"Soul" is a word-concept. I think it is important to have in our language, even though I don't think it necessarily refers to anything real and definable. I'm interested in the variety of meanings people ascribe to it, and assume those have some value or significance.
To make an analogy, soul is to the human being as dark matter is to astrophysics -- an admission that there's something out there but we don't know what is its. A placeholder for the unknown, or maybe even the unknowable. Without that placeholder, human imagination would complacently assume all is known and definable, which is not the case.
I reviewed the large variety of ideas associated with the word Soul, at http://en.wikipedia.org/wiki/Soul. Here are a few passages from that article that stood out for me.
"Unlike Plato and the medieval religious tradition, Aristotle did not consider the soul to be a separate, immortal occupant of the body, just as the act of cutting does not occur without a knife or axe, the soul ceases to exist at the death of the body. In his view, the soul is the actuality of a living body."
"Summarizing Hillman's views, author and psychotherapist Thomas Moore associates spirit with "afterlife, cosmic issues, idealistic values and hopes, and universal truths", while placing soul "in the thick of things: in the repressed, in the shadow, in the messes of life, in illness, and in the pain and confusion of love."[15] Hillman believes that religion—especially monotheism and monastic faiths—and humanistic psychology have tended to the spirit, often at the unfortunate expense of soul.[5] This happens, Moore says, because to transcend the 'lowly conditions of the soul ... is to lose touch with the soul, and a split-off spirituality, with no influence from the soul, readily falls into extremes of literalism and destructive fanaticism.' "
"Science and medicine seek naturalistic accounts of the observable natural world. This stance is known as methodological naturalism.[80] Much of the scientific study relating to the soul has involved investigating the soul as an object of human belief, or as a concept that shapes cognition and an understanding of the world, rather than as an entity in and of itself.
When modern scientists speak of the soul outside of this cultural and psychological context, they generally treat soul as a poetic synonym for mind."