Formal logic provides us with a powerful set of techniques for criticizing some arguments and showing others to be valid. These techniques are relevant to all of us with an interest in being skilful and accurate reasoners. In this highly accessible book, Peter Smith presents a guide to the fundamental aims and basic elements of formal logic. He introduces the reader to the languages of propositional and predicate logic, and then develops formal systems for evaluating arguments translated into these (...) languages, concentrating on the easily comprehensible 'tree' method. His discussion is richly illustrated with worked examples and exercises. A distinctive feature is that, alongside the formal work, there is illuminating philosophical commentary. This book will make an ideal text for a first logic course, and will provide a firm basis for further work in formal and philosophical logic. (shrink)
LO : John L. Bell, David DeVidi and Graham Solomon, Logical Options, Broadview Press, 2001. ILF : PeterSmith, Introduction to Formal Logic, CUP 2003. LFP : Ted Sider, Logic for Philosophy, OUP forthcoming: draft available at http://tedsider.org/books/lfp/lfp.pdf.
In 1931, the young Kurt Gödel published his First Incompleteness Theorem, which tells us that, for any sufficiently rich theory of arithmetic, there are some arithmetical truths the theory cannot prove. This remarkable result is among the most intriguing (and most misunderstood) in logic. Gödel also outlined an equally significant Second Incompleteness Theorem. How are these Theorems established, and why do they matter? Peter Smith answers these questions by presenting an unusual variety of proofs for the First Theorem, showing (...) how to prove the Second Theorem, and exploring a family of related results (including some not easily available elsewhere). The formal explanations are interwoven with discussions of the wider significance of the two Theorems. This book will be accessible to philosophy students with a limited formal background. It is equally suitable for mathematics students taking a first course in mathematical logic. (shrink)
My own philosophical interests led me to investigate the letter which Smith submitted to The Times, along with eighteen other signatures from renowned philosophers, each objecting to the honorary degree which Cambridge was about to award Jacques Derrida. While Smith's letter has been esteemed for sober defense of philosophy, it has also been viewed as rather notorious by Derrida and postmodern sympathizers. After having contacted Smith at the State University of New York at Buffalo, we agreed to meet and discuss (...) the matter in more detail. What follows are my inquiries, and his account, of his letter to The Times letters page, 9 May, 1992. (shrink)
When Adam Smith published his celebrated writings on economics and moral philosophy he famously referred to the operation of an invisible hand. Adam Smith's Political Philosophy makes visible the invisible hand by examining its significance in Smith's political philosophy and relating it to similar concepts used by other philosophers, revealing a distinctive approach to social theory that stresses the significance of the unintended consequences of human action. This book introduces greater conceptual clarity to the discussion of the invisible hand and (...) the related concept of unintended order in the work of Smith and in political theory more generally. By examining the application of spontaneous order ideas in the work of Smith, Hume, Hayek and Popper, Adam Smith's Political Philosophy traces similarities in approach and from these builds a conceptual, composite model of an invisible hand argument. While setting out a clear model of the idea of spontaneous order the book also builds the case for using the idea of spontaneous order as an explanatory social theory, with chapters on its application in the fields of science, moral philosophy, law and government. (shrink)
John E. Smith has contributed to contemporary philosophy in primarily four distinct capacities; first, as a philosopher of religion and God; second, as an indefatigable defender of philosophical reflection in its classical sense ( a sense inclusive of, but not limited to, metaphysics); third, as a participant in the reconstruction of experience and reason so boldly inaugurated by Hegel then redically transformed by the classical American pragmatists, and significantly augmented by such thinkers as Josiah Royce, william Earnest Hocking, and Alfred (...) North Whitehead; fourth, as an interpreter of philosophical texts and traditions (Kant, Hegel, and Nietzsche no less than Charles Peirce, WIlliam James and John Dewey; German idealism as well as American; the Augustinian tradition no less than the pragmatic). Reason, Experience, and God provides an important and comprehensive look at the work of John E. Smith by collected essays which each address aspects of his life-long work. A response by John E. Smith himself draws a line of continuity between the pieces. (shrink)
A collection of material on Husserl's Logical Investigations, and specifically on Husserl's formal theory of parts, wholes and dependence and its influence in ontology, logic and psychology. Includes translations of classic works by Adolf Reinach and Eugenie Ginsberg, as well as original contributions by Wolfgang Künne, Kevin Mulligan, Gilbert Null, Barry Smith, Peter M. Simons, Roger A. Simons and Dallas Willard. Documents work on Husserl's ontology arising out of early meetings of the Seminar for Austro-German Philosophy.
A realist theory of truth for a class of sentence holds that there are entities in virtue of which these sentences are true or false. We call such entities ‘truthmakers’ and contend that those for a wide range of sentences about the real world are moments (dependent particulars). Since moments are unfamiliar we provide a definition and a brief philosophical history, anchoring them in our ontology by showing that they are objects of perception. The core of our theory is the (...) account of truthmaking for atomic sentences, in which we expose a pervasive ‘dogma of logical form’, which says that atomic sentences cannot have more than one truthmaker. The authors uphold the mutual independence of logical and ontological complexity. The theory is compared with that of Wittgenstein’s Tractatus, and the authors outline formal principles of truthmaking taking account of both kinds of complexity and suggesting how to overcome Wittgenstein’s problem of negation. (shrink)
Philosophy in the West divides into three parts: Analytic Philosophy (AP), Continental Philosophy (CP), and History of Philosophy (HP). But all three parts are in a bad way. AP is sceptical about the claim that philosophy can be a science, and hence is uninterested in the real world. CP is never pursued in a properly theoretical way, and its practice is tailor-made for particular political and ethical conclusions. HP is mostly developed on a regionalist basis: what is studied is determined (...) by the nation or culture to which a philosopher belongs, rather than by the objective value of that philosopher’s work. Progress in philosophy can only be attained by avoiding these pitfalls. (shrink)
Experimental philosophers have gathered impressive evidence for the surprising conclusion that philosophers' intuitions are out of step with those of the folk. As a result, many argue that philosophers' intuitions are unreliable. Focusing on the Knobe Effect, a leading finding of experimental philosophy, we defend traditional philosophy against this conclusion. Our key premise relies on experiments we conducted which indicate that judgments of the folk elicited under higher quality cognitive or epistemic conditions are more likely to resemble those of the (...) philosopher. We end by showing how our experimental findings can help us better understand the Knobe Effect. (shrink)
... and a reading knowledge of formal logical symbolism is essential too. (Philosophers often use bits of logical symbolism to clarify their arguments.) Because the artificial and simply formal languages of logic give us highly illuminating objects of comparison when we come thinking about how natural languages work. (Relevant to topics in ‘philosophical logic’ and the philosophy of language.) But mainly because it us the point of entry into the study of one of the major intellectual achievements by philosophers of (...) the 20th – i.e. the development of mathematical logic. (Not least in Cambridge: Russell and Whitehead, Ramsey, Turing.). (shrink)
Theories of Theories of Mind brings together contributions by a distinguished international team of philosophers, psychologists, and primatologists, who between them address such questions as: what is it to understand the thoughts, feelings, and intentions of other people? How does such an understanding develop in the normal child? Why, unusually, does it fail to develop? And is any such mentalistic understanding shared by members of other species? The volume's four parts together offer a state of the art survey of the (...) major topics in the theory-theory/simulationism debate within philosophy of mind, developmental psychology, the aetiology of autism and primatology. The volume will be of great interest to researchers and students in all areas interested in the 'theory of mind' debate. (shrink)
Preface 1 The First Theorem revisited 1.1 Notational preliminaries 1.2 Definitional preliminaries 1.3 A general version of G¨ odel’s First Theorem 1.4 Giving the First Theorem bite 1.5 Generic G¨ odel sentences and arithmetic truth 1.6 Canonical and standard G¨ odel sentences 2 The Second Theorem revisited 2.1 Definitional preliminaries 2.2 Towards G¨ odel’s Second Theorem 2.3 A general version of G¨ odel’s Second Theorem 2.4 Giving the Second Theorem bite 2.5 Comparisons 2.6 Further results about provability predicates 2.7 Back (...) to the First Theorem 2.8 Introducing Rosserized provability predicates.. (shrink)
In a reading group, we’ve been working through the first three parts of Field’s Saving Truth from Paradox, by the end of which he has presented his core proposals. At this point, we’ve now rather lost the will to continue – for this is an astonishingly badly written book, which makes ridiculous demands on the patience of even a sympathetic reader. It so happened that it fell to me to introduce the last two chapters in Part III, Ch. 17 in (...) which Field rounds out his key technical construction, and Ch. 18, ‘What Has Been Done’. I talked mainly about the latter. Here, for what they are worth, are some very quickly written reflections on what has and hasn’t been achieved. (shrink)
This is a straightforward, elementary textbook for beginning students of philosophy. The general aim is to provide a clear introduction to the main issues arising in the philosophy of mind. Part I discusses the Cartesian dualist view which many find initially appealing, and contains a careful examination of arguments for and against. Part II introduces the broadly functionalist type of physicalism which has Aristotelian roots. This approach is developed to yield accounts of perception, action, belief and desire, and the emerging (...) theory of the mind is compared at each stage with rival historical and contemporary views. In Part III the functionalist approach is further explored in giving analyses of sensation, thought and freedom of will. The discussions throughout are exceptionally clear, and the writing uncomplicated, to make available to the students a wealth of detailed argument in the philosophy of mind. (shrink)
odel’s Theorems (CUP, heavily corrected fourth printing 2009: henceforth IGT ). Surely that’s more than enough to be going on with? Ah, but there’s the snag. It is more than enough. In the writing, as is the way with these things, the book grew far beyond the scope of the lecture notes from which it started. And while I hope the result is still pretty accessible to someone prepared to put in the time and effort, there is – to be (...) frank – a lot more in the book than is really needed by philosophers meeting the incompleteness theorems for the first time, or indeed by mathematicians wanting a brisk introduction. You might reasonably want to get your heads around only those technical basics which are actually necessary for understanding how the theorems are proved and for appreciating philosophical discussions about incompleteness. So you need a cut-down version of the book – an introduction to the Introduction! Well, isn’t that what lectures are for? Indeed. But there’s another snag. I haven’t got many lectures to play with. So either (A) I crack on at a very fast pace (hard-core mathmo style), cover those basics, but perhaps leave too many people puzzled and alarmed. Or (B) I do relaxed talk’n’chalk, highlighting the really Big Ideas, making sure everyone is grasping them as we go along, but inevitably omit important stuff and leave quite a gap between what happens in the lectures and what happens in the book. What to do? I’m going for plan (B). But then I ought to do something to fill that gap between lectures and book. Hence these notes. The idea, then, is to give relaxed lectures, highlighting Big Ideas, not worrying too much about depth or fine-detail (nor even about getting through all of the day’s intended menu of topics). These notes then expand things just enough, and give pointers to relevant chunks of IGT. Though I hope these notes will be to a fair extent be stand-alone, and tell a brief but coherent story read by themselves: so occasionally I’ll copy a paragraph or two from the book, rather than just refer to them.. (shrink)
Where to begin? I’ll take three books from my shelves. First, now nearly forty years old, a little book of television lectures by the great physicist Richard Feynman, The Character of Physical Law. He talks about the laws of motion, the inverse square law of gravitation, conservation laws, symmetry principles and the various ways these all hang together. Feynman obviously takes it that it is a prime aim of science to discover such laws. But what are laws? He writes – (...) and this is about his one and only shot at a characterization at the level of abstraction that we might think of as philosophical –. (shrink)
Many of our concepts are introduced to us via, and seem only to be constrained by, roughand-ready explanations and some sample paradigm positive and negative applications. This happens even in informal logic and mathematics. Yet in some cases, the concepts in question – although only informally and vaguely characterized – in fact have, or appear to have, entirely determinate extensions. Here’s one familiar example. When we start learning computability theory, we are introduced to the idea of an algorithmically computable function (...) (from numbers to numbers) – i.e. one whose value for any given input can be determined by a step-by-step calculating procedure, where each step is fully determined by some antecedently given finite set of calculating rules. We are told that we are to abstract from practical considerations of how many steps will be needed and how much ink will be spilt in the process, so long as everything remains finite. We are also told that each step is to be ‘small’ and the rules governing it must be ‘simple’, available to a cognitively limited calculating agent: for we want an algorithmic procedure, step-by-minimal-step, to be idiot-proof. For a classic elucidation of this kind, see e.g. Rogers (1967, pp. 1–5). Church’s Thesis, in one form, then claims this informally explicated concept in fact has a perfectly precise extension, the set of recursive functions. Church’s Thesis can be supported in a quasi-empirical way, by the failure of our searches for counterexamples. It can be supported too in a more principled way, by the observation that different appealing ways of sharpening up the informal chararacterization of algorithmic computability end up specifying the same set of recursive functions. But such considerations fall short of a demonstration of the Thesis. So is there a different argumentative strategy we could use, one that could lead to a proof? Sometimes it is claimed that there just can’t be, because you can never really prove results involving an informal concept like algorithmic computability.. (shrink)
This is an annotated reading list on the beginning elements of the theory of computable functions. It is now structured so as to complement the first eight lectures of Thomas Forster’s Part III course in Lent 2011 (see the first four chapters of his evolving handouts).
We are going to prove a key theorem that tells us just a bit more about the structure of the non-standard countable models of first-order Peano Arithmetic; and then we will very briefly consider whether any broadly philosophical morals can be drawn from the technical result. We’ll state the theorem after . .
Unlike his other major typescripts, the Big Typescript is divided into titled chapters, themselves divided into titled sections. But within a section we still get a collection of remarks typically without connecting tissue and lacking any transparently significant ordering or helpful signposting. So we still encounter the usual difficulties in trying to think our way through into what Wittgenstein might be wanting to say. Some enthusiasts like to try to persuade us that the aphoristic style is really of the essence. (...) But I’ve always wondered how true that is. So I here propose an experiment. Let’s take §108 of the ‘Big Typescript’ (the first of the sections in the part of the book titled ‘The Foundations of Mathematics’). There are four and a bit pages of remarks. I’m going to try to render them into rather more conventional prose. In the section that follows, then, I have embedded almost every sentence Wittgenstein wrote in his §108 – or rather, of course, I’ve embedded almost every sentence from the well-regarded translation. I have, however, often changed the order in which remarks appear, omitted some ‘and’s and ‘but’s and the like, changed some punctuation, demoted some passages to footnotes, but not – I hope – in any way that radically changes the significance of any remark, or distorts what is going on. And I’ve added a lot of signposting. I’ll comment, necessarily very briefly, on the results of the exercise starting in §3 below. So here we go . . (shrink)
In the opening chapter of ‘the Shorter Hodges’, we get a lot of fixing of terminology and notation, and some fairly natural definitions of ideas like that of isomorphism between structures. There are no really tricky ideas which need further exploration, nor any nasty proofs that could do with more elaboration. So I don’t pretend to have anything very thrilling by way of introductory comments. But let me make some more general philosophical comments.
Children’s ability to pretend, and the apparent lack of pretence in children with autism, have become important issues in current research on ‘theory of mind’, on the assumption that pretend play may be an early indicator of metarepresentational abilities.
In approaching Ch. 4 of Saving Truth from Paradox, it might be helpful first to revisit Curry’s original paper, and to revisit Lukasiewicz too, to provide more of the scenesetting that Field doesn’t himself fill in. So in §1 I’ll say something about Curry, in §2 we’ll look at what Lukasiewicz was up to in his original three-valued logic, and in §3 we’ll look at the move from a three-valued to a many-valued Lukasiewicz logic. In §4, I move on to (...) announce a theorem by H´. (shrink)
Publish or perish? Well, like it or not (and I for one don't!--for I fear it encourages narrowness and scholasticism), having a track record of pieces accepted for publication is now more or less a sine qua non for getting a foot on the first rung of the profession, as a junior research fellow or temporary lecturer. And when it comes to applying for a permanent lectureship a good track record of publication and clear evidence that you are going to (...) continue publishing is even more essential: UK departments attach a huge importance to their ratings in the Research Assessment Exercises, and good overseas departments place equal if not more weight on research promise. (shrink)
Like the other major journals, ANALYSIS can accept less than 10% of submissions. So standards are fierce. Many submissions are ruled out of court for being badly argued or for re-inventing the wheel or for being plain boring. But a fair proportion end up on the rejection pile simply because they are badly written. I saw far too much bad prose (to be sure, some of the prose that gets published is not exactly wonderful: I assure you that a lot (...) that doesn't get published is very much worse). (shrink)
The first main topic of this paper is a weak second-order theory that sits between firstorder Peano Arithmetic PA1 and axiomatized second-order Peano Arithmetic PA2 – namely, that much-investigated theory known in the trade as ACA0. What I’m going to argue is that ACA0, in its standard form, lacks a cogent conceptual motivation. Now, that claim – when the wraps are off – will turn out to be rather less exciting than it sounds. It isn’t that all the work that (...) has been done on ACA0 has been hopelessly misplaced: that would be a quite absurd suggestion. The mistake, if that’s what it is, has been a relatively small one. Still, we really ought to try to put things into conceptual good order here. That’s part of what philosophers are for. Here’s the structure of my main claim. On the one hand, interesting work on ACA0 actually only uses part of the strength of the theory: or as we might put it, the interesting work is actually carried on in a cut-down theory I’ll call ACA!. This theory, I’ll be claiming, does have a good conceptual motivation – it is in fact the theory that the putative conceptual grounding for ACA0 actually underpins. On the other hand, I’ll be arguing that original-strength ACA0 inductively inflates. I mean, to put it more carefully, that anyone who accepts ACA0 as a cogent theory can have no reason not to accept a certain significantly stronger theory, with a stronger induction principle. This stronger theory is standardly known as plain ACA. So, my claim comes to this: you can either go for the cut-down theory ACA!; or you can go for the much richer theory ACA. What you can’t do is – I mean, what you can’t have a stable conceptual motivation for doing – is to rest content with the intermediate strength ACA0 in its standard presentation. Yet in much of the literature, in particular in Simpson’s encyclopedic book Subsystems of Second-Order Arithmetic (1991), neither ACA! nor full ACA gets so much as a mention, and the conceptually unstable theory ACA0 gets all the glory. Why is my claim at all interesting? For at least two reasons.. (shrink)
Needless to say, Charles Parsons’s long awaited book1 is a must-read for anyone with an interest in the philosophy of mathematics. But as Parsons himself says, this has been a very long time in the writing. Its chapters extensively “draw on”, “incorporate material from”, “overlap considerably with”, or “are expanded versions of” papers published over the last twenty-five or so years. What we are reading is thus a multi-layered text with different passages added at different times. And this makes for (...) a rather bumpy read. There is another route Parsons could have taken: he could have reprinted the relevant papers with postscripts, and then top-and-tailed the collection with a preface and added concluding reflections. It must sound very ungrateful, but I rather suspect that that might have worked better. Much of the book is about arithmetic. But Parsons has woven into the discussion claims about mathematics more generally and about set theory in particular. We might well have a basic worry about this structure: for do defensible claims about the ontology and epistemology of arithmetic have to be generalizable to apply to more infinitary mathematics? For example, suppose you are attracted to a Hellman-like modal structuralist account of arithmetic: then should you think it a problem if you suspect that such an account can’t readily be extended to cope e.g. with set theory (since you boggle at the idea of possible worlds free of abstracta but with enough structure to somehow model ZFC)? Parsons himself seems to waver over such questions. So for present purposes, I’ll focus just on arithmetic, and in what follows I’ll revisit two of the most familiar Parsonian themes, his views on structuralism as an account of the ontology of arithmetic, and his exploration of the role of intuition in grounding arithmetical knowledge. (shrink)
• How to construct a ‘canonical’ Gödel sentence • If PA is sound, it is negation imcomplete • Generalizing that result to sound p.r. axiomatized theories whose language extends LA • ω-incompleteness, ω-inconsistency • If PA is ω-consistent, it is negation imcomplete • Generalizing that result to ω-consistent p.r. axiomatized theories which extend Q..
This is a straightforward, elementary textbook for beginning students of philosophy. The general aim is to provide a clear introduction to the main issues arising in the philosophy of mind. Part I discusses the Cartesian dualist view which many find initially appealing, and contains a careful examination of arguments for and against. Part II introduces the broadly functionalist type of physicalism which has Aristotelian roots. This approach is developed to yield accounts of perception, action, belief and desire, and the emerging (...) theory of the mind is compared at each stage with rival historical and contemporary views. In Part III the functionalist approach is further explored in giving analyses of sensation, thought and freedom of will. The discussions throughout are exceptionally clear, and the writing uncomplicated, to make available to the students a wealth of detailed argument in the philosophy of mind. (shrink)
In the section ‘Further reading’, I listed a book that arrived on my desk just as I was sending IGT off to the press, namely Church’s Thesis after 70 Years edited by Adam Olszewski et al. On the basis of a quick glance, I warned that the twenty two essays in the book did seem to be of ‘variable quality’. But actually, things turn out to be a bit worse than that: the collection really isn’t very good at all! After (...) I sent my book to press, I gave a paper-by-paper review on my blog, at http://logicmatters.blogspot.com. It is probably more fun to chase up the reviews ‘in the wild’, so to speak, starting from the entry for May 14, 2007. But here they are wrapped up into a single document, only marginally tidied. Some of the points made here should help further explain and support the general line on the Thesis taken in.. (shrink)
Here’s one version G¨ odel’s 1931 First Incompleteness Theorem: If T is a nice, sound theory of arithmetic, then it is incomplete, i.e. there are arithmetical sentences ϕ such that T proves neither ϕ nor ¬ϕ. There are three things here to explain straight away.
Theorem 1. If T is a sound formalized theory whose language contains the language of basic arithmetic, then there will be a true sentence GT of basic arithmetic such that T GT and ¬GT, so T must be negation incomplete.
I am interested in the philosophical prospects of what is called ‘predicativism given the natural numbers’. And today, in particular, I want to critically discuss one argument that has been offered to suggest that this kind of predicativism can’t have a stable philosophical motivation. Actually you don’t really need to know about predicativism to find some stand-alone interest in the theme I will be discussing. But still, it’s worth putting things into context. So I’m going to start by spending a (...) bit of time introducing you to the background. (shrink)
Timothy Smiley's wonderful paper 'Rejection' (Analysis 1996) is still perhaps not as well known or well understood as it should be. This note first gives a quick presentation of themes from that paper, though done in our own way, and then considers a putative line of objection - recently advanced by Julien Murzi and Ole Hjortland (Analysis 2009) - to one of Smiley's key claims. Along the way, we consider the prospects for an intuitionistic approach to some of the issues (...) discussed in Smiley's paper. (shrink)
In Episode 1, we introduced the very idea of a negation-incomplete formalized theory T . We noted that if we aim to construct a theory of basic arithmetic, we’ll ideally like the theory to be able to prove all the truths expressible in the language of basic arithmetic, and hence to be negation complete. But Gödel’s First Incompleteness Theorem says, very roughly, that a nice theory T containing enough arithmetic will always be negation incomplete. Now, the Theorem comes in two (...) flavours, depending on whether we cash out the idea of being ‘nice enough’ in terms of (i) the semantic idea of T ’s being a sound theory, or (ii) the idea of odel’s own T ’s being a consistent theory which proves enough arithmetic. And we noted that G¨. (shrink)
In the very last chapter of my Introduction to Gödel Theorems, I rashly claimed that there is a sense in which we can informally prove Church’s Thesis. This sort of claim isn’t novel to me: but it certainly is still very much the minority line. So maybe it is worth rehearsing some of the arguments again. Even if I don’t substantially add to the arguments in the book, it might help to approach things in a different order, with some different (...) emphases, to make the issue as clear as possible. (shrink)
An inertial frame is one in which a freely falling particle obeys Newton’s first law (i.e., continues in a state of uniform motion). Classically, we have the following: Galilean Principle of Relativity: The laws of dynamics are invariant between all inertial frames. In other words, all inertial observers (at rest in an inertial frame) will get experimentally verify the same dynamical laws.
Epiphenomenalism is a theory concerning the relation between the mental and physical realms, regarded as radically different in nature. The theory holds that only physical states have causal power, and that mental states are completely dependent on them. The mental realm, for epiphenomenalists, is nothing more than a series of conscious states which signify the occurrence of states of the nervous system, but which play no causal role. For example, my feeling sleepy does not cause my yawning — rather, both (...) the feeling and the yawning are effects of an underlying neural state. (shrink)
We’ve now proved our key version of the First Theorem, Theorem 42. If T is the right kind of ω-consistent theory including enough arithmetic, then there will be an arithmetic sentence GT such that T GT and T ¬GT. Moreover, GT is constructed so that it is true if and only if unprovable-in T (so it is true). Now recall that, for a p.r. axiomatized theory T , Prf T(m, n) is the relation which holds just if m (...) is the super g.n. of a sequence of wffs that is a T proof of a sentence with g.n. n. This relation is p.r. decidable (see §25.4). Assuming T extends Q, it can capture any p.r. decidable relation, including Prf T (§22). So we can define.. (shrink)
Why these notes? After all, I’ve written An Introduction to Gödel’s Theorems (CUP, heavily corrected fourth printing 2009: henceforth IGT ). Surely that’s more than enough to be going on with? Ah, but there’s the snag. It is more than enough. In the writing, as is the way with these things, the book grew far beyond the scope of the lecture notes from which it started. And while I hope the result is still pretty accessible to someone prepared to (...) put in the time and effort, there’s a lot more in the book than is really needed by philosophers meeting the incompleteness theorems for the first time. After all, you might want to get your heads around only those technical basics which are actually needed for understanding philosophical discussions about incompleteness. So you need a cut-down version of the book – an introduction to the Introduction! Well, isn’t that what lectures are for? Indeed. But there’s another snag. I haven’t got many lectures to play with. So either (A) I crack on at quite a fast pace (hard-core mathmo style), cover those basics, but perhaps leave too many people puzzled and alarmed. Or (B) I do relaxed talk’n’chalk, highlighting the really Big Ideas, making sure everyone is grasping them as we go along, but inevitably omit important stuff and leave quite a gap between what happens in the lectures and what happens in the book. What to do? I’m going for plan (B). But then I still need to do something to fill that gap between lectures and book. Hence these notes. The idea, then, is to give relaxed lectures, highlighting Big Ideas, not worrying too much about depth or fine-detail (or even about getting through all of the day’s intended menu of topics). Then after the lecture, I’ll write up notes that expand things just enough, and then give pointers to relevant chunks of IGT. The idea, however, is for the notes to be more or less stand-alone, and to tell a brief but coherent story read by themselves. So occasionally I’ll copy a paragraph or two from the book, rather than just refer to them. Warning: just occasionally in these notes, I’ll no doubt apply that good maxim ‘Where it doesn’t itch, don’t scratch’.. (shrink)
There is a familiar derivation of G¨ odel’s Theorem from the proof by diagonalization of the unsolvability of the Halting Problem. That proof, though, still involves a kind of self-referential trick, as we in effect construct a sentence that says ‘the algorithm searching for a proof of me doesn’t halt’. It is worth showing, then, that some core results in the theory of partial recursive functions directly entail G¨ odel’s First Incompleteness Theorem without any further self-referential trick.
Timothy Smiley’s wonderful paper ‘Rejection’ (1996) is still perhaps not as well known or well understood as it should be. This note first gives a quick presentation of themes from that paper, though done in our own way, and then considers a putative line of objection – recently advanced by Julien Murzi and Ole Hjortland (2009) – to one of Smiley’s key claims. Along the way, we consider the prospects for an intuitionistic approach to some of the issues discussed in (...) Smiley’s paper. (shrink)
Here is Hilbert is his famous address of 1900: The supply of problems in mathematics is inexhaustible, and as soon as one problem is solved numerous others come forth in its place. Permit me in the following, tentatively as it were, to mention particular definite problems, drawn from various branches of mathematics, from the discussion of which an advancement of science may be expected.
In the Wednesday Logic Reading Group, where we are working through Sara Negri and Jan von Plato’s Structural Proof Theory – henceforth ‘NvP’ – I today introduced Chapter 6, ‘Structural Proof Analysis of Axiomatic Theories’. In their commendable efforts to be brief, the authors are sometimes a bit brisk about motivation. So I thought it was worth trying to stand back a bit from the details of this action-packed chapter as far as I understood it in the few hours I (...) had to prepare, and to try to give an overall sense of the project. These are the notes I wrote for myself. As often with such middle-of-term efforts dashed off in a couple of hours, I both would have liked to do better and do more justice to what we are reading, but I also just don’t have time to do more now than make a few corrections to the first version. So the usual warning applies: caveat lector. (shrink)
In each of Parts 1A, IB and II of the Philosophy Tripos, there is an Essay paper in which you are asked to write for three hours on a single topic. In these notes I offer some suggestions about how to tackle this paper, and try to answer some Frequently Asked Questions. The notes are based (in the second half, very closely indeed) on notes written by Jane Heal -- I'm very grateful to her for allowing me to snaffle some (...) of her best suggestions, though she is not responsible for the final result. Do note, though, that the result is still just one view ... Consult other supervisors/directors of studies for additional advice. (shrink)
First-order Peano Arithmetic (PA) is incomplete. The question naturally arises: what kind of sentences of PA’s language LA (that’s ‘the language of basic arithmetic’, with the standard interpretation) can we establish to be true even though they are unprovable in PA?
Last week, we talked a bit about the Anderson-Belnap logic of entailment, as discussed in Priest’s Introduction to Non-Classical Logic. For a quite different approach to entailment, we’ll look next week at Neil Tennant’s account. Doing things rather out of order, this week I’d like to say something more basic about the problems to which both Anderson and Belnap, on the one hand, and Tennant on the other, are responding. This will give me the chance for a bit of nostalgic (...) philosophical time-travelling, revisiting work by Casimir Lewy and Timothy Smiley from the Cambridge of fifty years ago. (shrink)
This episode introduces the Second Incompleteness Theorem, says something about what it takes to prove it, and why it matters. Just two very quick reminders before we start. We said..
At the last meeting, Tim Crane gave a talk in which he made play with a distinction between ‘believing in’ and ‘believing that’. And he claimed that this distinction could be put to serious philosophical work of interest to serious metaphysicians. My hunch at the time was that this distinction in fact can’t bear any real weight. But I can’t now reconstruct Tim’s own arguments sufficiently to give a fair evaluation of them. However, Tim did say that the distinction he (...) wanted to draw, and at least some of the work to which he wanted to put the distinction, was grounded in a paper on ‘Believing in Things’ by Zolt´ an Szab´ o. So in this talk, I’ll see what we can get out of that paper. And, as far as I can recall Tim’s paper, I think it is fair to say the following. If Szab´. (shrink)
Why should we care about topoi so defined? Indeed, why should it be said that the idea of a topos is a sort of categorial generalization of the idea of a universe of sets? (By ‘categorial’ I mean a treatment where we give characteristics of the relevant objects and the mappings between them in terms of their relations to other objects and mappings belonging to the same category.).
In our preamble, it might be helpful this time to give a story about where we are going, rather than (as in previous episodes) review again where we’ve been. So, at the risk of spoiling the excitement, here’s what’s going to happen in this and the following three Episodes.
Sober (1992) has recently evaluated Brandon's (1982, 1990; see also 1985, 1988) use of Salmon's (1971) concept of screening-off in the philosophy of biology. He critiques three particular issues, each of which will be considered in this discussion.
Our last big theorem – Theorem 6 – tells us that if a theory meets certain conditions, then it must be negation incomplete. And we made some initial arm-waving remarks to the effect that it seems plausible that we should want theories which meet those conditions. Later, we announced that there actually is a consistent weak arithmetic with a first-order logic which meets the conditions (in which case, stronger arithmetics will also meet the conditions); but we didn’t say anything about (...) what such a weak theory really looks like. In fact, we haven’t looked at any detailed theory of arithmetic yet! It is high time, then, that we stop operating at the extreme level of abstraction of Episodes 1 and 2, and start getting our hands dirty. This Episode introduces a couple of weak arithmetics, before we tackle the canonical first-order arithmetic PA in the following instalment. By all means skip fairly lightly over some of the more boring proof details! But it is certainly worth getting just a flavour of how these two simple formal theories work. (shrink)
Arguably, there is no substantial, general answer to the question of what makes for the approximate truth of theories. But in one class of cases, the issue seems simply resolved. A wide class of applied dynamical theories can be treated as two-component theories—one component specifying a certain kind of abstract geometrical structure, the other giving empirical application to this structure by claiming that it replicates, subject to arbitrary scaling for units etc., the geometric structure to be found in some real-world (...) dynamical phenomenon. In such a case, a theory is approximately true just if the one geometric structure approximately replicates the other (and if problems remain here, they are problems in geometry, of specifying suitable metric approximation relations, not conceptual problems). This article amplifies and defends this simple approach to approximate truth for dynamical theories. (shrink)
The last Episode wasn’t about logic or formal theories at all: it was about common-or-garden arithmetic and the informal notion of computability. We noted that addition can be defined in terms of repeated applications of the successor function. Multiplication can be defined in terms of repeated applications of addition. The exponential and factorial functions can be defined, in different ways, in terms of repeated applications of multiplication. There’s already a pattern emerging here! The main task in the last Episode was (...) to get clear about this pattern. So first we said more about the idea of defining one function in terms of repeated applications of another function. Tidied up, that becomes the idea of defining a function by primitive recursion (Defn. 27). (shrink)
An Introduction to G¨ odel’s Theorems now exists in two versions – the original 2007 printing, and a corrected reprint in 2008. The quick way of telling these apart is to glance at the imprints page (the verso of the title page): the later version notes, halfway down that page, “Reprinted with corrections 2008”. Corrections marked with marginal side-bars as here are those that have been noted after the second printing went to press, and hence still need correction/improvement. If you (...) have the corrected reprint, then these marked corrections are the only errors you need care about! This complete list of corrections is divided, for convenience, into two sections. (shrink)
In a competitive, globalised world, corporate social responsibility (CSR) is proposed as a strategy to invigorate the competitiveness of small- and medium-sized enterprises (SMEs). The primary objective of this paper is to identify CSR factors that influence the competitiveness of SMEs and to develop a hypothesised model that can be tested on SMEs. Although SMEs in Uganda are increasingly becoming the backbone of the economy, their rate of survival and competitiveness are a cause for concern. The outcomes of CSR activities (...) can help to improve the survival rate of SMEs, and may offer great opportunities for business competitiveness, locally and globally. (shrink)
