Rational Commitment and Legal Reason

38 Pages Posted: 18 Jun 2003 Last revised: 13 Jun 2008

See all articles by Bruce Chapman

Bruce Chapman

Faculty of Law, University of Toronto


Economic theory has a problem with the idea of rational commitment. It might be rational for an agent to make such a commitment (e.g., a threat, a promise) because the commitment makes alternatives available that are preferred by the agent to those alternatives that are available if no such commitment is made. Unfortunately, however, the same preference maximizing rationality that is sufficient to motivate the idea of making the commitment initially is often also sufficient to undermine the commitment when it comes time to carry it out. For example, it might be wasteful or contrary to one's preferences, and nothing more, to carry out a threat (promise) if the threat (promise) has been unsuccessful (successful) in deterring (inducing) another's behavior in the way that was planned. To the extent that this ex post quandary is predictable ex ante, the threat (promise) is not a credible one to make, either for the party threatened (promised) or for the threatening (promising) party. The result is that the benefits of being able to make such threats (promises) are lost.

In this paper I argue that what economic theory needs to resolve the problem of rational commitment is an account of rationality that is so structured that it can simultaneously comprehend both the preference maximizing rationality of adopting a commitment and the more formal (less substantive, less preference-based) rationality of carrying out the commitment once it has been made. The difficulty, of course, is that a rationality that is too formal, or rigid, in its adherence to the planned commitment ceases to look rational at all. Indeed, it appears to look more like blind commitment or mere mechanical habit, the sort of thing that takes the agent beyond the state of reflection or deliberation that is characteristic of rational behavior.

However, I argue in my paper that the required rational structure is to be found in some recent work by John Broome and, more particularly, in the sharp conceptual difference that Broome makes between action in accordance with reasons and action according to the normative requirements of practical rationality. Broome shows that it is a common mistake to think that all of rational behavior is action according to (undefeated) reasons and that this ignores the more formal constraints that fall under the normative requirements of practical rationality. I argue that the economic theory of rational choice falls prey to this same confusion (where reasons, whatever their basis, are ultimately thought to give rise to a preference for doing x rather than y, and rational choice consists in following that preference), something that serves to undermine the possibility of keeping to commitments rationally made. However, if there is more to rationality than acting for reasons, as Broome suggests with his account of normative requirements, then it is possible to be rational even as one acts contrary to reason in some particular case. In my paper I show the importance of this argument for the economic problem of rational commitment in general, and for the problem of credible threats and promises more particularly.

Lest this argument be thought of theoretical interest only, I also show that the more robust model of rational commitment that is made possible by the idea of normative requirements of practical rationality should be familiar to legal theorists. For it is an idea manifested constantly in common law decision-making, where defeasible legal rules, apparently simultaneously, both determine cases (as a matter of normative requirement) and are determined by them (as a matter of reason). Thus, the logical distinction between reasons and the normative requirements of practical rationality can be used both to prescribe a solution for a problem in rational choice, namely, the problem of rational commitment, and to provide understanding for what is rational in legal reason and the method of common law adjudication.

Keywords: practical rationality, reasons, rational choice, commitment, backward induction, centipede game, defeasibility, rules, legal reasoning, normative requirements

JEL Classification: A12, C70, C72, D90, K10, K40

Suggested Citation

Chapman, Bruce, Rational Commitment and Legal Reason. San Diego Law Review, Vol. 42, p. 91, 2005; U Toronto, Legal Studies Research Paper No. 03-02. Available at SSRN: https://ssrn.com/abstract=417081 or http://dx.doi.org/10.2139/ssrn.417081

Bruce Chapman (Contact Author)

Faculty of Law, University of Toronto ( email )

78 and 84 Queen's Park
Toronto, Ontario M5S 2C5
416-978-6911 (Phone)
416 978 2648 (Fax)

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