Philosophy of self

Philosophy of self examines the idea of the self at a conceptual level. Many different ideas on what constitutes self have been proposed, including the self being an activity, the self being independent of the senses, the bundle theory of the self, the self as a narrative center of gravity, and the self as a linguistic or social construct rather than a physical entity. The self (or its non-existence) is also an important concept in Eastern philosophy, including Buddhist philosophy.

Most philosophical definitions of self—per Descartes, Locke, Hume, and William James—are expressed in the first person. A third person definition does not refer to specific mental qualia but instead strives for objectivity and operationalism.^{[citation needed]}

To another person, the way an individual behaves and speaks reflects their true inner self and can be used to gain insight into who they really are. Therefore, the intentions of another individual can only be inferred from something that emanates from that individual. The particular characteristics of the self determine its identity.^{[citation needed]}

Aristotle, following Plato, defined the psyche as the core essence of a living being, and while claiming that it did not exist apart from the body, he considered its so-called "intellect" part to be immortal and perpetual, in contrast to its organism-dependent vegetative/nutritive and perceptual functions. In his theory of causes and of act and potency, Aristotle emphasizes beings in relation to their actual manifestation, and in turn the soul was also defined by its actual effects. For instance, if a knife had a soul, the act of cutting would be that soul, because 'cutting' is part of the essence of what it is to be a knife. More precisely, the soul is the "first activity" of a living body. This is a state, or a potential for actual, or 'second', activity. "The axe has an edge for cutting" was, for Aristotle, analogous to "humans have bodies for rational activity," and the potential for rational activity thus constituted the essence of a human soul. He states: "Soul is an actuality or formulable essence of something that possesses a potentiality of being besouled", and also "When mind is set free from its present conditions it appears as just what it is and nothing more: this alone is immortal and eternal". Aristotle used his concept of the soul in many of his works; his main work on the subject is De Anima (On the Soul).

Aristotle also believed that there were four sections of the soul: the calculative and scientific parts on the rational side used for making decisions, and the desiderative and vegetative parts on the irrational side responsible for identifying our needs. A division of the soul's functions and activities is also found in Plato's tripartite theory. The problem of one in many is also remembered by Aristotle, nonetheless:

If then the soul is of its very nature divisible, what holds it together? Not the body, certainly: much rather the contrary seems to be true, that the soul holds the body together; for when it departs, the body expires and decomposes. If there is some other thing which makes it one, this other is rather the soul. One would then have to ask, concerning this other, whether it be one or of many parts. If it is one, why not call it the soul straightway? But if it is divisible, reason again demands, what it is that holds this together? And so on ad infinitum.

While he was imprisoned in a castle, Avicenna wrote his famous "floating man" thought experiment to demonstrate human self-awareness and the substantiality of the soul. His thought experiment tells its readers to imagine themselves suspended in the air, isolated from all sensations, which includes no sensory contact with even their own bodies. He argues that, in this scenario, one would still have self-consciousness. He thus concludes that the idea of the self is not dependent on any physical thing, and that the soul should not be seen in relative terms, but as a primary given, a substance. This argument was later refined and simplified by René Descartes in epistemic terms when he stated: "I can abstract from the supposition of all external things, but not from the supposition of my own consciousness."

David Hume pointed out that we tend to think that we are the same person we were five years ago. Although we have changed in many respects, the same person appears present as was present then. We might start thinking about which features can be changed without changing the underlying self. Hume, however, denies that there is a distinction between the various features of a person and the mysterious self that supposedly bears those features. When we start introspecting, "we are never intimately conscious of anything but a particular perception; man is a bundle or collection of different perceptions which succeed one another with an inconceivable rapidity and are in perpetual flux and movement".