From my understanding, the unity of spirit, soul, and body is considered to be a ὑπόστασις, or "person." But, what argument is there against the soul itself (apart from the body) being a ὑπόστασις? It seems the soul possesses reason. It exists by itself. So, why is it not considered to be a ὑπόστασις? Or, if it is considered to be a ὑπόστασις, by who and where is such an argument affirmed?
NOTE: To clarify, I mean, ὑπόστασις as an equivalent to Greek πρόσωπον and Latin persona as understood in Trinitarian creeds and theology.