Is it biology? The ephemeral particles that you are made up of? An instinctive drive embedded in human nature? The fruits of evolution drawing illusions of freewill?
Is it anatomy? The current of billions of neurons and cells rippling into emergent properties? How effectively you hearts pump blood down spiraling canals, our vision, our diagnoses, our allergies, and disabilities?
Is it beauty? The symmetry of your bone structure, the azure of your eyes? How identically your appearance molds to the ideal?
Is is nurture? Socio-economic class, the education of your parents, your privilege, your cultural and ancestral values? Is it how many times your parents tucked you in reminding you they loved you? Is it boiling soup catered to you on sick days or an unrelenting emptiness screaming your family does not care?
Or is it something ethereal? Something with no name? Something deep inside of us, yet nowhere at all, something invisible and powerful and something that is nothing and everything all at once?
These are the questions that arise when I consider philosophical thought experiments of identity. What is the defining characteristic or condition of identity, of character, or a human being? Can any object ever be concretely and statically defined, and if so, what allows an object to be fundamentally the same object?
First I consider Theseus's Ship paradox: imagine there is a ship. This ship goes on a journey, and when it returns, the wooden plank must be replaced; so it is. Year by year, as the ship goes on more and more journeys, more parts of the ship are replaced until eventually every part of the ship is replaced. The ship still appears exactly the same, but no component that composes the ship is from the original Theseus's Ship; but, it it still Theseus's Ship, or a whole new entity?
Justifiably, answering the question regarding an inanimate variable is far easier. Although its parts have been replaced, it is still Theseus's ship because the parts have replaced identically to the first ship. Thus the ship's intrinsic value lies in its spirit--a factor which has remained constant.
Next, I imagine if Theseus's ship would still be Theseus's ship if each part was replaced and refurbished with newer, modernized parts. The original ship was made mainly of mahogany, wooden, scented, and providing a feeling of warmth and nature. Yet, as the ship is replaced piece by piece, the wood planks become steel, and years later the ship is unrecognizable. For most, we would immediately consider it a different ship. Would this imply that appearance is the paramount factor of identity? I simply think it insinuates that since value lies in the idea of something, rather than the thing itself, that appearance easily changes ideas. I apply this to human beings and find the law coherent. Often an impression of a person correlates mostly to their physical appearance.
Theseus's Ship is a clear metaphor not for naval architects but for the growth and development of human identity. Through our lives, we do not remain stagnant characters. Our looks change, our values, our minds, our knowledge, our interests, our feelings, our physical selves, our characteristics, and the way others perceive us. Yet, one would still consider 54 year old Kit Harrington to be the same person as 23 year old Kit Harrington. Perhaps the ship is not truly analogous to the human experience. Besides, not all parts of us are replaced; our DNA replicates, and parts of us remain throughout the courses of our lives. Furthermore, unlike the ship, our identity changes following a far more gradual course. And as we change and grow each second of each day, our memories draw a line connecting everything we ever have been with everything we are identifying our identity. Thinking of memory I am immediately drawn to a Tom Stoppard quote: “We cross our bridges when we come to them and burn them behind us, with nothing to show for our progress except a memory of the smell of smoke, and a presumption that once our eyes watered.” Perhaps, memory and therefore the mind is what makes us, us. For objects it is the idea that defines it, and for human beings, it is the mind.
This is complicated by neurological diseases and disorders then, but I suppose that is why they are so devastating: they target one's very identity. The concept I introduced also simplifies the next thought experiment I would reference. If you clone a person, is the clone still the same person. If the clone's mind is not the same, if it does not contain all the same memories, and emotions, and breadths of knowledge, then the clone is not the same.