Nature is in one way opposed to art, and in another way to chance. Nature is opposed to chance because of its intentional character, that is, because there is a causal connection between what something does and what it is. A falling tree might crush a lily, But the activity isn’t natural- otherwise trees couldn’t fall without killing lilies and lilies would live forever until crushed by trees. There is certainly some causality involved in the process, and there is even a sense of “natural” we can use to describe tress crushing flowers as “natural”, but the crucial point is that no one thinks the activity proceeds from either of the two natures involved, that is, from the proper nature or flowers or trees.
But while a tree doesn’t fall to crush a flower, it also doesn’t fall because its a tree! Things other than trees fall, even though it seems pretty clear that a tree is always concomitant with “that which falls”.
Aristotle took one very good run at explaining what “that which falls” is. He pointed to some evidence that falling things were made of earth (for all solid things seem to be either earthen or they corrupt into soil) and he thought that the earthen parts of things were attracted to earth. Earth wanted to be with earth. So earth was, properly speaking “that which falls”. Modern physics gives similar sorts of explanations for other things- any physics teacher can catch himself saying things like “the hot air is trying to get to the cold air” when he is explaining a thermodynamics problem; or “the negative charge wants to take the shortest path to the positive charge” when he’s explaining a circuit. Earth going to earth is the same idea. It was a theory to explain what “that which falls” was. The theory failed, of course. So now what?
The path of modern physics was to analyze simply the activity of falling- to divide it up into number measurements and observe the relationships between various number-measurements. “That which falls” was not treated of directly, but only through the ordered relationships that obtained between the various number-measurements. This is the sense of the modern project “forgetting about natures”. Bacon and Newton and Compte tended to make this point more forcefully than it needed to be made, and they tended to exaggerate the departure from seeking natures. The relationships we obtain between number measurements are still about some definite nature- it’s not as if we have to imagine that “natural laws” are some kind of ghostly platonic force that looks after the speeds of falling things. Even if one says that the laws are about “appearances” they are still the appearances of some nature- otherwise they are not even appearances.