45 ideas
| 8092 | Logic was merely a branch of rhetoric until the scientific 17th century [Devlin] |
| Full Idea: Until the rise of what we call the scientific method in the seventeenth century, logic was regarded largely as one aspect of rhetoric - a study of how one person't argument could convince another. | |
| From: Keith Devlin (Goodbye Descartes [1997], Ch.11) | |
| A reaction: This may well give the main reason why the Greeks invented logic in the first place. Aristotle wrote a book on rhetoric, and that was where the money was. Leibniz is clearly a key figure in the change of attitude. |
| 18390 | All metaphysical discussion should be guided by a quest for truthmakers [Armstrong] |
| Full Idea: My plea, whatever conclusions are drawn, is to control the metaphysical discussion by continual reference to suggested truthmakers. | |
| From: David M. Armstrong (Truth and Truthmakers [2004], 08.7) | |
| A reaction: ...And my plea is to control metaethical discussion by continual reference to value-makers. In general, this is the approach which will deliver a unified account of the world. Truthmakers are the ideal restraint on extravagant metaphysics. |
| 18467 | Truth-making can't be entailment, because truthmakers are portions of reality [Armstrong] |
| Full Idea: Truth-making cannot be any form of entailment. Both terms of an entailment relation must be propositions, but the truth-making term of the truth-making relation is a portion of reality, and, in general at least, portions of reality are not propositions. | |
| From: David M. Armstrong (Truth and Truthmakers [2004], 02.3) | |
| A reaction: Along with Idea 18466, that seems to firmly demolish the idea that truth-making is a logical entailment. |
| 18468 | Armstrong says truthmakers necessitate their truth, where 'necessitate' is a primitive relation [Armstrong, by MacBride] |
| Full Idea: In a bold manouevre Armstrong posited a metaphysically primitive relation of necessitation, and then defined truth-makers in terms of this bridging relation, as a thing that necessitates something being true. | |
| From: report of David M. Armstrong (Truth and Truthmakers [2004], 02.3) by Fraser MacBride - Truthmakers 1.2 | |
| A reaction: [Not sure of page reference] Spelled out so clearly by MacBride, this sounds dubious. How many truths are necessitated by the City of London? Do truthmakers necessitate the existence of their truths? MacBride says it's a circular theory. |
| 18377 | Negative truths have as truthmakers all states of affairs relevant to the truth [Armstrong] |
| Full Idea: Postulate a higher-order state of affairs, of all the states of affairs in which Theaetetus is involved. Is this not a good candidate for a truthmaker for the negative truth that 'Theaetetus is not flying'? | |
| From: David M. Armstrong (Truth and Truthmakers [2004], 05.2) | |
| A reaction: It certainly seems extravagant to need the whole universe to make true 'there are no lions in this room'. But for 'there are no unicorns' it is not clear which states of affairs unicorns are involved. (Armstrong is aware of this). |
| 18382 | The nature of arctic animals is truthmaker for the absence of penguins there [Armstrong] |
| Full Idea: Each of the arctic animals is by its nature different from a penguin, so this general state of affairs seems truthmaker enough for this negative existential. Similarly, the totality of all birds eliminates the phoenix. | |
| From: David M. Armstrong (Truth and Truthmakers [2004], 06.2) | |
| A reaction: Why is it 'animals' in one case, and 'birds' in the other? What if there was no life in arctic? Would the snow then do the job? This doesn't seem to work. |
| 18394 | In mathematics, truthmakers are possible instantiations of structures [Armstrong] |
| Full Idea: A mathematical entity exists if and only if it is possible that there be instantiations of that structure. This transforms the question of truthmakers for the existence of mathematical entities into a question of truthmakers for certain possibilities. | |
| From: David M. Armstrong (Truth and Truthmakers [2004], 09.3) | |
| A reaction: This modal approach to structuralism [for which he endorses Hellman 1989] opens up a modal approach to other truthmakers, which places dispositions at the centre of physical truthmaking. No sets of Meinongian objects? |
| 18384 | One truthmaker will do for a contingent truth and for its contradictory [Armstrong] |
| Full Idea: It seems reasonable to say that a truthmaker for a contingent truth is also a truthmaker for the truth that the contradictory of that truth is possible. | |
| From: David M. Armstrong (Truth and Truthmakers [2004], 07.2) | |
| A reaction: The truthmaker will have to be not only some fact, but also the additional fact that it is contingent, in order to generate the possibility of the contradictory. |
| 18387 | The truthmakers for possible unicorns are the elements in their combination [Armstrong] |
| Full Idea: The obvious minimal truthmaker for the truth that 'it is possible that a unicorn exists' is combinatorial. The elements of the combination are all that is needed. | |
| From: David M. Armstrong (Truth and Truthmakers [2004], 07.5) | |
| A reaction: This seems to imply that there are no possibilities which are not combinations of what currently exists. |
| 18386 | What is the truthmaker for 'it is possible that there could have been nothing'? [Armstrong] |
| Full Idea: It is possible that there could have been nothing. ...What would be its truthmaker? | |
| From: David M. Armstrong (Truth and Truthmakers [2004], 07.4) | |
| A reaction: I suppose the truthmaker here is the whole of reality, with its dispositions and contingencies. But that won't do for 'possibly there might never have been anything'. In such a case there wouldn't be any truths. |
| 18381 | Necessitating general truthmakers must also specify their limits [Armstrong] |
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Full Idea:
The mereological sum of what happens to be all the men does not necessitate that it is all the men. So if truthmaking involves necessitation, then this object cannot be the complete truthmaker for |
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| From: David M. Armstrong (Truth and Truthmakers [2004], 06.1) | |
| A reaction: [He invokes Russell has his source] His point is that the truthmaker needs a further fact, beyond the men, which specifies that this is all of them. But only if truthmakers necessitate their truths (as Armstrong claims). I'm sympathetic to both claims. |
| 8081 | 'No councillors are bankers' and 'All bankers are athletes' implies 'Some athletes are not councillors' [Devlin] |
| Full Idea: Most people find it hard to find any conclusion that fits the following premises: 'No councillors are bankers', and 'All bankers are athletes'. There is a valid conclusion ('Some athletes are not councillors') but it takes quite an effort to find it. | |
| From: Keith Devlin (Goodbye Descartes [1997], Ch. 2) | |
| A reaction: A nice illustration of the fact that syllogistic logic is by no means automatic and straightforward. There is a mechanical procedure, but a lot of intuition and common sense is also needed. |
| 8085 | Modern propositional inference replaces Aristotle's 19 syllogisms with modus ponens [Devlin] |
| Full Idea: Where Aristotle had 19 different inference rules (his valid syllogisms), modern propositional logic carries out deductions using just one rule of inference: modus ponens. | |
| From: Keith Devlin (Goodbye Descartes [1997], Ch. 4) | |
| A reaction: At first glance it sounds as if Aristotle's guidelines might be more useful than the modern one, since he tells you something definite and what implies what, where modus ponens just seems to define the word 'implies'. |
| 8086 | Predicate logic retains the axioms of propositional logic [Devlin] |
| Full Idea: Since predicate logic merely extends propositional logic, all the axioms of propositional logic are axioms of predicate logic. | |
| From: Keith Devlin (Goodbye Descartes [1997], Ch. 4) | |
| A reaction: See Idea 7798 for the axioms. |
| 18396 | The set theory brackets { } assert that the member is a unit [Armstrong] |
| Full Idea: The idea is that braces { } attribute to an entity the place-holding, or perhaps determinable, property of unithood. | |
| From: David M. Armstrong (Truth and Truthmakers [2004], 09.5) | |
|
A reaction:
I like this. There is Socrates himself, then there is my concept |
| 18393 | For 'there is a class with no members' we don't need the null set as truthmaker [Armstrong] |
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Full Idea:
The null class is useful in formal set theory, but I hope that does not require that there be a thing called the null class which is truthmaker for the strange proposition |
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| From: David M. Armstrong (Truth and Truthmakers [2004], 09.1) | |
| A reaction: It is not quite clear why it doesn't, but then it is not quite clear to philosophers what the status of the null set is, in comparison with sets that have members. |
| 8091 | Situation theory is logic that takes account of context [Devlin] |
| Full Idea: In many respects, situation theory is an extension of classical logic that takes account of context. | |
| From: Keith Devlin (Goodbye Descartes [1997], Ch. 8) | |
| A reaction: John Barwise is cited as the parent of this movement. Many examples show that logical form is very hard to pin down, because word-meaning depends on context (e.g. 'several crumbs' differs from 'several mountains'). |
| 8089 | Montague's intensional logic incorporated the notion of meaning [Devlin] |
| Full Idea: Montague's intensional logic was the first really successful attempt to develop a mathematical framework that incorporates the notion of meaning. | |
| From: Keith Devlin (Goodbye Descartes [1997], Ch. 8) | |
| A reaction: Previous logics, led by Tarski, had flourished by sharply dividing meaning from syntax, and concentrating on the latter. |
| 8087 | Golden ages: 1900-1960 for pure logic, and 1950-1985 for applied logic [Devlin] |
| Full Idea: The period from 1900 to about 1960 could be described as the golden age of 'pure' logic, and 1950 to 1985 the golden age of 'applied' logic (e.g. applied to everyday reasoning, and to theories of language). | |
| From: Keith Devlin (Goodbye Descartes [1997], Ch. 4) | |
| A reaction: Why do we always find that we have just missed the Golden Age? However this supports the uneasy feeling that the golden age for all advances in human knowledge is just coming to an end. Biology, including the brain, is the last frontier. |
| 8082 | Where a conditional is purely formal, an implication implies a link between premise and conclusion [Devlin] |
| Full Idea: Implication involves some form of link or causality between the antecedent and the consequent of an if-then; normally it says that the conclusion is a consequence of the premise (where conditionals are just defined by 'true' and 'false'). | |
| From: Keith Devlin (Goodbye Descartes [1997], Ch. 2) | |
| A reaction: This distinction is a key one when discussing 'If-then' sentences. Some are merely formal conditionals, but others make real claims about where you can get to from where you are. |
| 8072 | Sentences of apparent identical form can have different contextual meanings [Devlin] |
| Full Idea: "Safety goggles must be worn in the building" is clear enough, but "dogs must always be carried on the escalator" doesn't require us to head off in search of a dog. | |
| From: Keith Devlin (Goodbye Descartes [1997], Ch. 1) | |
| A reaction: A nice illustration of how the requirements of logical form will often take us beyond the strict and literal meaning of a sentence, into context, tone, allusion and subjective aspects. |
| 8075 | Space and time are atomic in the arrow, and divisible in the tortoise [Devlin] |
| Full Idea: The arrow paradox starts with the assumption that space and time are atomic; the tortoise starts with the opposite assumption that space and time are infinitely divisible. | |
| From: Keith Devlin (Goodbye Descartes [1997], Ch. 2) | |
| A reaction: Aquinas similarly covers all options (the cosmos has a beginning, or no beginning). The nature of movement in a space which involves quantum leaps remains metaphysically puzzling. Where is a particle at half of the Planck time? |
| 18392 | Classes have cardinalities, so their members must all be treated as units [Armstrong] |
| Full Idea: Classes, because they have a particular cardinality, are essentially a certain number of ones, things that, within the particular class, are each taken as a unit. | |
| From: David M. Armstrong (Truth and Truthmakers [2004], 09.1) | |
| A reaction: [Singletons are exceptions] So units are basic to set theory, which is the foundations of technical analytic philosophy (as well as, for many, of mathematics). If you can't treat something as a unit, it won't go into set theory. Vagueness... |
| 18385 | Logical atomism builds on the simple properties, but are they the only possible properties? [Armstrong] |
| Full Idea: One of the assumptions of logical atomism is that all structural properties, all complex properties, are composed of simple properties and relations. ...But does the totality of the simple properties consist of the only possible simple properties? | |
| From: David M. Armstrong (Truth and Truthmakers [2004], 07.3) | |
| A reaction: This refers to what Lewis calls 'alien' properties - possible properties that cannot even be constructed from actual properties. Armstrong's question is about the truthmakers for such things. A bit speculative... |
| 18391 | 'Naturalism' says only the world of space-time exists [Armstrong] |
| Full Idea: I define 'naturalism' as the hypothesis that the world of space-time is all that there is. | |
| From: David M. Armstrong (Truth and Truthmakers [2004], 09.1) | |
| A reaction: This is helpful, because it doesn't mention the nature of the physical matter contained in space-time, leaving theories like panpsychism as possible naturalistic theories. Galen Strawson, for example. |
| 18374 | Truthmaking needs states of affairs, to unite particulars with tropes or universals. [Armstrong] |
| Full Idea: There must exist states of affairs as truthmakers, to get us beyond 'loose and separate' entities. ...They can be bundles of tropes, or trope-with-particular, or bundles of universals ('compresence'), or instantiations. They are an addition to ontology. | |
| From: David M. Armstrong (Truth and Truthmakers [2004], 04.5) | |
| A reaction: Armstrong is the great champion of states of affairs. They seem rather vague to me, and disconcertingly timeless. |
| 18372 | We need properties, as minimal truthmakers for the truths about objects [Armstrong] |
| Full Idea: The 'thing itself' seems not be a minimal truthmaker for the thing having its particular mass. ...The thing has a great many other properties. ...It seems entirely reasonable to postulate that the object has properties that are objectively there. | |
| From: David M. Armstrong (Truth and Truthmakers [2004], 04.2) | |
| A reaction: This is Armstrong using the truthmaker principle to argue for the existence of properties (as instantiated universals). I like truthmakers, but truths do not have enough precision in their parts for us to read off reality from them. |
| 18379 | The determinates of a determinable must be incompatible with each other [Armstrong] |
| Full Idea: A set of determinates under the one determinable are incompatible by definition. If an object is not one mile in length, then its actual length will be incompatible with being one mile in length. | |
| From: David M. Armstrong (Truth and Truthmakers [2004], 05.2.1) | |
| A reaction: This is a much better general version of the standard example 'if it is red it can't be green'. Armstrong uses it to give a more precise account of incompatibility. Useful. |
| 18378 | Length is a 'determinable' property, and one mile is one its 'determinates' [Armstrong] |
| Full Idea: Length is a 'determinable' property; being some particular length, such as a mile, is one of its 'determinates'. | |
| From: David M. Armstrong (Truth and Truthmakers [2004], 05.2.1) | |
| A reaction: The seem to be 'type' and 'token' properties, except that this other vocabulary indicates the link between them. |
| 18373 | If tropes are non-transferable, then they necessarily belong to their particular substance [Armstrong] |
| Full Idea: 'Non-transferable' theories of tropes hold that the mass is of this stone by necessity. It is an identity condition for the property. Every property then becomes an essential property. | |
| From: David M. Armstrong (Truth and Truthmakers [2004], 04.3) | |
| A reaction: [He cites Martin and Heil for this view] It is hard to see in this proposal how the trope is in any way separate from its substance, and hence it seems a bit of a vacuous theory. (The other theories of properties aren't much cop either). |
| 18400 | Properties are not powers - they just have powers [Armstrong] |
| Full Idea: Properties are not powers. But properties have powers. They bestow powers. | |
| From: David M. Armstrong (Truth and Truthmakers [2004], 10.4) | |
| A reaction: I think this is the wrong way round. In this view, powers become extremely vague things, ranging from the fine-grained to the hugely broad. It seems to me that powers are precise and real, but properties are the vague unhelpful things. |
| 18397 | Powers must result in some non-powers, or there would only be potential without result [Armstrong] |
| Full Idea: Powers must surely issue in manifestations that are something more than just powers. A world where potency never issued in act, but only in more potency, would be one where one travelled without ever having the possibility of arriving. | |
| From: David M. Armstrong (Truth and Truthmakers [2004], 10.4) | |
| A reaction: Tricky. The picture I favour is that the distinction between powers and categorical properties is a misunderstanding. What is fundamental is active and powerful categoricals. |
| 18399 | How does the power of gravity know the distance it acts over? [Armstrong] |
| Full Idea: If masses are powers, the forces generated between two particulars have to vary inversely with the square of their distance apart. Have not the masses got to 'know' at what distance they are from each other, to exert the right amount of force? | |
| From: David M. Armstrong (Truth and Truthmakers [2004], 10.4) | |
| A reaction: This seems like a good warning against a simplistic account of powers doing all the work, but I suspect that more sophisticated physics would offer the fan of powers a solution here. The power is to 'spread' the force around. |
| 18371 | The class of similar things is much too big a truthmaker for the feature of a particular [Armstrong] |
| Full Idea: For a Class Nominalist 'the class of all 4-kilo objects' is the truthmaker for the truth that the particular has just that mass. Yet this looks far too big! Would not the object still be four kilos even if the other members of the class had never existed? | |
| From: David M. Armstrong (Truth and Truthmakers [2004], 04.2) | |
| A reaction: This seems so obvious to me as to be hardly worth saying. To identify redness with the class of red entities just seems crazy. Why do they belong in that class? Armstrong is illustrating the value of the truthmaker idea in philosophy. |
| 19347 | Substance needs independence, unity, and stability (for individuation); also it is a subject, for predicates [Perkins] |
| Full Idea: For individuation, substance needs three properties: independence, to separate it from other things; unity, to call it one thing, rather than an aggregate; and permanence or stability over time. Its other role is as subject for predicates. | |
| From: Franklin Perkins (Leibniz: Guide for the Perplexed [2007], 3.1) | |
| A reaction: Perkins is describing the Aristotelian view, which is taken up by Leibniz. 'Substance' is not a controversial idea, if we see that it only means that the world is full of 'things'. It is an unusual philosopher wholly totally denies that. |
| 18389 | When entities contain entities, or overlap with them, there is 'partial' identity [Armstrong] |
| Full Idea: There is 'partial identity' where one entity contains another with something to spare, or else where entities overlap each other. ...Extensive quantities, such as length and mass, are the particularly plausible cases. | |
| From: David M. Armstrong (Truth and Truthmakers [2004], 08.5) | |
| A reaction: This looks like a very useful concept which deserves wider use. It will help discussions of rivers, statues, intersecting roads etc. |
| 18388 | Possible worlds don't fix necessities; intrinsic necessities imply the extension in worlds [Armstrong] |
| Full Idea: It seems natural and plausible to say that it is the fact that a necessary truth is itself necessary that determines its truth in all possible worlds. This intension determines its extension across possible worlds. | |
| From: David M. Armstrong (Truth and Truthmakers [2004], 08.1) | |
| A reaction: Well said. To me (but not to Armstrong) this implies essentialism, that the necessity arises from the intrinsic natures of the things involved. The whole Lewisian approach of explaining things by mapping them strikes me as wrong. |
| 8088 | People still say the Hopi have no time concepts, despite Whorf's later denial [Devlin] |
| Full Idea: The Hopi time myth does not appear to have been stopped for a moment by the fact that Whorf himself subsequently wrote that the Hopi language does indeed have words for past, present, and future | |
| From: Keith Devlin (Goodbye Descartes [1997], Ch. 5) | |
| A reaction: Arguments for relativism based on the Hopi seem now to be thoroughly discredited. Sensible people never believed them in the first place. |
| 18375 | General truths are a type of negative truth, saying there are no more ravens than black ones [Armstrong] |
| Full Idea: General truths are a species of negative truth, 'no more' truths, asserting that there are no more men than the mortal ones, no more ravens than the black ones. | |
| From: David M. Armstrong (Truth and Truthmakers [2004], 05.1) | |
| A reaction: He goes on to distinguish between 'absences' and 'limits' in this area. |
| 8073 | How do we parse 'time flies like an arrow' and 'fruit flies like an apple'? [Devlin] |
| Full Idea: How do people identify subject and verb in the sentences "time flies like an arrow" and "fruit flies like an apple"? | |
| From: Keith Devlin (Goodbye Descartes [1997], Ch. 1) | |
| A reaction: A nice illustration of the fact that even if we have an innate syntax mechanism, it won't work without some semantics, and some experience of the environmental context of utterances. |
| 18368 | For all being, there is a potential proposition which expresses its existence and nature [Armstrong] |
| Full Idea: The thesis of 'expressibility' says that for all being, there is a proposition (perhaps one never formulated by any mind at any time) that truly renders the existence and nature of this being. | |
| From: David M. Armstrong (Truth and Truthmakers [2004], 02.3.2) | |
| A reaction: [He credits Stephen Read 2000:68-9 for this] Armstrong accepts this, but I deny it. I can't make any sense of this vast plethora of propositions, each exactly expressing some minute nuance of the infinity complexity of all being. |
| 18370 | A realm of abstract propositions is causally inert, so has no explanatory value [Armstrong] |
| Full Idea: We could not stand in any causal or nomic relation to a realm of propositions over and above the space-time world, ...so it is unclear that such a postulation is of any explanatory value. | |
| From: David M. Armstrong (Truth and Truthmakers [2004], 02.6) | |
| A reaction: I agree, and I like Armstrong's appeal to explanation as a criterion for whether we should make an ontological commitment here. I am baffled by anyone who thinks reality is crammed full of unarticulated propositions. Only a philosopher.... |
| 8076 | The distinction between sentences and abstract propositions is crucial in logic [Devlin] |
| Full Idea: The distinction between sentences and the abstract propositions that they express is one of the key ideas of logic. A logical argument consists of propositions, assembled together in a systematic fashion. | |
| From: Keith Devlin (Goodbye Descartes [1997], Ch. 2) | |
| A reaction: He may claim that arguments consist of abstract propositions, but they always get expressed in sentences. However, the whole idea of logical form implies the existence of propositions - there is something which a messy sentence 'really' says. |
| 18380 | Negative causations supervene on positive causations plus their laws? [Armstrong] |
| Full Idea: Is it not very plausible that negative causations supervene on the positive causations together with the laws that govern the positive causations? | |
| From: David M. Armstrong (Truth and Truthmakers [2004], 05.2.3) | |
| A reaction: This obviously has a naturalistic appeal, since all causation can then be based on the actual world. |
| 18401 | The pure present moment is too brief to be experienced [Armstrong] |
| Full Idea: The metaphysical present will be a strict instant, or, if time is not infinitely divisible, the present will be a minimum granule of duration. But strict instants or minimal granules of duration, if these exist, cannot be experienced. | |
| From: David M. Armstrong (Truth and Truthmakers [2004], 11) | |
| A reaction: He points out that this is ironic, since Presentism lies on the basic experience of the present. |