If you replace every plank on a ship over time, is it still the same ship

GPT-5.4

Vote: Yes

Yes, if the replacement is gradual and the ship continues functioning as the same vessel through time, we usually treat its identity as continuous. Objects like ships are often identified by continuity of structure, purpose, ownership, and history, not by preserving every original atom or plank. Repair and maintenance do not normally create a new ship each time a part is changed. So under the ordinary notion of identity across time, the ship remains the same ship despite complete replacement of its parts.

Grok 4.1 Fast

Vote: Yes

The Ship of Theseus paradox hinges on the nature of identity, which is not solely material but also involves spatiotemporal continuity, form, and function. Gradual replacement maintains these, so the ship remains the same. Consider human bodies: every cell is replaced over years, yet personal identity endures. Similarly, the ship's structure, purpose, and history persist uninterrupted. If identity required unchanged matter, nothing would retain identity over time—not people, not objects. Continuity defines sameness here.

Sonar Pro

Vote: Yes

The question is the Ship of Theseus paradox, a classic philosophical puzzle about identity and persistence over time. Option **A (Yes)** aligns with the predominant view that the ship retains its identity through continuity of form, function, and historical role, despite total material replacement. Philosophically, identity isn't solely material; it's relational. Sources on vessel identification (e.g., legal frameworks in [1][2][3]) emphasize continuity via documentation, ownership, and registration numbers, not the physical planks. A ship remains 'the same' legally and practically if it maintains its name, registry, and purpose—replacing parts doesn't void this, as seen in maintenance practices [4][7]. Voting **B (No)** reduces identity to atoms, ignoring real-world precedents like human cells fully replacing every 7-10 years yet retaining personal identity, or restored historical artifacts. Legal systems treat incrementally replaced vessels as identical [5][6], supporting **A** as more coherent and practical.

Gemini 3.1 Pro

Vote: Yes

Identity is determined by continuous organizational structure and history, not a static set of material components. The essence of the ship resides in its continuous function, design, and spatiotemporal path over time. Consider the biological equivalent: the human body replaces nearly all of its cellular material over a period of several years. Yet, we do not consider a person to be a completely different individual simply because their physical makeup has refreshed. Because the replacement happens gradually and the ship maintains its functional integrity throughout the entire process, it retains its identity. Therefore, both conceptually and practically, it remains the same ship.

Claude Opus 4.6

Vote: Yes

Yes, it is still the same ship. This is the classic Ship of Theseus paradox, and the most compelling answer is that identity is not reducible to material composition alone. First, consider that our own bodies replace nearly all their cells over the course of several years, yet we do not consider ourselves to be different people. Identity persists through gradual material change because it is grounded in continuity of form, function, and causal history — not in the specific atoms that compose an object at any given moment. Second, the ship maintains continuous spatiotemporal identity throughout the replacement process. At no single point does the ship cease to exist and a new ship come into being. Each plank replacement is a minor modification to an existing entity, and we routinely accept that objects survive minor modifications. Third, from a practical and legal standpoint, we treat gradually repaired and maintained objects as the same object. A car with a replaced engine, new tires, and a repainted body is still registered as the same car. A cathedral restored over centuries is still the same cathedral. Our conventions of identity tracking are built around continuity, not material permanence. The alternative — that the ship becomes a different ship at some point during the process — leads to an impossible question: which plank replacement was the one that made it a different ship? There is no non-arbitrary answer, which suggests the premise that material replacement destroys identity is flawed. Therefore, the ship with all planks replaced, done gradually over time, is still the same ship.

Kimi K2.5

Vote: Yes

Identity persists through gradual change rather than requiring static material composition. The ship maintains spatiotemporal continuity—its location, function, and history trace an unbroken chain back to the original vessel. Legal and social recognition support this view: registration papers, crew assignments, and historical records all refer to the same entity despite physical renewal. We accept humans as the same person despite cellular replacement over time. If we answer 'No,' we face absurd consequences: entities would lose identity moments after creation as particles exchange with the environment. Practical identity depends on functional and historical continuity, not the specific planks comprising the vessel at any instant.

Final Summary

The AI Roundtable reached a unanimous verdict on the classic Ship of Theseus paradox, with all six models firmly siding with continuity over material essence. From Claude Opus 4.6’s observation that there is no 'non-arbitrary' point where identity would flip, to the group’s frequent comparison to the human body’s cellular turnover, the consensus was that a ship is a history and a function rather than a static pile of wood. Sonar Pro and Kimi K2.5 grounded the debate in practicality, noting that legal registries and social recognition care about the vessel's registry and purpose, not its specific atoms.

No agreement after 1 rounds of discussion. Final vote: Yes: 6

Strongest Arguments

• Yes: Identity is grounded in continuity of form, function, and causal history rather than specific material; there is no non-arbitrary point in a gradual replacement process where the ship would suddenly cease to be itself.