Online research in philosophy

Propositional dynamic logic (PDL) provides a natural setting for semantics of means-end relations involving non-determinism, but such models do not include probabilistic features common to much practical reasoning involving means and ends. We alter the semantics for PDL by adding probabilities to the transition systems and interpreting dynamic formulas 〈α〉 ϕ as fuzzy predicates about the reliability of α as a means to ϕ. This gives our semantics a measure of efficacy for means-end relations.

In my 1987 book I tried to understand intentions as, in the basic case, elements of larger and typically partial plans whose primary roles in our lives are ones of coordination and organization, both cross-temporal and social.1 I called this the planning theory of intention. Central to the planning theory is the idea that intentions – in contrast with ordinary desires -- are both embedded in characteristic regularities and are subject to distinctive rational pressures for consistency and coherence. There is, in particular, a rational demand that one’s intentions, taken together with one’s beliefs, fit together into a consistent model of one’s future. There is, further, a rational demand that one’s intentions be means-end coherent in the sense, roughly, that it not be true that one intends E, believes that E requires that one intend means M, and yet not intend M.3 And these norms of consistency and coherence are operative in a planning agent’s practical reasoning.

This paper seeks a better understanding of the elements of practical reasoning: premises and conclusion. It argues that the premises of practical reasoning do not normally include statements such as ‘I want to ϕ’; that the reasoning in practical reasoning is the same as in theoretical reasoning and that what makes it practical is, first, that the point of the relevant reasoning is given by the goal that the reasoner seeks to realize by means of that reasoning and the subsequent action; second, that the premises of such reasoning show the goodness of the action to be undertaken; third, that the conclusions of such reasoning may be actions or decisions, that can be accompanied by expressions of intention, either in action, or for the future; and that these are justified, and might be contradicted, in ways that are not only peculiar to them (i.e. in ways that diverge from those found in theoretical reasoning), but are distinctively practical, in that they involve reference to reasons for acting and to expressions of intention, respectively.1.

The requirements of instrumental rationality are often thought to be normative conditions on choice or intention, but this is a mistake. Instrumental rationality is best understood as a requirement of coherence on an agent's non-instrumental desires and means-end beliefs. Since only a subset of an agent's means-end beliefs concern possible actions, the connection with intention is thus more oblique. This requirement of coherence can be satisfied either locally or more globally, it may be only one among a number of such requirements on an agent's total set of desires and beliefs, and it has no special connection with reasoning. An appreciation of these facts leads to a better understanding of both the nature and the significance of instrumental rationality.

There has been considerable work on practical reasoning in artificial intelligence and also in philosophy. Typically, such reasoning includes premises regarding means–end relations. A clear semantics for such relations is needed in order to evaluate proposed syllogisms. In this paper, we provide a formal semantics for means–end relations, in particular for necessary and sufficient means–end relations. Our semantics includes a non-monotonic conditional operator, so that related practical reasoning is naturally defeasible. This work is primarily an exercise in conceptual analysis, aimed at clarifying and eventually evaluating existing theories of practical reasoning (pending a similar analysis regarding desires, intentions and other relevant concepts).

In this paper, I examine an account of instrumental reasoning recently put forth by John Broome. His key suggestion is that anyone who engages in reasoning about his intentions also believes that he will do what he intends to do and that combined with a belief about necessary means this creates rational pressure towards believing that one will take the necessary means. I argue that Broome’s model has three significant problems; his key premise is false—the sincere expression of an intention does not entail the belief that one will successfully execute that intention; his account yields a model of instrumental reasoning that is uncomfortably reflective; he seems unable to explain the rational pressure towards taking necessary means that arises directly from having an end and an instrumental belief. All three problems, I argue, are a consequence of Broome’s inadequate position on what it is to intend to do something.

The view to be defended in this paper is intended to be a novel and compelling model of instrumental practical reasoning, reasoning aimed at determining how to act in order to achieve a given end in a certain set of circumstances. On standard views of instrumental reasoning, the end in question is the object of a particular desire that the agent has, a desire which, when combined with the agent’s beliefs about what means are available to him or her in order to satisfy that desire, can cause the formation of an independent desire or intention to engage in the relevant means. One of the main goals in what follows is to show that such views provide an inadequate understanding of instrumental practical reasoning when it comes to the practical lives of agents. We shall proceed as follows. After some background assumptions are outlined in the next section, two important and largely neglected challenges will be raised to any view of instrumental practical reasoning (hereafter IP reasoning) which only countenances the role of end-directed desires and means-end beliefs in the mental economy of agents. In my view, neither of these challenges can be met, or at least not in any straightforward way. Hence the remainder of the paper is devoted to articulating and defending a new approach to understanding the structure of instrumental practical reasoning. The heart of this positive view will involve the addition of a normative belief concerning the desirability of the agent’s end.

Practical reasoning is a process of reasoning that concludes in an intention. One example is reasoning from intending an end to intending what you believe is a necessary means: 'I will leave the next buoy to port; in order to do that I must tack; so I'll tack', where the first and third sentences express intentions and the second sentence a belief. This sort of practical reasoning is supported by a valid logical derivation, and therefore seems uncontrovertible. A more contentious example is normative practical reasoning of the form 'I ought to φ, so I'll φ', where 'I ought to φ' expresses a normative belief and 'I'll φ' an intention. This has at least some characteristics of reasoning, but there are also grounds for doubting that it is genuine reasoning. One objection is that it seems inappropriate to derive an intention to φ from a belief that you ought to φ, rather than a belief that you ought to intend to φ. Another is that you may not be able to go through this putative process of reasoning, and this inability might disqualify it from being reasoning. A third objection is that it violates the Humean doctrine that reason alone cannot motivate any action of the will. This paper investigates these objections.

The view to be defended in this paper is intended to be a novel and compelling model of instrumental practical reasoning, reasoning aimed at determining how to act in order to achieve a given end in a certain set of circumstances. On standard views of instrumental reasoning, the end in question is the object of a particular desire that the agent has, a desire which, when combined with the agent’s beliefs about what means are available to him or her in order to satisfy that desire, can cause the formation of an independent desire or intention to engage in the relevant means. One of the main goals in what follows is to show that such views provide an inadequate understanding of instrumental practical reasoning when it comes to the practical lives of agents.

Practical reasoning is a process of reasoning that concludes in an intention. One example is reasoning from intending an end to intending what you believe is a necessary means: 'I will leave the next buoy to port; in order to do that I must tack; so I'll tack', where the first and third sentences express intentions and the second sentence a belief. This sort of practical reasoning is supported by a valid logical derivation, and therefore seems uncontrovertible. A more contentious example is normative practical reasoning of the form 'I ought to φ, so I'll φ', where 'I ought to φ' expresses a normative belief and 'I'll φ' an intention. This has at least some characteristics of reasoning, but there are also grounds for doubting that it is genuine reasoning. One objection is that it seems inappropriate to derive an intention to φ from a belief that you ought to φ, rather than a belief that you ought to intend to φ. Another is that you may not be able to go through this putative process of reasoning, and this inability might disqualify it from being reasoning. A third objection is that it violates the Humean doctrine that reason alone cannot motivate any action of the will. This paper investigates these objections.