To understand Locke’s concept of personal identity it is necessary to understand what he means by identity and what he means specifically by personal identity. Locke states there are three substances that we have ideas of and that have identities. He defines idea in Essay concerning Human Understanding as “whatsoever is the object of the understanding when a man thinks” (Essay, chapter 1, section 8). That is to say that an idea, to Locke, is the basic unit of human thought. Identity is based off of comparison of these ideas in different times and places.
Locke first splits substances of which we have ideas into three groups: God, finite intelligences, and bodies. Locke writes that identity is ascertained by a comparison between the idea of an object at one moment in one place, and the idea of the object at another time and place. If these two ideas match up, that is to say that they are exactly the same, then the object itself is the same. God’s identity is indubitable, as he is eternal and unchanging. Finite intelligences and Bodies each have an exact beginning, and when you compare the current finite intelligence or body to its beginning you can understand its identity ( Essay,II,2). An object cannot have two distinct beginnings in time and space, and two objects cannot share in one beginning. As such, finite intelligences and bodies each have unique beginnings which identify them. Locke’s idea of personal identity is based on the same principal of continued comparison as the identities of the three substances.
Personal identity or the identity of self is defined as the conditions under which a person can be considered to be the same at two different times. Locke bases personal identity squarely on consciousness. He defines consciousness as the perception of what passes in a man’s own mind. That is to say that, to Locke, consciousness is sensing that you are sensing or thinking, or being aware of the processes of your own mind. Consciousness alone defines personal identity. Without being cognizant of the sensations and ideas that pass through one’s own mind, there can be no idea of self. Without sensing that I am sensing, there is no certainty that I are not a simple observer. The experience would be akin to watching a movie shot through someone else’s eyes. I can see what they see, but certainly cannot sense that I am seeing these objects myself. I would be under no illusions that the video was my own experience. I would be a step removed, and the experience would not be my own.
The substances of body and soul do not play a part in personal identity. After all, a body can change while a person stays the same. Someone can lose an arm or get taller, and still be considered the same person. This is because of the continuity of the consciousness. If personal identity were based in the substance or form of the body we would constantly be changing identity as we grow. And if it were based on the substance of soul, someone claiming to be a...