 A court may have to judge whether a defendant is liable for breach of contract on the basis of whether there was a valid contract in place and whether there was a breach. An expert panel may have to judge whether atmospheric greenhouse-gas concentrations will exceed a particular threshold by 2050, whether there is a causal chain from greater greenhouse-gas concentrations to temperature increases, and whether the temperature will increase. Legislators may have to judge whether a particular end is socially desirable, whether a proposed policy is the best means for achieving that end, and whether to pursue that policy.