Locke, John. An Essay Concerning Human Understanding. The main idea that Locke wants to convey is that what makes up a person and an individual is consciousness, plus memory, which "can be extended backwards to any past action or thought" (4-5), is a part of personal identity. That does not mean that a person can remember every single little tiny detail of experience. It does mean that whoever has a personal identity can link his conscious experience to the continuity of physical experience.
Locke is trying to explain how the mind and body, or material substance, come together to make up the human experience of being, which is for Locke personal identity. He gets into the question of whether there can be two material substances in the same mental substance, only to reject it. Repeatedly he returns to the assertion that "consciousness alone unites actions (and memory and material experience) into the same person" (7). Consciousness is distinguished from thinking, but in Locke's view thinking, reflection, memory, and intelligence, which are uniquely combined in human beings as opposed to plants and animals, is impossible without consciousness, the source of (so to speak) the experience of experience.
The continuity of consciousness is unique to the individual, which means that one individual cannot inherit or otherwise share another individual's body or consciousness (nobody can be Socrates except Socrates). Nor is there one human consciousness of which all human beings partake. Such ideas are classed as "absurdities" by Locke.
This is a commonsense presentation of the experience of being human. Locke's views do not disprove that memory is elusive or that there are different kinds of consciousness and capacities for consciousness. However, even if the material substance of an individual may change (for example, a man may lose a finger), the individual keeps the same identity because of consciousness. The "particles" that make up...