Our research over the past few years demontrates reasonably well that shifts in choice following group decision making are rationally determined. This is to say, as a result of discussion the utilities of outcomes associated with alternative courses of action are revised; thus, the optimal individual choice, say, one which maximizes subjective expected utility, must (and does) shift correspondingly. The problem then becomes to explain how utilities, and thus choices, are so affected by discussion. We contended that utilities are revised because (1) the discussion elicits a broad range of persuasive-arguments for or against particular outcomes, and (2) these arguments were only partially available to the average member prior to discussion (the hypothesis of partially shared arguments). Our plan has been, first, to establish the validity of persuasive-arguments vis a vis other explanations of group decision effects; second, to generalize partially-shared-persuasive-argument theory to a variety of decision tasks (e.g., to decisions which do not involve risk or which normally elicit minimal discussion but perhaps a good deal of non-verbal argumentation); third, to extend the persuasive-argument hypothesis to more natural and thus relatively complex conditions (e.g., to consider the impact on decision-making of various arrays of arguments which have a particular organization and structure instead of dealing with a list of individual arguments, each with certain properties, as in our most recent research); fourth, to examine the relationship between the persuasiveness of certain common arguments and various social milieux (e.g., to explore the cultural roots of shared arguments and shifts in decision-making).