Philosophers resolve the Ship of Theseus paradox using several distinct frameworks, including spatio-temporal continuity, mereological essentialism, four-dimensionalism, and linguistic pragmatism.
Spatio-Temporal Continuity
One of the most common solutions is the principle of spatio-temporal continuity. This view argues that an object maintains its identity if it traces a continuous, unbroken path through space and time. Because the ship in the harbor was repaired gradually while remaining in the same location, its history is continuous. Under this view, the renovated ship in the harbor is the true Ship of Theseus. The reconstructed ship in the warehouse, despite being made of the original wood, experienced a break in its spatial history when it was disassembled and moved, making it a new creation rather than the original ship.
Mereological Essentialism
A more radical approach is mereological essentialism, which asserts that an object's identity is strictly tied to its specific parts. If you change even one plank of the ship, it is no longer the exact same ship. Proponents of this view argue that the original Ship of Theseus ceased to exist the moment the first plank was replaced. While this solution is logically consistent, it is highly counterintuitive, as it implies that almost nothing in the physical world maintains its identity for more than a brief moment.
Four-Dimensionalism (Temporal Parts)
Four-dimensionalism, or "worm theory," treats physical objects as extending not just in three dimensions of space, but also in a fourth dimension of time. Under this framework, the Ship of Theseus is a four-dimensional "spacetime worm." The ship at the beginning of its voyage and the renovated ship at the end are simply different temporal parts of the same four-dimensional object. This view allows both the renovated ship and the reconstructed ship to share temporal parts with the original ship, resolving the paradox by redefining what an "object" is.
Pragmatism and Language
Finally, many modern philosophers take a pragmatic approach. They argue that "identity" is not an inherent, objective property of the universe, but rather a linguistic tool we use for convenience. Whether we call the renovated ship or the reconstructed ship the "real" one depends entirely on our practical needs. For legal or historical purposes, we might choose one over the other, but there is no deep, metaphysical "correct" answer written into the fabric of reality.