Efficient democratic decisions via nondeterministic proportional consensus One sentence summary: Novel, nonmajoritarian voting methods based on conditional commitments can achieve fairness without major welfare costs. Jobst Heitzig1∗ and Forest W Simmons2 1FutureLab on Game Theory and Networks of Interacting Agents, Potsdam Institute for Climate Impact Research, PO Box 60 12 03, D-14412 Potsdam, Germany 2Liberal Arts & Mathematics Division, Portland Community College, Cascade Campus, 705 N. Killingsworth Street, TH 220, Portland, OR 97217, USA ∗To whom correspondence should be addressed; E-mail:
[email protected]. Abstract: Are there voting methods which (i) give everyone, including minori- ties, an equal share of effective power even if voters act strategically, (ii) pro- mote consensus rather than polarization and inequality, and (iii) do not favour the status quo or rely too much on chance? We show the answer is yes by describing two nondeterministic voting meth- ods, one based on automatic bargaining over lotteries, the other on conditional commitments to approve compromise options. Our theoretical analysis and agent-based simulation experiments suggest that with these, majorities cannot consistently suppress minorities as with deterministic methods, proponents of arXiv:2006.06548v1 [econ.GN] 10 Jun 2020 the status quo cannot block decisions as in consensus-based approaches, the resulting aggregate welfare is comparable to existing methods, and average randomness is lower than for other nondeterministic methods. Majority rule, considered a cornerstone of democracy, allows the oppression of minorities — Tocqueville’s ‘tyranny of the majority’ (1) — which may lead to separatism or violent conflict (2, 3). One way to address this is the fundamental fairness principle of proportionality (e.g., (3, 4)).