Consider the sentence: "I sweat."
Who is this I that I refer to? Do I choose to sweat? No. I sweat involuntarily. And yet it's perfectly natural to say "I sweat" or "I digested my food" or "I was breathing hard after the run." But I did not do these things because of a choice I made, but because of bodily processes. So we use "I" to refer to something that does not choose. In fact, I can sweat, digest food, and breathe even while unconscious. So we can use "I" to refer to something that is unconscious.
Yet we also use "I" to refer to that which consciously experiences and chooses.
Our bodies are so strongly associated with us that we use "I" and "You" statements to refer to them.
I don't sweat, my body does. I don't digest food, my body does. I don't breathe, my body does.
Who is this "I" that doesn't do these things? It is the I of self, mind, soul, consciousness, subjectivity, choice, experience. So we have two senses of I, an embodied sense and an unembodied sense. There are three possible options:
The essential I is the embodied sense.
The essential I is the unembodied sense.
The essential I is a whole made up of both the embodied and unembodied senses.
Another option is that there is no essential I, as the self is empty or an illusion or non-existent. But I take that kind of view to be self-evidently false.
I go for option 2: the essential I is the unembodied I that experiences and chooses. All embodied "I" statements can be paraphrased as "my body" statements.
One reason why I go for this option is because it seems to me that one of the most essential aspects of what it means to be me involves the pain and happiness I experience, especially the pain. Jordan Peterson once said that nothing is more real than pain.
My body might facilitate the experience of pain, but my body is never in pain. I am the one who has to be in pain. Whatever that thing is that is in pain, that first-person, subjective, self-aware, singular, unified, thinking, feeling, remembering, choosing, introspecting, metacognizing, experiencing thing, that is the soul, the self, the mind, the person, and that is what I am.
We can make distinctions between these terms. Perhaps person refers strictly to the essential property of being a particular subject, while mind refers to both the personhood as well as the non-essential mental properties associated with that particular person, including mental properties like memory and subconsciousness.
"Haecceity" refers to the suchness of something, or the particularity of it. My haecceity is that which differentiates me from things that are not me. So to make sense of my haecceity, we first need to make sense of my essence. What does it mean to be me? It means to be a very particular subject. And so the suchness of one subject (person) is what differentiates the suchness of another subject (person). And so when it comes to persons, the essence and the haecceity are the same, but both answer different questions, with the first answering the question of what it means to be that thing, and the second answering the question of what it is that differentiates this thing from other things.
Essence and haecceity usually do not overlap. For example, the essence of my vacuum cleaner probably involves its function (both actual and modal -- a broken vacuum is still a vacuum) and history. Maybe its appearance as well. But there are many other properties associated with my vacuum, like its age, size, location, and so forth. These properties help distinguish it from other objects. Together, these differentiating properties form the haecceity of the vacuum. So a haecceity is a property or bundle of properties that differentiates one object from another.
Question: negative space properties. Is differentness between two things a property? It can't be a universal because a particular differentness might lack multiple realizability. But it's not a property, as it's the negative space between two properties. It's a lack of two properties, but shaped by the two properties. So what is differentness exactly?