A Brief Comparison Of Pollock's Defeasible Reasoning And Ranking Functions

In this paper two theories of defeasible reasoning, Pollock's account and my theory of ranking functions, are compared, on a strategic level, since a strictly formal comparison would have been unfeasible. A brief summary of the accounts shows their basic difference: Pollock's is a strictly computational one, whereas ranking functions provide a regulative theory. Consequently, I argue that Pollock's theory is normatively defective, unable to provide a theoretical justification for its basic inference rules and thus an independent notion of admissible rules. Conversely, I explain how quite a number of achievements of Pollock's account can be adequately duplicated within ranking theory. The main purpose of the paper, though, is not to settle a dispute with formal epistemology, but rather to emphasize the importance of formal methods to the whole of epistemology.     

The Structure of Instrumental Practical Reasoning

Standard views of instrumental practical reasoning often appeal just to an end-directed desire and a means-end belief. I argue that such accounts are insufficient when it comes to the practical lives of agents. Instead I offer a novel view of such reasoning, the heart of which is the addition of a normative belief concerning the desirability of the agent's end.     

Evaluating Practical Reasoning

In this paper, the defeasible argumentation scheme for practical reasoning (Walton 1990) is revised. To replace the old scheme, two new schemes are presented, each with a matching set of critical questions. One is a purely instrumental scheme, while the other is a more complex scheme that takes values into account. It is argued that a given instance of practical reasoning can be evaluated, using schemes and sets of critical questions, in three ways: by attacking one or more premises of the argument, by attacking the inferential link between the premises and conclusion, or by mounting a counter-argument. It is argued that such an evaluation can be carried out in many cases using an argument diagram structure in which all components of the practical reasoning in the case are represented as premises, conclusions, and inferential links between them that can be labeled as argumentation schemes. This system works if every critical question can be classified as a assumption of or an exception to the original argument. However, it is also argued that this system does not work in all cases, namely those where epistemic closure is problematic because of intractable disputes about burden of proof.     

Monotonicity in Practical Reasoning

Classic deductive logic entails that once a conclusion is sustained by a valid argument, the argument can never be invalidated, no matter how many new premises are added. This derived property of deductive reasoning is known as monotonicity. Monotonicity is thought to conflict with the defeasibility of reasoning in natural language, where the discovery of new information often leads us to reject conclusions that we once accepted. This perceived failure of monotonic reasoning to observe the defeasibility of natural-language arguments has led some philosophers to abandon deduction itself (!), often in favor of new, non-monotonic systems of inference known as `default logics'. But these radical logics (e.g., Ray Reiter's default logic) introduce their desired defeasibility at the expense of other, equally important intuitions about natural-language reasoning. And, as a matter of fact, if we recognize that monotonicity is a property of the form of a deductive argument and not its content (i.e., the claims in the premise(s) and conclusion), we can see how the common-sense notion of defeasibility can actually be captured by a purely deductive system.     

Desires in Practical Reasoning

Inferences from desired ends to intended necessary means seem to be among the most unproblematic elements of practical reasoning. A closer look dissolves this appearance, however, when we see that such inferences are defeasible. We can nevertheless understand such inferences as leading to the adoption of plans, by analogy with inferences leading to explanations. Plans should satisfy at least some important ends desired by the agent, be consistent with the satisfaction of other desired ends, and be inconsistent with as few desired ends as possible. A rational plan may rule out the satisfaction of some desires, however, and this feature explains the defeasibility of such inferences.     

Practical Reasoning and the First Person

Philosophia - I argue that while practical reasoning is essentially first personal it does not require having essentially first personal thoughts. I start with an example of good practical...     

Rules of Meaning and Practical Reasoning

Can there be rules of language which serve both to determine meaning and to guide speakers in ordinary linguistic usage, i.e., in the production of speech acts? We argue that the answer is no. We take the guiding function of rules to be the function of serving as reasons for actions, and the question of guidance is then considered within the framework of practical reasoning. It turns out that those rules that can serve as reasons for linguistic utterances cannot be considered as normative or meaning determining. Acceptance of such a rule is simply equivalent to a belief about meaning, and does not even presuppose that meaning is determined by rules. Rules that can determine meaning, on the other hand, i.e., rules that can be regarded as constitutive of meaning, are not capable of guiding speakers in the ordinary performance of speech acts.     

Foundations of Everyday Practical Reasoning

“Since today is Saturday, the grocery store is open today and will be closed tomorrow; so let’s go today”. That is an example of everyday practical reasoning—reasoning directly with the propositions that one believes but may not be fully certain of. Everyday practical reasoning is one of our most familiar kinds of decisions but, unfortunately, some foundational questions about it are largely ignored in the standard decision theory: (Q1) What are the decision rules in everyday practical reasoning that connect qualitative belief and desire to preference over acts? (Q2) What sort of logic should govern qualitative beliefs in everyday practical reasoning, and to what extent is that logic necessary for the purposes of qualitative decisions? (Q3) What kinds of qualitative decisions are always representable as results of everyday practical reasoning? (Q4) Under what circumstances do the results of everyday practical reasoning agree with the Bayesian ideal of expected utility maximization? This paper proposes a rigorous decision theory for answering all of those questions, which is developed in parallel to Savage’s (1954) foundation of expected utility maximization. In light of a new representation result, everyday practical reasoning provides a sound and complete method for a very wide class of qualitative decisions; and, to that end, qualitative beliefs must be allowed to be closed under classical logic plus a well-known nonmonotonic logic—the so-called system ?.     

Normative Practical Reasoning: Christian Pillar

In the first part I discuss the thesis, advanced by John Broome, that intentions are normatively required by all-things-considered judgments about what one ought to do. I endorse this thesis, but remain sceptical about Broome's programme of grounding the correctness of reasoning in formal relations between contents of mental states. After discussing objections to the thesis, I concentrate in the second part on the relation between rational action and rational intention. I distinguish between content-related and attitude-related reasons for propositional attitudes like believing, wanting, and intending something. The former appeal to features of the content of the propositional attitude they are reasons for, the latter would be reasons for a propositional attitude because of features of the propositional attitude as a whole, for example the feature of its being beneficial to believe or to want that p . I try to show that the common philosophical reaction to attitude-related reasons, namely to claim that they are merely content-related reasons in disguise, is mistaken. In its most extreme form such a reaction would fail to respect the first-person character of reasoning which manifests itself in, among other things, the fact that a Moore-sentence and its analogue for intentions cannot be a conclusion of reasoning. In the third part I argue that there are attitude-related reasons for intentions, and, in showing how they influence practical deliberation, I find that their existence can be rendered compatible with the thesis that it is rational to intend to do what one thinks one ought to do.