Identity

What is identity?

Identity is one of the most important first principles of life. A clear understanding of the abstract concept of identity forms the basis of a lot more complex and concrete observations that we will discuss later on. For the sake of brevity, let’s consider things and beings as entities. In a philosophical sense, identity is a relation each entity bears only to itself. In a sociological sense, it is a set of idiosyncratic attributes that make an entity unique. There is not much of a difference between the two. Either way, it is the fact of being the same as itself.

In this article, we are concerned with the strict notion of numerical identity which is different from the qualitative identity associated with the terms like ‘identical’ or ‘same’ in ordinary language that are used to refer to the relation between two entities that have common attributes.

Identity and persistence

Is an apple today the same as the apple tomorrow? If an entity is the same as itself, does it need to be the same across time? Other things remaining constant, the dimension of time still changes. Despite the changes in time, entities retain their identity. That means identity persists through time. In fact, the persistence of identity makes the concept of identity more complex. That brings us to the most important question – Under what conditions does an entity persist through time as one and the same entity?

Composition as Identity

Composition is the relation between a complex entity and the parts it is made up of. One can argue that the apple today is made of the same components that it was made of yesterday and hence it is the same apple. An entity is often considered nothing over and above its parts. But is the identity of an entity really defined by what it is composed of?

Though some changes are not apparent, biologically and chemically, the apple has undergone changes. In a changing world, entities undergo constant changes. Despite the changes in composition, those entities retain their identity. That means identity persists through changes in some of the compositions.

Take humans for example. We have a sense of being a continuous and persistent self. But our bodies are continuously replenishing their cells. Red blood cells live for about four months, while white blood cells live on average more than a year. Skin cells live for about two or three weeks. Colon cells live for about four days while brain cells typically last an entire lifetime. At any given point in time, we are made up of different component parts from the ones we were previously made up of. Yet, it doesn’t change our identity.

The Paradox of Identity

So what does it mean for an entity to be the same if it changes over time? If all the parts of an entity are replaced over time as in the popular paradox of the Ship of Theseus, in what way is it the same?

Say, for example, you got a bicycle (A) as a gift from your grandfather. With regular usage and natural wear and tear, you replace one of its parts with a new one. So is the bicycle that you have now, still the same bicycle gifted by your grandfather? Despite the changes in composition, entities retain their identity. So, yes, it is the same.

Over time, you continue replacing each part one by one as and when it wears off. Eventually, the bicycle you have now (B), does not have a single part left of the original bicycle (A). So is it still the same bicycle gifted by your grandfather (A == B)? As per the above logic, yes, it is still the same.

Now let’s say your neighbour collects all the discarded parts and uses them to build a bicycle of his own. He ends up building a bicycle (C) composed of precisely the parts that composed the original bicycle (A). Now, which is the bicycle gifted by your grandfather? Is (A == B) or (A == C)? Since all the parts of C are the parts of A, one can argue that A == C.

By saying A == B and that B != C, it must also be true that A != C. Yet every part of A is a part of C, and every part of C is a part of A. So A and C are two different bicycles even though their parts are the same. A and B have no parts in common, and yet A and B are the same bicycles.

Spatio-temporal Continuity as Identity

So what does it mean for an entity to be the same as itself despite changes in composition? For an entity to persist, it must trace a continuous path through space-time. And tracing a continuous path allows change of parts, as long as the change is gradual and the form or shape of the entity is preserved through the changes of its parts. This brings a new concept into the picture – Perception. But that sounds like a magical answer to solve the above paradox.

But let’s say, in the above example, instead of replacing all the parts of the bicycle (A), you disassembled all the parts and stored them in separate boxes. After a few days, you took them out and reassembled the bicycle (B) with the very same parts. However, there is no continuously existing bicycle-shaped object tracing a smooth path through space-time. Is A == B? The reassembled bicycle (B) is made of exactly the same parts as the one (A) that was taken apart, and hence it is the same bicycle.

So what does it mean for an entity to be the same?