The Principle of Identity as Preserved Coherence Under Change

What allows something to remain the same while everything about it changes?

Across philosophy, biology, psychology, and systems theory, identity is constantly invoked but rarely defined with precision. Objects age, organisms replace their cells, systems are updated, people transform—yet we continue to speak of "the same" entity. This book addresses that unresolved problem directly.

The Principle of Identity as Preserved Coherence Under Change introduces a structural, domain-independent framework in which identity is not defined as a fixed essence, a narrative construction, or persistence in time. Instead, identity is understood as the preservation of coherence within bounded tolerance under successive change.

By shifting the focus from what something is to what it can carry, this work reframes three longstanding scientific problems: continuity without essence, identity without arbitrariness, and failure without normative judgement. Identity is neither static nor infinite. It holds as long as structural coherence can integrate change. When tolerance is exceeded, identity transforms or disappears—not as a moral failure, but as a structural consequence.

The principle is developed formally and then tested across multiple domains: physical systems, biological life, consciousness, social identity, and healthcare practice. Throughout, identity is treated as a structural criterion rather than a subjective experience or conventional label.

This book does not offer a new definition to add to existing theories. It proposes a different starting point. Identity is not what remains unchanged. Identity is what preserves coherence under change.