| From: Georg W.F.Hegel (Lectures on Aesthetics [1826], I: 99), quoted by Stephen Houlgate - An Introduction to Hegel 09 'Art' | |
| A reaction: Uneasy about the word 'highest', and the general Hegelian dream of 'resolving' contradictions, rather than just eliminating at least one component of them. No one else uses the word 'truth' like this. I suppose this Truth has a capital 'T'. |
| 21795 | What I hold true must also be part of my feelings and character [Hegel] |
| Full Idea: Whatever I hold as true, whatever ought to be valid for me, must also be in my feeling, must belong to my being and character. | |
| From: Georg W.F.Hegel (Lectures on Aesthetics [1826], I: 97), quoted by Stephen Houlgate - An Introduction to Hegel 09 'Philosophy' | |
| A reaction: I can see that truths do tend to become part of our character, but not that they ought to do so. I suppose I try to live my life enmeshed in the many truths which I have personally selected from the maelstrom of possibilities that engulf us. |
| 13520 | A 'tautology' must include connectives [Wolf,RS] |
| Full Idea: 'For every number x, x = x' is not a tautology, because it includes no connectives. | |
| From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 1.2) |
| 13524 | Deduction Theorem: T∪{P}|-Q, then T|-(P→Q), which justifies Conditional Proof [Wolf,RS] |
| Full Idea: Deduction Theorem: If T ∪ {P} |- Q, then T |- (P → Q). This is the formal justification of the method of conditional proof (CPP). Its converse holds, and is essentially modus ponens. | |
| From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 1.3) |
| 13522 | Universal Generalization: If we prove P(x) with no special assumptions, we can conclude ∀xP(x) [Wolf,RS] |
| Full Idea: Universal Generalization: If we can prove P(x), only assuming what sort of object x is, we may conclude ∀xP(x) for the same x. | |
| From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 1.3) | |
| A reaction: This principle needs watching closely. If you pick one person in London, with no presuppositions, and it happens to be a woman, can you conclude that all the people in London are women? Fine in logic and mathematics, suspect in life. |
| 13521 | Universal Specification: ∀xP(x) implies P(t). True for all? Then true for an instance [Wolf,RS] |
| Full Idea: Universal Specification: from ∀xP(x) we may conclude P(t), where t is an appropriate term. If something is true for all members of a domain, then it is true for some particular one that we specify. | |
| From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 1.3) |
| 13523 | Existential Generalization (or 'proof by example'): if we can say P(t), then we can say something is P [Wolf,RS] |
| Full Idea: Existential Generalization (or 'proof by example'): From P(t), where t is an appropriate term, we may conclude ∃xP(x). | |
| From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 1.3) | |
| A reaction: It is amazing how often this vacuous-sounding principles finds itself being employed in discussions of ontology, but I don't quite understand why. |
| 13529 | Empty Set: ∃x∀y ¬(y∈x). The unique empty set exists [Wolf,RS] |
| Full Idea: Empty Set Axiom: ∃x ∀y ¬ (y ∈ x). There is a set x which has no members (no y's). The empty set exists. There is a set with no members, and by extensionality this set is unique. | |
| From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 2.3) | |
| A reaction: A bit bewildering for novices. It says there is a box with nothing in it, or a pair of curly brackets with nothing between them. It seems to be the key idea in set theory, because it asserts the idea of a set over and above any possible members. |
| 13526 | Comprehension Axiom: if a collection is clearly specified, it is a set [Wolf,RS] |
| Full Idea: The comprehension axiom says that any collection of objects that can be clearly specified can be considered to be a set. | |
| From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 2.2) | |
| A reaction: This is virtually tautological, since I presume that 'clearly specified' means pinning down exact which items are the members, which is what a set is (by extensionality). The naïve version is, of course, not so hot. |
| 13534 | In first-order logic syntactic and semantic consequence (|- and |=) nicely coincide [Wolf,RS] |
| Full Idea: One of the most appealing features of first-order logic is that the two 'turnstiles' (the syntactic single |-, and the semantic double |=), which are the two reasonable notions of logical consequence, actually coincide. | |
| From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 5.3) | |
| A reaction: In the excitement about the possibility of second-order logic, plural quantification etc., it seems easy to forget the virtues of the basic system that is the target of the rebellion. The issue is how much can be 'expressed' in first-order logic. |
| 13535 | First-order logic is weakly complete (valid sentences are provable); we can't prove every sentence or its negation [Wolf,RS] |
| Full Idea: The 'completeness' of first order-logic does not mean that every sentence or its negation is provable in first-order logic. We have instead the weaker result that every valid sentence is provable. | |
| From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 5.3) | |
| A reaction: Peter Smith calls the stronger version 'negation completeness'. |
| 13531 | Model theory reveals the structures of mathematics [Wolf,RS] |
| Full Idea: Model theory helps one to understand what it takes to specify a mathematical structure uniquely. | |
| From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 5.1) | |
| A reaction: Thus it is the development of model theory which has led to the 'structuralist' view of mathematics. |
| 13532 | Model theory 'structures' have a 'universe', some 'relations', some 'functions', and some 'constants' [Wolf,RS] |
| Full Idea: A 'structure' in model theory has a non-empty set, the 'universe', as domain of variables, a subset for each 'relation', some 'functions', and 'constants'. | |
| From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 5.2) |
| 13519 | Model theory uses sets to show that mathematical deduction fits mathematical truth [Wolf,RS] |
| Full Idea: Model theory uses set theory to show that the theorem-proving power of the usual methods of deduction in mathematics corresponds perfectly to what must be true in actual mathematical structures. | |
| From: Robert S. Wolf (A Tour through Mathematical Logic [2005], Pref) | |
| A reaction: That more or less says that model theory demonstrates the 'soundness' of mathematics (though normal arithmetic is famously not 'complete'). Of course, he says they 'correspond' to the truths, rather than entailing them. |
| 13533 | First-order model theory rests on completeness, compactness, and the Löwenheim-Skolem-Tarski theorem [Wolf,RS] |
| Full Idea: The three foundations of first-order model theory are the Completeness theorem, the Compactness theorem, and the Löwenheim-Skolem-Tarski theorem. | |
| From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 5.3) | |
| A reaction: On p.180 he notes that Compactness and LST make no mention of |- and are purely semantic, where Completeness shows the equivalence of |- and |=. All three fail for second-order logic (p.223). |
| 13537 | An 'isomorphism' is a bijection that preserves all structural components [Wolf,RS] |
| Full Idea: An 'isomorphism' is a bijection between two sets that preserves all structural components. The interpretations of each constant symbol are mapped across, and functions map the relation and function symbols. | |
| From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 5.4) |
| 13539 | The LST Theorem is a serious limitation of first-order logic [Wolf,RS] |
| Full Idea: The Löwenheim-Skolem-Tarski theorem demonstrates a serious limitation of first-order logic, and is one of primary reasons for considering stronger logics. | |
| From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 5.7) |
| 13538 | If a theory is complete, only a more powerful language can strengthen it [Wolf,RS] |
| Full Idea: It is valuable to know that a theory is complete, because then we know it cannot be strengthened without passing to a more powerful language. | |
| From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 5.5) |
| 13525 | Most deductive logic (unlike ordinary reasoning) is 'monotonic' - we don't retract after new givens [Wolf,RS] |
| Full Idea: Deductive logic, including first-order logic and other types of logic used in mathematics, is 'monotonic'. This means that we never retract a theorem on the basis of new givens. If T|-φ and T⊆SW, then S|-φ. Ordinary reasoning is nonmonotonic. | |
| From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 1.7) | |
| A reaction: The classic example of nonmonotonic reasoning is the induction that 'all birds can fly', which is retracted when the bird turns out to be a penguin. He says nonmonotonic logic is a rich field in computer science. |
| 13530 | An ordinal is an equivalence class of well-orderings, or a transitive set whose members are transitive [Wolf,RS] |
| Full Idea: Less theoretically, an ordinal is an equivalence class of well-orderings. Formally, we say a set is 'transitive' if every member of it is a subset of it, and an ordinal is a transitive set, all of whose members are transitive. | |
| From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 2.4) | |
| A reaction: He glosses 'transitive' as 'every member of a member of it is a member of it'. So it's membership all the way down. This is the von Neumann rather than the Zermelo approach (which is based on singletons). |
| 13518 | Modern mathematics has unified all of its objects within set theory [Wolf,RS] |
| Full Idea: One of the great achievements of modern mathematics has been the unification of its many types of objects. It began with showing geometric objects numerically or algebraically, and culminated with set theory representing all the normal objects. | |
| From: Robert S. Wolf (A Tour through Mathematical Logic [2005], Pref) | |
| A reaction: His use of the word 'object' begs all sorts of questions, if you are arriving from the street, where an object is something which can cause a bruise - but get used to it, because the word 'object' has been borrowed for new uses. |
| 18549 | Nineteenth century aesthetics focused on art rather than nature (thanks to Hegel) [Hegel, by Scruton] |
| Full Idea: Only In the course of the nineteenth century, and in the wake of Hegel's posthumously published lectures on aesthetics, did the topic of art come to replace that of natural beauty as the core subject-matter of aesthetics. | |
| From: report of Georg W.F.Hegel (Lectures on Aesthetics [1826], 5) by Roger Scruton - Beauty: a very short introduction |
| 22043 | Hegel largely ignores aesthetic pleasure, taste and beauty, and focuses on the meaning of artworks [Hegel, by Pinkard] |
| Full Idea: Unlike his predecessors (including Kant), Hegel does not focus on aesthetic pleasure, nor on good taste, nor even on the nature and criteria for beauty. Instead he focuses on the meaning of artworks and their role in forming mankind's self-consciousness. | |
| From: report of Georg W.F.Hegel (Lectures on Aesthetics [1826]) by Terry Pinkard - German Philosophy 1760-1860 11 | |
| A reaction: Personally I dislike over-intellectualising art. The aim of a work of art is to give a certain experience, not to generate an ensuing sequence of theorising. I doubt whether Vermeer had any 'meaning' in mind in his obsessive work. |
| 22042 | Natural beauty is unimportant, because it doesn't show human freedom [Hegel, by Pinkard] |
| Full Idea: Hegel thinks that natural beauty is of no real significance since it cannot display our freedom to us; nature per se is meaningless. | |
| From: report of Georg W.F.Hegel (Lectures on Aesthetics [1826]) by Terry Pinkard - German Philosophy 1760-1860 11 | |
| A reaction: Presumably freedom is in the creation, and so creativity is what matters in aesthetics. But what are the criteria of good creativity? |
| 20413 | For Hegel the importance of art concerns the culture, not the individual [Hegel, by Eldridge] |
| Full Idea: Hegel locates the significance of art in its role in cultural life in general, not in relation to the psychological needs of individuals. | |
| From: report of Georg W.F.Hegel (Lectures on Aesthetics [1826]) by Richard Eldridge - G.W.F. Hegel (aesthetics) 1 | |
| A reaction: I'm beginning to see that art is a wonderful focus and test case for political attitudes. Roughly, liberalism focuses on individual responses, but more societal views (from right and left) see it in terms of role in the community. Which are you? |
| 20394 | The purpose of art is to reveal to Spirit its own nature [Hegel, by Davies,S] |
| Full Idea: According to Hegel, the goal of art was to serve as a phase in a process by which Spirit would come to understand its own nature. | |
| From: report of Georg W.F.Hegel (Lectures on Aesthetics [1826]) by Stephen Davies - The Philosophy of Art (2nd ed) 2.7 | |
| A reaction: I try very hard to understand ideas like this. Really really hard. However, since I see little sign of 'Spirit' really understanding its own nature, I'm guessing that the project is not going well. |
| 21794 | The main purpose of art is to express the unity of human life [Hegel] |
| Full Idea: Art's primary function, for Hegel, is to give expression to the unity and wholeness of life - especially human life - that the contingencies of everyday existence frequently conceal. | |
| From: Georg W.F.Hegel (Lectures on Aesthetics [1826]), quoted by Stephen Houlgate - An Introduction to Hegel 09 'Beauty' | |
| A reaction: I don't find the view that human life is 'unified' and 'whole' vary illuminating, and I have no objection to art which reflects the fragmentary and unstable aspects of life. I suspect Hegel would just prefer it if life were a unity. |
| 20415 | Art forms a bridge between the sensuous world and the world of pure thought [Hegel] |
| Full Idea: Spirit generates out of itself works of fine art as the first reconciling middle term between pure thought and what is merely external, sensuous and transient - between finite natural reality and the infinite freedom of conceptual thinking. | |
| From: Georg W.F.Hegel (Lectures on Aesthetics [1826], p.8), quoted by Richard Eldridge - G.W.F. Hegel (aesthetics) | |
| A reaction: This apparently says that there is necessarily an intellectual and conceptual component in art. This means little to me. Does he include portraits? Dutch domestic scenes? Would photography qualify? |
| 7903 | The six perfections are giving, morality, patience, vigour, meditation, and wisdom [Nagarjuna] |
| Full Idea: The six perfections are of giving, morality, patience, vigour, meditation, and wisdom. | |
| From: Nagarjuna (Mahaprajnaparamitashastra [c.120], 88) | |
| A reaction: What is 'morality', if giving is not part of it? I like patience and vigour being two of the virtues, which immediately implies an Aristotelian mean (which is always what is 'appropriate'). |