Ship of Theseus: Identity Over Time

Refit the Hull

Replacement speed 2.0 / s

Criterion of Identity

Ship A has never stopped existing in one place — by spatiotemporal continuity, it is still the same ship.

Live State

Planks replaced

0 / 40

Ship A original matter

100%

Ship B reassembled (from originals)

How it works

The Ship of Theseus (Plutarch) asks: if every plank of a ship is replaced one at a time while it stays seaworthy, is the finished ship still numerically identical to the one that set sail? Thomas Hobbes sharpened the puzzle by imagining the discarded planks collected and reassembled into a second ship — leaving two candidates with equally plausible claims.

This simulator makes both ships literal. Ship A keeps its shape and location the whole time; every plank you replace is removed from A and appears, unchanged, in the matching slot of Ship B behind it. Three real metaphysical criteria disagree about which one is "the" original:

Spatiotemporal continuity: identity tracks a continuous
  causal/spatial path through time — A wins, always.

Material composition:      identity tracks which object
  holds the majority of the original matter — the
  verdict flips once more than half the planks move.

No-fact-of-the-matter:     (Parfit) once every physical
  and causal fact is fixed, "which one is really it" is
  an empty further question — both are equally coherent.

Replace Next Plank / Auto-replace — moves one plank at a time from A into B, in a randomized order fixed at each reset.
Criterion buttons — switch which philosophical rule the verdict panel applies to the current state.
Readouts — % original matter left in A and % of B rebuilt are two faces of the same number, tracking the material-continuity criterion directly.

The same structure underlies debates about personal identity over time (do you survive total cellular turnover?), corporate identity, and the four-dimensionalist "perdurantism vs. endurantism" split in analytic metaphysics.

Original plank New plank

⚠ Couldn't load the 3D engineThree.js failed to load from the CDN. Check your connection and reload.

Ship of Theseus: Does Identity Survive Total Replacement?