As Edgar Spence implied with his question, it really comes down to how we define nature. For me, nature is *phusis, *the process by which one thing follows another with such robust regularity that we can derive wondrous things like the laws of physics from observing it. Nature in this sense corresponds to the causal; all that happens under the force of necessity (ananke). From there, I describe as "supernatural" anything that happens gratuitously, without necessity, out of a radical freedom that is not reducible to any natural process.
When an elderly man thanks a young woman for giving him her seat on the bus, he is acknowledging, by this "thank you," a supernatural event -- something which no law of physics (or psychology) necessitated, something that happened through a kind of irruption of grace (i.e. the supernatural) in the world. In other words, the supernatural is the acausal. It is that which escapes -- radically transcends -- the system of eternal debt implicit in the machinery of an absolute causation. As I've said in previous courses, the creative imagination is supernatural because it involves a causal leap out of phusis and into the realm of the possible (the imaginal). Indeed, ultimately, even nature has a supernatural basis, since causation cannot have a causal foundation. Seeing this moves nature out of the realm of debt and turns it into pure gift.