[Update: for a related post, see here]
Here is another topic on which I commented over at The Linde (see this post). It pertains to the big and very significant issue of the relationship between nature and grace. And this issue is a very important backbone to any discussion of how we should understand the virtues, natural and supernatural.
From the point of view of a Catholic understanding of the world, natural and supernatural virtue are closely related and yet very different. Natural virtues can be developed with merely ordinary natural human powers and abilities (e.g. courage, patience, generosity, friendliness). Supernatural virtues have a supernatural goal and can only be developed with the assistance of divine grace (e.g. charity, fortitude, chastity).
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There is a close relationship between natural and supernatural virtues and between the growth of natural and supernatural virtues.
As I studied virtue (natural and supernatural) at the Dominican House in moral theology classes, one of the things that was very intriguing and clarifying to me was learning something about how St. Thomas understands the relationship between these two basic categories of virtue.
An overly simplistic view (and not correct according to St. Thomas)—one that I think is often a default sort of understanding for many Catholics—is that natural virtue gets you to a certain point. Then, supernatural virtue takes over and from that point on it is supernature “building” upon nature (i.e. “grace building upon nature”). Sort of like laying bricks to construct a wall. The first ten rows, say, are brown, and represent natural virtue. Then, rows 11 and higher are red, and represent supernatural virtue. The latter continues building upward, taking up where the other left off. Or, like a relay race where one racer (natural virtue) hands off the baton to the next racer (supernatural virtue). The transition from one to the other is such that there is a clean demarcation line in between—a nice, neat borderline between them. One shifts to the other in a way that you can point to it and say, “there is where one ended and the other began.”
Wrong—according to Aquinas. This is not how it really works. Grace comes in and infuses, permeates, transforms, what is already there in natural virtue. They continue on together, intertwined and enmeshed one into the other. One Dominican professor liked to use the analogy of food coloring. You have a container of water. Then you add a single drop of coloring (i.e. grace). The water does not become something else. Yet, it is permeated throughout by the color as it spreads through all the water in the container. However, when you look at it, you cannot observe a clean demarcation or break between the water (i.e. nature) and the coloring (i.e. grace). They are completely intermingled once the grace has been introduced and just a little bit of stirring taken place. Now, the grace might be a little or a lot (or gradually more over time). But the point is that the nature and the grace are very closely allied to each other and ought not be thought of in a compartmentalized way.
The amount of water might be analogous to the amount of natural virtue. The natural and supernatural virtue are closely related, while still being of a totally different nature—yet not clearly distinguishable once they have been brought together.
An example. Let’s take courage (as the natural virtue) and fortitude (as its supernatural complement). Using the water image, say a person has built up one gallon’s worth of courage. Then, he converts, is baptized and becomes a practicing Christian. He now has one gallon of an intimately close mix of courage but now infused with a new color it did not have before—the color of fortitude. The amount of natural virtue effects the operation of the supernatural. The supernatural is not caused by the natural, but it is enabled to work upon a broader field by the larger presence of the natural. If there were one-half gallon of natural courage to start, there would be one-half gallon of fortitude-infused courage after grace came in. Likewise, if there were two gallons at first, and so forth.
The water cannot make itself red. That must be supplied into it from without. But, the more water there is in the pot, the more of it there is to become the new color red when the color is added. And similarly as virtue is increased. A person in grace grows in natural and supernatural virtue in a such a way that they both grow in an intertwined fashion, each being like a stepping stone for the other (but without the natural ever being the origin of the supernatural).
So, it is not accurate to say grace “builds” on nature as though one stops at a certain point and then the other begins. Rather, grace infuses (transforms) nature thoroughly without destroying it or covering it over. (You can still see through colored water; but you see through it in a new way). The nature persists and the amount and character of it remain essential to the way in which the infused, new supernature can be enacted.