Uncertainty plays an important role in The General Theory, particularly in the theory of interest rates. Keynes did not provide a theory of uncertainty, but he did make some enlightening remarks about the direction he thought such a theory should take. I argue that some modern innovations in the theory of probability allow us to build a theory which captures these Keynesian insights. If this is the right theory, however, uncertainty cannot carry its weight in Keynes’s arguments. This does not (...) mean that the conclusions of these arguments are necessarily mistaken; in their best formulation they may succeed with merely an appeal to risk. (shrink)

This dissertation looks at a set of interconnected questions concerning the foundations of probability, and gives a series of interconnected answers. At its core is a piece of old-fashioned philosophical analysis, working out what probability is. Or equivalently, investigating the semantic question of what is the meaning of ‘probability’? Like Keynes and Carnap, I say that probability is degree of reasonable belief. This immediately raises an epistemological question, which degrees count as reasonable? To solve that in its full generality would (...) mean the end of human inquiry, so that won’t be attempted here. Rather I will follow tradition and merely investigate which sets of partial beliefs are coherent. -/- The standard answer to this question, what is commonly called the Bayesian answer, says that degrees of belief are coherent iff they form a probability function. I disagree with the way this is usually justified, but subject to an important qualification I accept the answer. The important qualification is that degrees of belief may be imprecise, or vague. Part one of the dissertation, chapters 1 to 6, looks largely at the consequences of this qualification for the semantic and epistemological questions already mentioned. It turns out that when we allow degrees of belief to be imprecise, we can discharge potentially fatal objections to some philosophically attractive theses. Two of these, that probability is degree of reasonable belief and that the probability calculus provides coherence constraints on partial beliefs, have been mentioned. Others include the claim, defended in chapter 4, that chance is probability given total history. -/- As well as these semantic and epistemological questions, studies of the foundations of probability usually include a detailed discussion of decision theory. For reasons set out in chapter 2, I deny we can gain epistemological insights from decision theory. Nevertheless, it is an interesting field to study on its own, and it might be expected that there would be decision theoretic consequences of allowing imprecise degrees of belief. As I show in part two, this expectation seems to be mistaken. Chapter 9 shows that there aren’t interesting consequences of this theory for decision theory proper, and chapters 10 and 11 show that Keynes’s attempt to use imprecision in degrees of belief to derive a distinctive theory of interest rates is unsound. -/- Chapters 7 and 8 provide a link between these two parts. In chapter 7 I look at some previous philosophical investigations into the effects of imprecision. In chapter 8 I develop what I take to be the best competitor to the theory defended here – a constructivist theory of probability. On this view degrees of belief are precise, but the relevant coherence constraint is a constructivist probability calculus. This view is, I think, mistaken, but the calculus has some intrinsic interest, and there are at least enough arguments for it to warrant a chapter-length examination. (shrink)

Paul Davidson's critique of O'Driscoll and Rizzo is based on an “official” philosophical position that turns on an opposition between knowledge and ignorance and a corresponding opposition between ergodic and nonergodic processes. But Davidson's substantive analysis reveals a very different “unofficial” position, based on “sensible expectations” and a realist ontology of enduring social structures. While O'Driscoll and Rizzo have the edge on Davidson in terms of their characterization of agents’ beliefs, their ontology of event regularities is ultimately the same, and (...) suffers from the same drawbacks, as Davidson's official ontology. The solution to some of these problems may lie in adopting an ontology similar to the one Davidson invokes in his unofficial capacity. (shrink)

Ramsey's critique of Keynes's ‘logical’ approach to probability is widely regarded as decisive, and his own ‘subjective’ approach and SEU framework are now familiar tools in economics. This paper challenges the standard view of Ramsey's critique and assesses the SEU model from a Keynesian viewpoint on probability. It consists of a summary of the two theories and an evaluation of Ramsey's criticisms and alternative. The two main conclusions are that although Keynes yields to Ramsey on the question of the existence (...) of logical probability relations, the formal structure of his theory is compatible with non-objectivist interpretations of probability; and that Ramsey makes far heavier demands on the capacities of the ‘rational agent’ than does Keynes. (shrink)

The financial crisis that began in the US real-estate market in 2007 and culminated in a global economic slump showed bluntly how wrong financial risk models can be. This state of affairs has triggered a number of reactions and observations at the level of the specification and use of models and at a more conceptual/fundamental level. This article focuses on the epistemic features of such models – namely the nature, source, conditions of validity, structure and limits of the knowledge that (...) ‘well-specified’ models generate – so as to assess models in a balanced way, giving due weight to the fundamental determinants of their output and warning against overestimation of their possibilities; clarify the conditions under which models can be validly applied to economic and social relationships; render intelligible why the degree of accuracy that successful models would require is intrinsically unattainable; better understand models’ failure as evidenced by the crisis; and comment on the policy steps being undertaken to prevent similar financial crisis in the future. The analysis applies the principal tenets of critical realism to the daily preoccupations of risk management professionals and financial regulators alike. It is not intended as an intervention into critical realism. It draws on the works of Tony Lawson and Roy Bhaskar, and revisits relevant aspects of John Maynard Keynes’s work, connecting dots amongst them and marrying economic and philosophical analysis with day-to-day financial risk management and regulatory issues. Content Type Journal Article Category Article Pages 462-486 DOI 10.1558/jcr.v11i4.462 Authors Mattia L. Rattaggi, UBS/Cambridge Social Ontology Group Journal Journal of Critical Realism Online ISSN 1572-5138 Print ISSN 1476-7430 Journal Volume Volume 11 Journal Issue Volume 11, Number 4 / 2012. (shrink)

Weight of evidence continues to be a powerful metaphor within formal approaches to epistemology. But attempts to construe the metaphor in precise and useful ways have encountered formidable obstacles. This paper shows that two quite different understandings of evidential weight can be traced back to one 1878 article by C.S. Peirce. One conception, often associated with I.J. Good, measures the balance or net weight of evidence, while the other, generally associated with J.M. Keynes, measures the gross weight of evidence. Conflations (...) of these two notions have contributed to misunderstandings in the literature on weight. This paper shows why Peirce developed each conception of weight, why he distinguished them, and why they are easily mistaken for one another. (shrink)

Peirce makes it clear that doubt and belief oppose one another. But that slogan admits of a weaker and a stronger reading. The weaker reading permits and the stronger reading forbids one to be in a state of doubt and of belief with respect to the same proposition at the same time. The stronger claim is standardly attributed to Peirce, for textual and philosophical reasons. This paper maintains that this standard construal is excessively strong. It argues that the secondary literature (...) tends to presuppose the strong reading and that it often does so by confusing sufficient conditions for belief with necessary ones. It acknowledges some textual evidence on behalf of the strong reading but maintains that,taken as a whole, the relevant passages are as friendly to the weak as to the strong interpretation of Peirce. The paper then links the doubt–belief theory of“The Fixation of Belief” to the papers on probability that occupy the bulk of the Illustrations of the Logic of Science. It shows that Peirce's discussion of probability, strength of belief, and weight of evidence makes room for confidence, but not belief, to be undermined and thus offers a more flexible version of Peirce's theory of inquiry. (shrink)

Mainstream theories of decision making conceptualise uncertainty in terms of a well-defined probability distribution or weighting function. Following Knight, radical Keynesians consider subjective expected utility (SEU) theory and its variants as a restricted theory of decision-making applicable to situations of risk and, hence, of limited relevance to the understanding of crucial economic decisions under conditions of fundamental uncertainty in which probabilities are ill-defined, possibly non-existent. The objective of this paper is to outline a radical Keynesian theory of decision-making under uncertainty, (...) arguing that Keynes's suggestion to a two-dimensional probability-credence framework provides the basis for determining the limitations of mainstream approaches and points the way forward to the construction of a more general encompassing theory relevant to psychologists and economists outside of the Keynesian tradition. (shrink)

Marshall's asset equilibrium model provides a way of explaining the identity of entrepreneurs. Keynes adopted this model but transformed it when he emphasized the short-period and volatile character of long-term expectations. This entails a view of entrepreneur identity in which radical uncertainty plays a central role. This in turn deepens the post Keynesian view of uncertainty as ontological in that entrepreneurs' survival plays into their behavior. This paper explores this role-based view of individual identity and uses the analysis to comment (...) on Keynes’s ideas for the socialization of investment and euthanasia of the rentier in the last chapter of The general theory. (shrink)

Evidentialists say that a necessary condition of sound epistemic reasoning is that our beliefs reflect only our evidence. This thesis arguably conflicts with standard Bayesianism, due to the importance of prior probabilities in the latter. Some evidentialists have responded by modelling belief-states using imprecise probabilities (Joyce 2005). However, Roger White (2010) and Aron Vallinder (2018) argue that this Imprecise Bayesianism is incompatible with evidentialism due to “inertia”, where Imprecise Bayesian agents become stuck in a state of ambivalence towards hypotheses. Additionally, (...) escapes from inertia apparently only create further conflicts with evidentialism. This dilemma gives a reason for evidentialist imprecise probabilists to look for alternatives without inertia. I shall argue that Henry E. Kyburg’s approach offers an evidentialist-friendly imprecise probability theory without inertia, and that its relevant anti-inertia features are independently justified. I also connect the traditional epistemological debates concerning the “ethics of belief” more systematically with formal epistemology than has been hitherto done. (shrink)

The aim of this thesis is to improve our understanding of how to assess and communicate uncertainty in areas of research deeply afflicted by it, the assessment and communication of which are made more fraught still by the studies’ immediate policy implications. The IPCC is my case study throughout the thesis, which consists of three parts. In Part 1, I offer a thorough diagnosis of conceptual problems faced by the IPCC uncertainty framework. The main problem I discuss is the persistent (...) ambiguity surrounding the concepts of ‘confidence’ and ‘likelihood’; I argue that the lack of a conceptually valid interpretation of these concepts compatible with the IPCC uncertainty guide’s recommendations has worrying implications for both the IPCC authors’ treatment of uncertainties and the interpretability of the information provided in the AR5. Finally, I show that an understanding of the reasons behind the IPCC’s decision to include two uncertainty scales can offer insights into the nature of this problem. In Part 2, I review what philosophers have said about model-based robustness analysis. I assess several arguments that have been offered for its epistemic import and relate this discussion to the context of climate model ensembles. I also discuss various measures of independence in the climate literature, and assess the extent to which these measures can help evaluate the epistemic import of model robustness. In Part 3, I explore the notion of the ‘weight of evidence’ typically associated with Keynes. I argue that the Bayesian is bound to struggle with this notion, and draw some lessons from this fact. Finally, I critically assess some recent proposals for a new IPCC uncertainty framework that significantly depart from the current one. (shrink)