A decision-maker (DM) starts life as totally indecisive, and with time learns to order more pairs of alternatives, until their preferences become complete. On the basis of three well-documented behavioural regularities, we provide an axiomatisation of the evolution the DM’s preferences that results in a model of decreasing indecisiveness. In the resulting axiomatisation, the DM’s preferences at period t are given by a semi-order with threshold parameter σ(t), where σ(t) isa strictly decreasing function over time periods. We then introduce three simple heuristics that provide testable instances of the proposed model. We next study how two firms compete in a market consisting of a single indecisive consumer, thereby illustrating how preference formation may be shaped by strategic interactions between firms
