The philosophy of self defines, among other things, the conditions of identity that make one subject of experience distinct from all others. Contemporary discussions on the nature of the self are not thereby discussions on the nature of personhood, or personal identity. The self is sometimes understood as a unified being essentially connected to consciousness, awareness, and agency (or, at least, with the faculty of rational choice). Various theories on the metaphysical nature of the self have been proposed. Among them, the metaphysical nature of the self has been proposed to be that of an immaterial substance.