Boundaries define what issues are to be included, excluded or marginalized in analyses
(cognitive limits) and who is to be consulted or involved (social limits) (see MacGillivray,
2007; Midgley, 2008). Decisions on appropriate boundaries involve value judgments
grounded in an activity (Midgley, 2008). Effective boundary setting can reduce complexity
by limiting the range of available possibilities (Seidl, 2007). In this way, encouraging
discussion amongst suitable experts associated with the risk event, can broaden the
general possibilities of the social system, i.e. the number of risk events and their
consequences called secondary complexity; and reduce the number of unavailable
possibilities, i.e. the unknown or what Seidl (2007) calls ‘‘non-knowledge’’. In this way,
complexity theory from a system thinking perspective helps us understand how expert
discussion can increase the range of the known (available possibilities) and reduce the size
of the unknown (unavailable possibilities).