The three rules for complex systems:

• a rule of generation
• a rule of reduction
• a rule of maintenance (or a tendency to persist)

Erik Christensen identifies six process categories (Christensen 2004, 97):

1. rule-determined transformation processes
2. goal-directed transformation processes
3. indeterminate transformation processes
4. rule-determined generative processes
5. goal-directed, and generative processes
6. indeterminate generative processes