An ordered credibility contrast semantics for finite probability agreement

De Finetti's 1949 ordinal probability conjecture sparked enduring interest in intuitively meaningful necessary and sufficient conditions for orderings of finite propositional domains to agree with probability distributions. This paper motivates probabilistic ordering from subjective estimates of credibility contrasts revealed when ordered propositions are not monotonically related (e.g., A or B>C or D, but D>B) and when a portfolio of prospects is accepted as preferable to alternatives despite not dominating them. The estimated contrast primitive offers a gambling-free, psychologically grounded foundation for treating individual instances and multisets of propositions as credally interchangeable with disjunctions and multisets of their constituent atomic propositions.