Consciousness and Personal IdentityIn recent philosophical discussion, this problem is often motivated by way of an example
introduced by Derek Parfit (1984: 199–200). Suppose in the future we are offered the opportu-
nity to travel off-world to the moon or to Mars by way of teleportation. Rather than spending
years cooped up on a space shuttle, one could simply step onto a teleporter pad, press a button,
and wake up on Mars. How does the teleporter work? It scans the traveler, records her mental
and physical “pattern,” destroys the traveler’s body on Earth and then imposes that mental and
physical pattern on new matter on Mars. The person now on Mars has a new body – the old
one was destroyed – but has a continuity of consciousness with the person who stepped onto
the teleporter pad on Earth.
Given just what we’ve said so far, the teleporter example may well seem to support the con-
tinuity of consciousness view. Insofar as we’re inclined to view such a procedure as a form of
transportation rather than a means of suicide, the case provides us with another case where our
intuitions favor continuity of consciousness over sameness of body. (Though the body on Mars
may be qualitatively identical to the body on Earth, i.e., while it might look exactly the same as
the Earth body, it is not numerically identical to the body on Earth.) But Parfit adds an additional
wrinkle that calls those intuitions into doubt: What if the teleporter neglected to destroy the
body on Earth? Though it still scans the mental and physical pattern and imposes it on new
matter on Mars, suppose that it leaves completely intact the body that steps onto the trans-
porter. With this added wrinkle, it no longer seems clear that the person on Mars is the same
person as the one who stepped onto the transporter – despite the continuity of consciousness
between them.
So how should we assess this case? There seem to be four options: (1) The traveler exists on
Earth and not on Mars; (2) she exists on Mars and not on Earth; (3) she exists in both places;
or (4) she exists in neither place. For someone who subscribes to the continuity of conscious-
ness view, there seem to be problems with all four of these options. To make the case easier to
talk about, let’s refer to the person who stepped on the transporter as Initial-Traveler and to the
two resulting persons as Earth-Traveler and Mars-Traveler. Earth-Traveler and Mars-Traveler do
not share consciousness with one another, but at the moment Mars-Traveler comes into exist-
ence, her consciousness is continuous with Initial-Traveler in exactly the same way that Earth-
Traveler’s consciousness is continuous with Initial-Traveler. Because of this, there is no reason
to privilege one of the first two options over the other, and they thus must both be discarded.
Might we instead choose option (3) and claim that the traveler exists in both places? Though
this may initially appear to be an appealing option, recall that identity is a transitive relation: if
a is identical to b and b is identical to c, then a is identical to c. So if we say that Initial-Traveler
is identical to Earth-Traveler and we say that Initial-Traveler is identical to Mars-Traveler, then
it follows that Earth-Traveler is identical to Mars-Traveler. But this seems wrong – after all,
as we’ve just noted, Earth-Traveler and Mars-Traveler do not share consciousness with one
another. Thus, our third option seems just as problematic as the first two.
What about the last remaining option, the claim that the traveler exists in neither place, i.e.,
that the traveler ceases to exist. From the perspective of the individual on Earth, this conclu-
sion would no doubt seem absurd. How could stepping onto a teleporter pad and being (non-
destructively) scanned make you go out of existence? The conclusion seems equally absurd from
the perspective of the individual on Mars. The relationship between Mars-Traveler and Initial-
Traveler in this case seems just like the relationship between Mars-Traveler and Initial-Traveler
in the case as first introduced, before the added wrinkle of reduplication. In both cases there is
continuity of consciousness between them. If this continuity is good enough for Mars-Traveler
to be the same person as Initial-Traveler in the case as first introduced, then why shouldn’t this
continuity be good enough for Mars-Traveler to be the same person as Initial-Traveler in the