Metatickles and Death in Damascus

TL;DR

The paper addresses the problem of reconciling evidential and causal decision theories in Newcomb-type problems and, more challengingly, in decision-instability scenarios such as Death in Damascus. It extends Huttegger's metatickle framework by incorporating Skyrms' deliberative dynamics and a time-evolving independence dynamic, and then derives a plane of indifference that governs when deliberation preserves or changes action likelihoods. A central finding is that reconciliation is robust only under very particular conditions: the independence dynamics must not follow the shortest path to state-act independence, and the adaptive and independence dynamics must intersect the Eells-Jeffrey manifold at a precise point ($P(A2)=0.474$). While Newcomb can align evidential and causal prescriptions under these dynamics, Death in Damascus generally remains irresolute, illustrating limits to the metatickle approach for decision instability. The work provides a principled pre-analysis tool—the plane of indifference—to assess ex-ante whether reconciliation is plausible across a broad class of two-state, two-act problems, and it identifies key directions for future refinement of deliberative decision frameworks.$EU_{evid}(A)=\sum_i D(S_i\&A)P(S_i|A)$, $EU_{caus}(A)=\sum_i D(S_i\&A)P(S_i)$, and the plane $P(S2|A1)+P(S2|A2)=\frac{a-b-c}{a-b}$, with $P(A2)=0.474$ in the Death in Damascus setting. $

Abstract

The prescriptions of our two most prominent strands of decision theory, evidential and causal, differ in a general class of problems known as Newcomb problems. In these, evidential decision theory prescribes choosing a dominated act. Attempts have been made at reconciling the two theories by relying on additional requirements such as ratification (Jeffrey 1983) or "tickles" (Eells 1982). It has been argued that such attempts have failed (Lewis 1981a; Skyrms 1982). More recently, Huttegger (forthcoming) has developed a version of deliberative decision theory that reconciles the prescriptions of the evidentialist and causalist. In this paper, I extend this framework to problems characterised by decision instability, and show that it cannot deliver a resolute answer under a plausible specification of the tickle. I prove that there exists a robust method of determining whether the specification of the tickle matters for all two-state, two-act problems whose payoff tables exhibit some basic mathematical relationships. One upshot is that we have a principled way of knowing ex-ante whether a reconciliation of evidential and causal decision theory is plausible for a wide range of decision problems under this framework. Another upshot is that the tickle approach needs further work to achieve full reconciliation.

Figures (7)

• Figure 1: Diagrammatic depiction of Eells’ metatickle defence where the causal connection between act and state is erroneously drawn on the basis of the common cause
• Figure 2: Deliberative evidentialist reasoning under Huttegger's framework
• Figure 3: Evidentialist reasoning on the Eells-Jeffrey manifold
• Figure 4: Shortest path to Eells-Jeffrey manifold
• Figure 5: The plane of indifference