What's the difference between spirits and souls? I don't even know the Christian answer, though the Bible sorta implies they aren't the same thing.
For the word of God is living and active. Sharper than any double-edged sword, it penetrates even to dividing soul and spirit, joints and marrow; it judges the thoughts and attitudes of the heart.
Unless that's hyperbole, used to illustrate just how freaking sharp the word of God is.
Anyway, the dictionary.com definitions for "soul" and "spirit" are pretty similar: "The animating and vital principle in humans, credited with the faculties of thought, action, and emotion and often conceived as an immaterial entity." The main difference appears to be that spirits can be noncorporeal beings (like ghosts), whereas souls always exist with a body; but that difference doesn't really help distinguish between what is meant by a human's soul and spirit.
Maybe both soul and spirit inhabit the body, but then when the body dies the soul stays attached to to the spirit; that way ghosts fit right into the paradigm. A body without a spirit to animate it becomes a corpse; a spirit without a soul becomes... what? What's a soul without a spirit?
Or maybe souls and spirits are really the same thing? "Soul" is from Old English, and "spirit" is from Old French, which makes me think they're just different words for the same idea.