Problem structuring methods (PSMs) are a group of techniques used to model or to map the nature or structure of a situation or state of affairs that some people want to change. PSMs are usually used by a group of people in collaboration (rather than by a solitary individual) to create a consensus about, or at least to facilitate negotiations about, what needs to change. Some widely adopted PSMs include soft systems methodology, the strategic choice approach, and strategic options development and analysis (SODA). Problem structuring methods (PSMs) are a group of techniques used to model or to map the nature or structure of a situation or state of affairs that some people want to change. PSMs are usually used by a group of people in collaboration (rather than by a solitary individual) to create a consensus about, or at least to facilitate negotiations about, what needs to change. Some widely adopted PSMs include soft systems methodology, the strategic choice approach, and strategic options development and analysis (SODA). Unlike some problem solving methods that assume that all the relevant issues and constraints and goals that constitute the problem are defined in advance or are uncontroversial, PSMs assume that there is no single uncontested representation of what constitutes the problem. PSMs are mostly used with groups of people, but PSMs have also influenced the coaching and counseling of individuals. The term 'problem structuring methods' as a label for these techniques began to be used in the 1980s in the field of operations research, especially after the publication of the book Rational Analysis for a Problematic World: Problem Structuring Methods for Complexity, Uncertainty and Conflict. Some of the methods that came to be called PSMs had been in use since the 1960s. Thinkers who later came to be recognized as significant early contributors to the theory and practice of PSMs include: In discussions of problem structuring methods, it is common to distinguish between two different types of situations that could be considered to be problems. Rittel and Webber's distinction between tame problems and wicked problems (Rittel & Webber 1973) is a well known example of such types. The following table lists similar (but not exactly equivalent) distinctions made by a number of thinkers between two types of 'problem' situations, which can be seen as a continuum between a left and right extreme: Tame problems (or puzzles or technical challenges) have relatively precise, straightforward formulations that are often amenable to solution with some predetermined technical fix or algorithm. It is clear when these situations have changed in such a way that the problem can be called solved. Wicked problems (or messes or adaptive challenges) have multiple interacting issues with multiple stakeholders and uncertainties and no definitive formulation. These situations are complex and have no stopping rule and no ultimate test of a solution. PSMs were developed for situations that tend toward the wicked or 'soft' side, when methods are needed that assist argumentation about, or that generate mutual understanding of multiple perspectives on, a complex situation. Other problem solving methods are better suited to situations toward the tame or 'hard' side where a reliable and optimal solution is needed to a problem that can be clearly and uncontroversially defined.