Every system relies on selections (choices): body, psyche, groups, organisations, social functional systems. The body knows what tastes nice and what not, one knows who one loves and who not, groups know about the topics which can be discussed, organisations know their task and the legal system reacts to contraventions of the law. Selectivity, therefore, means the process, by which a system uses existing selections to strengthen them, discard them, vary them or to offer new choices. Existing references are dissolved and newly combined, the references are increased or reduced. This is important to understand: systems are not only selectively concerned with elements/events but also with the references (relations) and how these are linked with each other. Such relationships can also be called patterns, schemas, premises, culture, preferences, personality, group rules, team spirit or a thousand more concepts: all are phenomena which rely on selectivity. Selectivity reduces complexity, because it excludes most of the possibilities and usually only makes available a narrow range of decision-making possibilities to the system.