Randomizing without randomness

We provide a methodology for eliciting utility midpoints from preferences, assuming that payoffs are consumption plans and that preferences satisfy a minimal form of additive separability. The methodology does not require any subjective or objective uncertainty. Thus, this construction of utility midpoints allows us to define mixtures of acts in a purely subjective fashion, without making any assumptions as to the decision maker’s reaction to the uncertainty that may be present. This approach makes it possible to provide a simple and fully subjective characterization of the second-order subjective expected utility model, allowing a clear distinction of such model from subjective expected utility.