on permanent public display. However, the timber eventually
begins to rot and over the years carpenters replace planks one
by one. At what point does the ship cease to be the original ship?
Finally all the old parts of the original ship have been replaced
by new parts. If every plank, rib, and panel, along with the nails
that held them together, has now been replaced, how can it be
the same ship? Surely it is only a replica?
We know that the constituent cells of our bodies are simi-
larly continually dying and being replaced. We change in many
other ways too; what makes us the same person as we move
through time? In the absence of an adequate or persuasive
answer, many philosophers have denied that we have an
unchanging essence that makes us who we are.
Because of this inability to define ‘identity’ in philosophy, the
concept has become something of a hydra (to borrow from Greek
legend again!). In their article ‘Beyond “Identity”’ in Theory and
Society Vol. 29 (2000), Professor of Sociology Rogers Brubaker
and historian Frederick Cooper acknowledge that the word can
be understood in many ways and in many different forms,
depending on “the context of its use and the theoretical tradi-
tion from which the use in question derives.” Furthermore, theseI
s it possible to bring science into philosophy? There is one
outstanding example in which the answer is without doubt
yes. It relates to notions of personal identity.
When philosophers grapple with the issue of what consti-
tutes personal identity that endures through time they gener-
ally rely on description rather than definition. In fact, the
humanities have failed to define ‘identity’ concisely. The Oxford
English Dictionary defines ‘identity’ to mean: “The sameness of
a person or thing at all times or in all circumstances; the con-
dition or fact that a person or thing is itself and not something
else.” Unfortunately, philosophy has been dogged by its inabil-
ity to explain what can be meant by ‘sameness’ for something
that changes. As a result, it has not been possible to apply the
dictionary definition.
One of the problems with the concept of identity can be
traced to the age-old question about the conditions under which
something persists as the same object through time. But this
idea contains the key to understanding how science can con-
tribute to solving the dilemma. The paradox is succinctly illus-
trated in the famous Ship of Theseus thought experiment.
Greek hero Theseus sails home to Athens and his ship is put16 Philosophy Now ●^ August/September 2019DNA & The Identity Crisis
Raymond Keogh has a science-based take on personal identity.
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