The problem is, it will always fall back to defining what a soul actually is. Any which way you cut it, the idea of a soul is linked to a belief, whether it be dogmatic or a philosophy. Since each group is divided into many subgroups, the whole acknowledgement of a soul and what it means to the individual, the circumstances surrounding it's existance varies so greatly, it would be impossible to find a correct definition of a soul. Like Salty said, the topic resides beyond the the operable limits of science.