38 ideas
| 17749 | Post proved the consistency of propositional logic in 1921 [Walicki] |
| Full Idea: A proof of the consistency of propositional logic was given by Emil Post in 1921. | |
| From: Michal Walicki (Introduction to Mathematical Logic [2012], History E.2.1) |
| 17765 | Propositional language can only relate statements as the same or as different [Walicki] |
| Full Idea: Propositional language is very rudimentary and has limited powers of expression. The only relation between various statements it can handle is that of identity and difference. As are all the same, but Bs can be different from As. | |
| From: Michal Walicki (Introduction to Mathematical Logic [2012], 7 Intro) | |
| A reaction: [second sentence a paraphrase] In predicate logic you could represent two statements as being the same except for one element (an object or predicate or relation or quantifier). |
| 17764 | Boolean connectives are interpreted as functions on the set {1,0} [Walicki] |
| Full Idea: Boolean connectives are interpreted as functions on the set {1,0}. | |
| From: Michal Walicki (Introduction to Mathematical Logic [2012], 5.1) | |
| A reaction: 1 and 0 are normally taken to be true (T) and false (F). Thus the functions output various combinations of true and false, which are truth tables. |
| 17752 | The empty set is useful for defining sets by properties, when the members are not yet known [Walicki] |
| Full Idea: The empty set is mainly a mathematical convenience - defining a set by describing the properties of its members in an involved way, we may not know from the very beginning what its members are. | |
| From: Michal Walicki (Introduction to Mathematical Logic [2012], 1.1) |
| 17753 | The empty set avoids having to take special precautions in case members vanish [Walicki] |
| Full Idea: Without the assumption of the empty set, one would often have to take special precautions for the case where a set happened to contain no elements. | |
| From: Michal Walicki (Introduction to Mathematical Logic [2012], 1.1) | |
| A reaction: Compare the introduction of the concept 'zero', where special precautions are therefore required. ...But other special precautions are needed without zero. Either he pays us, or we pay him, or ...er. Intersecting sets need the empty set. |
| 17759 | Ordinals play the central role in set theory, providing the model of well-ordering [Walicki] |
| Full Idea: Ordinals play the central role in set theory, providing the paradigmatic well-orderings. | |
| From: Michal Walicki (Introduction to Mathematical Logic [2012], 2.3) | |
| A reaction: When you draw the big V of the iterative hierarchy of sets (built from successive power sets), the ordinals are marked as a single line up the middle, one ordinal for each level. |
| 17741 | To determine the patterns in logic, one must identify its 'building blocks' [Walicki] |
| Full Idea: In order to construct precise and valid patterns of arguments one has to determine their 'building blocks'. One has to identify the basic terms, their kinds and means of combination. | |
| From: Michal Walicki (Introduction to Mathematical Logic [2012], History Intro) | |
| A reaction: A deceptively simple and important idea. All explanation requires patterns and levels, and it is the idea of building blocks which makes such things possible. It is right at the centre of our grasp of everything. |
| 17747 | A 'model' of a theory specifies interpreting a language in a domain to make all theorems true [Walicki] |
| Full Idea: A specification of a domain of objects, and of the rules for interpreting the symbols of a logical language in this domain such that all the theorems of the logical theory are true is said to be a 'model' of the theory. | |
| From: Michal Walicki (Introduction to Mathematical Logic [2012], History E.1.3) | |
| A reaction: The basic ideas of this emerged 1915-30, but it needed Tarski's account of truth to really get it going. |
| 17748 | The L-S Theorem says no theory (even of reals) says more than a natural number theory [Walicki] |
| Full Idea: The L-S Theorem is ...a shocking result, since it implies that any consistent formal theory of everything - even about biology, physics, sets or the real numbers - can just as well be understood as being about natural numbers. It says nothing more. | |
| From: Michal Walicki (Introduction to Mathematical Logic [2012], History E.2) | |
| A reaction: Illuminating. Particularly the point that no theory about the real numbers can say anything more than a theory about the natural numbers. So the natural numbers contain all the truths we can ever express? Eh????? |
| 17761 | A compact axiomatisation makes it possible to understand a field as a whole [Walicki] |
| Full Idea: Having such a compact [axiomatic] presentation of a complicated field [such as Euclid's], makes it possible to relate not only to particular theorems but also to the whole field as such. | |
| From: Michal Walicki (Introduction to Mathematical Logic [2012], 4.1) |
| 17763 | Axiomatic systems are purely syntactic, and do not presuppose any interpretation [Walicki] |
| Full Idea: Axiomatic systems, their primitive terms and proofs, are purely syntactic, that is, do not presuppose any interpretation. ...[142] They never address the world directly, but address a possible semantic model which formally represents the world. | |
| From: Michal Walicki (Introduction to Mathematical Logic [2012], 4.1) |
| 17758 | Ordinals are transitive sets of transitive sets; or transitive sets totally ordered by inclusion [Walicki] |
| Full Idea: An ordinal can be defined as a transitive set of transitive sets, or else, as a transitive set totally ordered by set inclusion. | |
| From: Michal Walicki (Introduction to Mathematical Logic [2012], 2.3) |
| 17755 | Ordinals are the empty set, union with the singleton, and any arbitrary union of ordinals [Walicki] |
| Full Idea: The collection of ordinals is defined inductively: Basis: the empty set is an ordinal; Ind: for an ordinal x, the union with its singleton is also an ordinal; and any arbitrary (possibly infinite) union of ordinals is an ordinal. | |
| From: Michal Walicki (Introduction to Mathematical Logic [2012], 2.3) | |
| A reaction: [symbolism translated into English] Walicki says they are called 'ordinal numbers', but are in fact a set. |
| 17756 | The union of finite ordinals is the first 'limit ordinal'; 2ω is the second... [Walicki] |
| Full Idea: We can form infinite ordinals by taking unions of ordinals. We can thus form 'limit ordinals', which have no immediate predecessor. ω is the first (the union of all finite ordinals), ω + ω = sω is second, 3ω the third.... | |
| From: Michal Walicki (Introduction to Mathematical Logic [2012], 2.3) |
| 17760 | Two infinite ordinals can represent a single infinite cardinal [Walicki] |
| Full Idea: There may be several ordinals for the same cardinality. ...Two ordinals can represent different ways of well-ordering the same number (aleph-0) of elements. | |
| From: Michal Walicki (Introduction to Mathematical Logic [2012], 2.3) | |
| A reaction: This only applies to infinite ordinals and cardinals. For the finite, the two coincide. In infinite arithmetic the rules are different. |
| 17757 | Members of ordinals are ordinals, and also subsets of ordinals [Walicki] |
| Full Idea: Every member of an ordinal is itself an ordinal, and every ordinal is a transitive set (its members are also its subsets; a member of a member of an ordinal is also a member of the ordinal). | |
| From: Michal Walicki (Introduction to Mathematical Logic [2012], 2.3) |
| 13007 | Archimedes defined a straight line as the shortest distance between two points [Archimedes, by Leibniz] |
| Full Idea: Archimedes gave a sort of definition of 'straight line' when he said it is the shortest line between two points. | |
| From: report of Archimedes (fragments/reports [c.240 BCE]) by Gottfried Leibniz - New Essays on Human Understanding 4.13 | |
| A reaction: Commentators observe that this reduces the purity of the original Euclidean axioms, because it involves distance and measurement, which are absent from the purest geometry. |
| 17762 | In non-Euclidean geometry, all Euclidean theorems are valid that avoid the fifth postulate [Walicki] |
| Full Idea: Since non-Euclidean geometry preserves all Euclid's postulates except the fifth one, all the theorems derived without the use of the fifth postulate remain valid. | |
| From: Michal Walicki (Introduction to Mathematical Logic [2012], 4.1) |
| 17754 | Inductive proof depends on the choice of the ordering [Walicki] |
| Full Idea: Inductive proof is not guaranteed to work in all cases and, particularly, it depends heavily on the choice of the ordering. | |
| From: Michal Walicki (Introduction to Mathematical Logic [2012], 2.1.1) | |
| A reaction: There has to be an well-founded ordering for inductive proofs to be possible. |
| 17742 | Scotus based modality on semantic consistency, instead of on what the future could allow [Walicki] |
| Full Idea: The link between time and modality was severed by Duns Scotus, who proposed a notion of possibility based purely on the notion of semantic consistency. 'Possible' means for him logically possible, that is, not involving contradiction. | |
| From: Michal Walicki (Introduction to Mathematical Logic [2012], History B.4) |
| 23928 | Good art produces exaltation and detachment [Bell,C] |
| Full Idea: The contemplation of pure form leads to a state of extraordinary exaltation and complete detachment from the concerns of life. | |
| From: Clive Bell (Art [1913], I.III) | |
| A reaction: The last part is what gets the arts a bad name with the people who do deal with the concerns of life (which won't go away, even for an artist!). However, being totally trapped in the concerns of life is probably a recipe for misery. |
| 23922 | The word 'beauty' leads to confusion, because it denotes distinct emotions [Bell,C] |
| Full Idea: The word 'beauty' connotes objects of quite distinguishable emotions, and the term would land me in confusions and misunderstandings. | |
| From: Clive Bell (Art [1913], I.I) | |
| A reaction: His main example is a comparison of beautiful women with beautiful art. Personally I don't think the word aspires to be precise, so there is no problem. Maths has beautiful solutions, golf has beautiful shots, cooking has beautiful results. Wow! |
| 23921 | Our feeling for natural beauty is different from the aesthetic emotion of art [Bell,C] |
| Full Idea: It is not what I call an aesthetic emotion that most of us feel, generally, for natural beauty. …Most people feel a very different kind of emotion for birds, flowers and butterfly wings from that we feel for pictures, pots, temples and statues. | |
| From: Clive Bell (Art [1913], I.I) | |
| A reaction: Not convinced. I think the main difference is our awareness that art is a human production, the result of choice, whereas nature is a given. Beethoven 9 and a good sunset don't seem to me far apart in our responses. |
| 23929 | We only see landscapes as artistic if we ignore their instrumental value [Bell,C] |
| Full Idea: It is only when we cease to regard the objects in a landscape as means to anything that we can feel the landscape artistically. | |
| From: Clive Bell (Art [1913], II.I) | |
| A reaction: This sounds as if only the exploitative attitude blocks the artistic view, but I would expect the scientific view (of an ecologist, for example) to do the same. |
| 23923 | Visual form can create a sublime mental state [Bell,C] |
| Full Idea: Pure visual form transports me to an infinitely sublime state of mind. | |
| From: Clive Bell (Art [1913], I.I) | |
| A reaction: Unusual for anyone to use to term 'sublime' for works of art, and I suspect that Bell was the last to do so. Bell offers a quasi-religious role for art. I accept that being struck by something exceptionally good in art is a very distinctive experience. |
| 23932 | Art is the expression of an emotion for ultimate reality [Bell,C] |
| Full Idea: My hypothesis is that art is the expression of an emotion for ultimate reality. | |
| From: Clive Bell (Art [1913], II.II) | |
| A reaction: So later in his discussion the word 'ultimate' has crept in, after a chapter about the close relation between religious and artistic attitudes. He also sees good art as deeply 'spiritual'. It seems that religious belief is essential to his theory of art. |
| 23927 | Aestheticism invites artist to create beauty, but with no indication of how to do it [Bell,C] |
| Full Idea: The danger of aestheticism is that the artist who has got nothing to do but make something beautiful hardly knows where to begin or where to end | |
| From: Clive Bell (Art [1913], I.III) | |
| A reaction: Aestheticism strikes me as the main motivation for art nouveau artifacts, which I love. You start with beautiful lines, and then find ways to implement them. Bell has a point, though! |
| 8115 | Only artists can discern significant form; other people must look to art to find it [Bell,C, by Gardner] |
| Full Idea: Bell thinks that only artists can discern significant form directly in the natural world, and that all others must look to art for significant form. | |
| From: report of Clive Bell (Art [1913]) by Sebastian Gardner - Aesthetics 3.3 | |
| A reaction: I have a horrible feeling that 'significant' form will turn out to be the sort of form that artists can see. Presumably the form spotted by geologists won't be quite so 'significant'. Not a promising theory. |
| 23924 | Maybe significant form gives us a feeling for ultimate reality [Bell,C] |
| Full Idea: When we strip things of all associations and significance, what is left is 'the thing in itself', or 'ultimate reality'. …Artists can express an emotion felt for reality through line and colour. …So through 'significant form' we sense ultimate reality. | |
| From: Clive Bell (Art [1913], I.III) | |
| A reaction: [compressed] The thing in itself is a Kantian idea. He offers this as a speculation, rather than a fact. Maybe quantum physics gets us closer to the thing in itself? Bell knows that his faith in significant form needs more justification than an emotion. |
| 23931 | Significant form is the essence of art, which I believe expresses an emotion about reality [Bell,C] |
| Full Idea: My view that the essential quality in work of art is significant form was based on experience I am sure about. Of my view that significant form is the expression of a peculiar emotion felt for reality I am far from confident. | |
| From: Clive Bell (Art [1913], II.II) | |
| A reaction: It is hard to understand the idea of 'significant' form without a clear proposal for the nature of the significance. A detective doesn't stop at the point where evidence is seen as significant. Why should a 'peculiar' emotion matter? |
| 20434 | 'Form' is visual relations, and it is 'significant' if it moves us aesthetically; art needs both [Bell,C, by Feagin] |
| Full Idea: By 'form' Bell means the relations of lines, colours and shapes. Forms are 'significant' when the relationships of lines and so on move us aesthetically. If something is art it must have, to at least a minimum extent, significant form. | |
| From: report of Clive Bell (Art [1913], p.17) by Susan Feagin - Roger Fry and Clive Bell 3 | |
| A reaction: So art has two necessary conditions - that it move us aesthetically, and that it does so by means of its form. The obvious problem is to explain which forms are 'significant' without mentioning the aesthetic feeling they have to invoke. |
| 23934 | The only expression art could have is the emotion resulting from pure form [Bell,C] |
| Full Idea: If art expresses anything, it expresses an emotion felt for pure form and that which gives pure form its extraordinary significance. | |
| From: Clive Bell (Art [1913], III.I) | |
| A reaction: I don't think 'expresses' is the right word here. Artists express, but works just transmit. I personally doubt whether anything can have 'extraordinary significance' simply because it expresses one particular emotion. Why art, but not geometry? |
| 23925 | Mere copies of pictures are not significant - unless the copies are very exact [Bell,C] |
| Full Idea: A literal copy is seldom reckoned even by its owner a work of art. Its forms are not significant. Yet if it were an absolutely exact copy, clearly it would be as moving as the original, and a photographic reproduction of a drawing often is. | |
| From: Clive Bell (Art [1913], I.III) | |
| A reaction: What if the original artist made the copy? In 1913, Bell begins to spot this modern problem. He undermines his own theory of significant form here, if the form only becomes significant once we have checked it is an original. |
| 23926 | Art is distinguished by its aesthetic emotion, which produces appropriate form [Bell,C] |
| Full Idea: The characteristic of a work of art is its power of provoking aesthetic emotion; the expression of emotion is what gives it its power. ...Rightness of form is invariably a consequence of rightness of emotion. | |
| From: Clive Bell (Art [1913], I.III) | |
| A reaction: Bell doesn't dig very deep, because the obvious next question, not really addressed, is what makes the emotion 'right'. He suggests that significant form reveals reality, but why would an emotion do that? Does each work have a distinct emotion? |
| 23933 | Aesthetic contemplation is the best and most intense mental state [Bell,C] |
| Full Idea: Art is not only a means to good states of mind, but, perhaps, the best and most potent that we possess; …there is no state of mind more excellent or more intense than the state of aesthetic contemplation. | |
| From: Clive Bell (Art [1913], II.III) | |
| A reaction: Why does intensity make it good? It is pretty intense being involved in a road accident, but that doesn't make it good. There are many states of mind we enjoy or value highly, but we need more than that to prove them objectively 'excellent'. |
| 23935 | Aesthetic experience is an exaltation which increases the possibilities of life [Bell,C] |
| Full Idea: Those who have been thrilled by the pure aesthetic significance of a work of art …carry a state of excitement and exaltation making them more sensitive to all that is going forward about them. Thus they realise …the significance and possibility of life. | |
| From: Clive Bell (Art [1913], IV.III) | |
| A reaction: This seems like a bit of an afterthought, because he struggles to explain why his 'significant form' is so important. He shifts between it being an end - an intrinsic value - or a moral state, or now an increaser of life potential. |
| 22691 | Only artistic qualities matter in art, because they also have the highest moral value [Bell,C] |
| Full Idea: The only relevant qualities in art are artistic qualities: judged as a means to good, no other qualities are worth considering; for there are no qualities of greater moral value than artistic qualities, since there is no greater means to good than art. | |
| From: Clive Bell (Art [1913], II.III) | |
| A reaction: Wishful thinking, I suspect. I can't see anyone acquiring a moral education just by looking a Cezannes. This seems to be a late manifesto for the aesthetic movement. |
| 23930 | Religion sees infinite value in some things, and irrelevance in the rest [Bell,C] |
| Full Idea: The essence of religion is a conviction that because some things are of infinite value most are profoundly unimportant. | |
| From: Clive Bell (Art [1913], II.I) | |
| A reaction: The aspect of religion which most worries atheists like Nietzsche. You can end up with a rather cool and detached view of genocide, if you really believe that worldly matters are unimportant. Do souls in heaven worry about the next life after that? |