A whole made of elements, the interconnections between them, and an overarching purpose or logic — the interactions, not the parts, are what define it.

Systems thinking (German Systemdenken) treats a thing not as a pile of parts but as an organised whole. Three ingredients have to be present:

• Elements — the components (people, organs, departments, variables).
• Interconnections — the relationships and flows that link the elements and let them influence one another.
• A purpose or governing logic — the system has its own "rules of the game" (the sociologist Niklas Luhmann called these Kommunikationslogiken, communication logics) that aren't reducible to any single part.

The decisive shift is the interconnections: a body is more than a heap of organs, a team more than a list of names. Rearrange the same elements with different relationships and you get a different system. That's why the field deliberately avoids one fixed, narrow definition — it's a transdisciplinary lens, borrowing from biology, medicine, physics, sociology and psychology, rather than a single theory.

Tip: A heap of bricks is not a house. Same elements, no interconnections, no purpose — no system.