WLODEK RABINOWICZ PREFERENCE STABILITY AND SUBSTITUTION OF INDIFFERENTS: A REJOINDER TO SEIDENFELD ABSTRACT. Seidenfeld (Seidenfeld, T. [1988a], Decision theory without ‘Inde- pendence’ or without ‘Ordering’, Economics and Philosophy 4: 267-290) gave an argument for Independence based on a supposition that admissibility of a sequential option is preserved under substitution of indifferents at choice nodes (S). To avoid a natural complaint that (S) begs the question against a critic of Independence, he provided an independent proof of (S) in his (Seidenfeld, T. [1988b], Rejoinder [to Hammond and McClennen], Economics and Philosophy 4: 309-315). In reply to my (Rabinowicz, W. [1995], To have one’s cake and eat it too: Sequential choice and expected-utility violations, The Journal of Philosophy 92: 586-620), in which I argue that the proof is invalid, Seidenfeld (Seidenfeld, T. [2000], Substitution of indifferent options at choice nodes and admissibility: A reply to Rabinowicz, Theory and Decision 48: 305–310 this issue) submits that I fail to give due consideration to one of the underlying assumptions of his derivation: it is meant to apply only to those cases in which the agent’s preferences are stable throughout the sequential decision process. The purpose of this note is to clarify the notion of preference stability so as meet this objection. KEY WORDS: Decision theory, Sequential decisions, Independence, Backward induction, Preferences, Indifference, Preference stability, Tiebreaks A REJOINDER TO SEIDENFELD Teddy Seidenfeld’s influential argument for Independence (Seiden- feld, 1988a) was based on the following substitution principle: (S) Admissibility of an option in a sequential decision problem is preserved under substitution at choice nodes of indifferent options. McClennen (1988) has objected to the use of this principle in an argument for Independence. According to him, this would be ques- tion begging. A theorist who rejects Independence denies that ad- missibility of options is invariably preserved under substitution of indifferents at chance nodes. Why would he need to accept that substitution of indifferents at choice nodes is any less problematic? Theory and Decision 48: 311–318, 2000. © 2000 Kluwer Academic Publishers. Printed in the Netherlands.