"The philosophical I is not the man, not the human body or the human soul of which psychology treats, but the metaphysical subject, the limit--not part of the world."
--Ludwig Wittgenstein, Tractatus Logico-Philosophicus
Take Descarte's methodological skepticism and acknowledge that your world is comprised entirely of sensory perceptions (ideas are external to it). Next, recognize that the existence of God--defined as an infinite-eternal being, unmoved mover, or originator, sentient or not--cannot be proven by a priori logic, nor by observation. Causal regression in logic, distinctions between finite and infinite particulars, substances and extensions, monads, and the like are incapable of espousing an understanding of ontology greater than "I am", which is itself not a priori.
The understanding of I, the "I am", is inherently a posteriori: it is dependent on your perceptions and thus empirical. The seemingly metaphysical "space" occupied by your mind is outside of the world (see quote at top), yet ostensibly dependent on it. In light of this, one may suspect that the door is left open for the possibility of immortality of the Mind, as we would not be able to apply laws of this world-reality to it. This is probably false. The mind's constitution is independent of subjectivity. Two things lead me to believe this: (1) a law is present in both the world and pure Mind: time; (2) the world of waking reality (think constant, non-crazy reality) is capable of altering one's capacity to think.
That the condition of the psyche can be affected by worldly things external to the psyche (e.g. instinct, appetitive desires, drugs) without its assent, suggests that its physical constitution (e.g. the brain) is being affected. In a false reality, such as a dream or hallucination, the physical constitution of the thinker would remain unaltered. While the perceptions of someone in a dream-state would be radically different from someone in a waking state, the physical constitution of the mind cannot be affected by actions in those states--thereby one could not get a lobotomy in a dream and properly experience its effects.
(Then again, all of this relies on the assumption that there is a true "objective" world-reality that is experienced by the senses in a waking state and that other world-experiences are products of subjective psychology. The question of subjective versus objective reality is a noumenal and ontological one; its answer is beyond our capacity to observe. The arguments set forth on this subject are merely observational hypotheses for the sake of intellectual curiosity. Their practical application is non-existent, ethically or otherwise.)
