WARNING: The following contains spoilers for WandaVision Episode 9, "Series Finale," streaming now on Disney+.
When faced with a homicidal A.I. bent on destruction and mayhem, one of the time-honored solutions is to present it with a logical paradox. From Captain Kirk to John Connor, many a sci-fi hero has averted catastrophe by overloading a robot in such a fashion. This sort of attack works by capitalizing on an artificial intelligence's overreliance on logic. Take, for example, the phrase "this statement is false." When followed purely logically, the binary question of if that statement is, in fact, false is impossible to answer. A computer devoting all of its intelligence to solving it won't get anywhere, no matter how much or how quickly it thinks.
The latest episode of WandaVision invokes the same trope, as Vision finds himself in a face-off against his own reconstituted corpse. Brought back online by S.W.O.R.D. Director Tyler Hayward, this pale Vision was reprogrammed with a single directive: to kill the "true Vision." Finding he can't defeat his previous body by force of arms, Vision instead tries to defeat it through a similar chain of logic as Kirk and Connor before him. But instead of overloading his opponent's processor, Vision tries to undermine its new programming, and to do this, he poses to the pale Vision a philosophical conundrum based on the old parable of the Ship of Theseus.
The Ship of Theseus was first posed in its current form by Greek philosopher Plutarch, who asked what would happen if the planks of a ship were replaced over time. No part of the ship remains the same once every piece has been replaced, but the gradual process in which it was changed poses the question of at what point it stops being the same entity. Vision also invokes a further corollary posed by English thinker Thomas Hobbes, who asked what would happen if the old planks of the ship were used to build a second vessel.
Instead of being a strict abstract, the philosophical problem has a rather practical use as it applies to the two forms of the hero. Vision himself represents the first version of the problem. Wanda generated him from nothing, but he is seemingly-identical to how he was before being killed by Thanos. In making this argument, he convinces the resurrected Vision that he is not the "true Vision." While he is more like the previous incarnation of Vision than his pale counterpart, he is a perfect recreation of the original. This is good enough for Wanda but is not the same as being the original android.
In contrast, the pale Vision represents the second version of the Ship of Theseus. All of the planks of the ship (or in this case. the pieces of Vision) have been gathered and reassembled by Hayward and S.W.O.R.D., perfectly reconstructed and missing only the Mind Stone. That spark of life is replaced by a fragment of Wanda's magic, extracted from the drone she shot down inside the Hex. And because of that substitution, the resurrected Vision understands that he still cannot be considered the "true Vision."
The final coup de gras in Vision's argument is his answer to the Ship of Theseus: "Perhaps the rot is the memories, the wear and tear of the voyages. The wood touched, by Theseus himself." What makes the Ship of Theseus its true self are the voyages it has undergone, the individual grooves that etch themself into its surface. The pale Vision is lacking these memories, locked away by Hayward in order to create a perfect weapon. When Vision restores them, his doppelganger realizes that he is the "true Vision," possessing both the material and memories of his original self. He flies off and isn't seen again for the rest of the episode, defeated -- but also freed.
Written by Jac Schaeffer and directed by Matt Shakman, WandaVision stars Elizabeth Olsen as Wanda Maximoff/Scarlet Witch, Paul Bettany as Vision, Randall Park as Agent Jimmy Woo, Kat Dennings as Darcy Lewis, Teyonah Parris as Monica Rambeau and Kathryn Hahn as Agnes. All episodes are now available on Disney+.