Q. In teaching catechetics, I have been told that I shouldn’t use the phrase that a human being is "a soul plus a body." What is wrong about this? Isn’t it in fact a correct description?
A. The issue at stake here is quite profound, one which no less a genius than St. Thomas Aquinas was able to comprehend and explain. And despite his university lectures on the topic, he was actually heckled in class. That his explanation was absolutely correct, if also extremely profound, has been seconded by the Church in its explanation of the body-soul relation.
From the pages of Sacred Scripture and by applying reason illumined by Revelation, it becomes quite clear that the human being is a unit: soul expressed by body. The great German theologian, Romano Guardini, who was on the threshold of so many of the new insights in expressing Catholic doctrine just prior to Vatican Council II, described the human being as "spirit expressed and made active through the body."
But it was the 13th-century Thomas Aquinas who helped theology the most toward a reasonable explanation of the body-soul relationship. Etienne Gilson, one of the modern world’s most respected interpreters of Aquinas, once put it this way:
"… the soul … shares its being with the body; more precisely, it receives the body in the communion of its own act of being…. There is only one single act of being, that of the soul for the whole individual human substance, including the form, the matter, and all the individuation…."
Thus, the human soul is not simply a spiritual substance making use of a body, not simply a substance which can, by virtue of its being immaterial, service the body and live a life of its own, as it were…."
Plato, the mentor of Aristotle, and one of the most creative minds ever (d. 347 B.C.), explained the body-soul relationship roughly in terms of a pilot within a ship. Aristotle was the philosopher who gave us the more realistic explanation, the one which Aquinas built upon.
Hence, Thomistic philosophy and theology rule out any Platonic or Neo-Platonic approach to the body-soul unity . The human soul is not merely a spiritual substance making use of a body.
To cite Gilson again: "… it is true that men are individualized by their bodies, but the human body truly deserves to be called such only while the soul animates and imparts life into it; it is a body because the soul actually confers upon it the being it possesses."
Gilson went on to argue that man could not possibly have a body if he did not have an intellect – just as he could not have an intellect if he lacked a body. "In such an intimate union," he added, "neither of the integral parts can be conceived without the other, but it is the intellect, not the body, that gives to the whole its actual existence, its very being."