Artificial as well as natural things come into being as the result of a change and in some sense art is closer to us than nature. After all, we produce artifacts. Well, artisans and artists do, but you and I know what it is like to type a page, make a paper airplane, bake a cake, so perhaps there is a sense in which we are all artists. Man is naturally an artisan; the artificial is natural to us.
A natural thing is made up of matter and form and each of these components is a source of changes we attribute to it. Any natural or physical thing will, if let go of, drop. We attribute this to its matter because a man, his dog, and a geranium will all fall when dropped so we do not think this a peculiarity of humans, dogs, or geraniums. A person's laughter, on the other hand, is thought to belong to her because of the specific kind of thing she is.
Form sets a thing off from other things. This is true of form in its primary sense of shape. You can sort out the square one and the round ones from the rectangular ones. It is because form enables us to sort things that the word for external shape was extended to mean what set one thing off from another in terms of more than its contours. The fact that things can be distinguished by color and place led to calling these features forms too and finally what makes a thing to be a substance of this type rather than that is called its form. Natural kinds or sorts are read from form rather than matter. Nonetheless changes due to the thing's matter as well as those due to its form will be said to be natural to it.
Its nature is that in the thing which is at the bottom of the changes it undergoes and the activities it engages in. It is intrinsic to the thing. Artificial changes, by contrast, come from outside in the sense that they require the intervention of a human being.
When a tree is felled, the wood obtained is a product of nature. Many years ago, an acorn germinated, rain fell, the sun shone, the acorn became the mighty oak that now lies fallen in the forest. Logs, insofar as they are sections of the felled tree made with saw or axe, are artificial things. Lumber is even more so. And the house built from the boards is an even more complicated artifact.
An artifact comes into being when a shape or form is imposed by a human agent on a natural material. So the artifact is composed of matter and form. In the case of logs, the matter is obviously produced by nature. When the logs are the matter from which lumber is made, we are twice removed from nature, the house yet further removed.
An artificial change presupposes a natural matter whether proximately or remotely. No nature, no art.
Remember how Aristotle brought in an example of artificial change in his analysis of physical change. In fact, the primary example of a person learning how to play a musical instrument is a tantalizingly complicated one, somehow blending the natural and artificial. Little Orville learns to play the mouth organ.
Okay. There are natural changes and there are artificial changes. The results of natural changes are physical objects and they are made up of a form and a matter. If the natural change is a substantial one, the result is a substance of which we can say, minimally, that it is composed of prime matter and the form that makes it to be a substance of this kind. The results of artificial changes are artifacts and they too are composed of matter and form, the matter being something natural, the form a shape or distinguishing character imposed by a human being.
If art depends on nature in this way, it also said to imitate nature. What does this mean? Thomas like Aristotle almost always uses the term 'art' to speak of the activity of artisan, not the fine artist. Or to speak of the military art, the art of the master builder, the art of medicine. When he says that art imitates nature, it is of such arts we should first think.
Imitation is one sense means: consciously bringing nature to its goal, aiding nature to fulfill itself. The bandage brings torn flesh together in order that nature might heal it. An art is devised to provide shelter. Nature does not equip the human species with protection against the elements and against enemies. Nature does not prompt the human species to build a habitat in the way in which robins build nests, oven birds build their dwellings, and groundhogs make their burrows.
Instead of this, nature has given man reason and the prehensile hand. That is why art is natural to us. We must fashion what other species are provided. Turtles have shells, birds have nests, foxes have holes, men must make a place to lay their head but no blueprint is given. It can be a cave, a tree-house, a castle in Spain. Art thus provides what nature does not give, though the impulse to be artful is natural to man.
Here are two passages in which Thomas remarks on art imitating nature. The first is taken from his commentary on the Physics (II,I,4,n.171).
The reason art imitates nature is that knowledge is the principle of artistic activity. But all our knowledge is received through the senses from sensible and natural things. Hence our procedure in artificial things is similar to that in natural things. Natural things are imitable by art because the whole of nature is ordered to its end by an intellectual principle, and so the work of nature seems to be a work of intelligence since it proceeds in a determinate way to definite ends -- and that is imitated in artistic activity.
In the preface to his Commentary on the Politics of Aristotle, St. Thomas says this.
Art imitates nature, as the Philosopher teaches in the second book of the Physics The reason for this is that as their principles relate to one another so proportionally do their operations and effects. The principle of art-works is the human intellect, which is derived by a kind of likeness from the divine intellect, which in turn is the principle of all natural things. Necessarily then do artistic operations imitate nature and art-works imitate things that exist in nature. If then one teaching an art produces a work of art, the apprentice desiring to acquire the art should take note so that he can act in a similar way. So it is that the human intellect, which depends on the divine intellect for its intelligible light, must be informed concerning the things it makes looking to things that are naturally produced, so that it may work in like manner.
That is why the Philosopher says that if art were to make the things which exist in nature, it would act in the same way that nature does. But, of course, nature does not completely produce artifacts; it merely provides certain starting points and offers a model. Indeed, art can observe things in nature and use them to complete its own work, although it cannot produce those natural things. From this it is clear that human reason is merely cognitive with respect to things that exist in nature, but in respect to art works it is both cognitive and productive. Hence, human sciences which deal with natural things must be speculative while those which deal with thing produced by man must be practical or operative in a way that imitates nature.
We said earlier that art is an extrinsic principle whereas nature is an intrinsic one. This may seem unhelpful if the point is only that the artisan who makes the art work is other than and extrinsic to it. The same can be said of any effecting cause of a change, natural or artificial.
It is, of course, true that natural changes and thus natural things require effecting causes which are other than and thus extrinsic to them. What is meant by the enigmatic remark is that the natural matter of the art-work does not have within itself a capacity to become the art-work. In natural change, the matter to which the effecting cause brings a new form has a capacity to receive that form. Aristotle made this point by saying that if you planted a wooden art-work, say a bed, and it grew, what would grow would be an oak, say, and not a bed.
The contrast between art and nature, the artificial and the natural, is here meant only to cast a little more light on what is meant by the natural or physical. To know how something differs from something else is to know it better, to be able to discriminate. The contrast is not, as we have been suggesting, between two wholly unrelated realms. Rather the realm of art is said to be in various ways piggy-back on nature. The ultimate source of this is that the universe as a whole is something God has made, is an art-work of God, and this provides a vast analogy to those human incursions into the natural world whereby we reshape and fashion it for purposes of our own. That it is natural for us to do this does not mean that the artful shapes natural material takes on are natural to it, as if computers and BVD's and popsicles would show up without human ingenuity and inventiveness.
Nowadays we are very alive to the extent to which we can safely go in our technological interventions. The sense of natural limits to art is suggestive of a moral boundary. But more of that later when we speak of natural law in the moral sense.
I reply that art should be called nothing else than right reason about things to be made. Their good does not consist in any disposition of the human will but rather that the work that comes to be is good in itself. The artist is not praised as an artist because of the will with which he works but because of the quality of what he makes.
Art then is properly an operative habit. Nonetheless it has things in common with speculative habits because in the latter too what counts is the things they consider rather than the way will relates to them. So long as the geometer demonstrates the true, the condition of his appetitive part -- whether he is happy or sad -- is irrelevant, as it is with the artist, as was mentioned. Art has the note of virtue, then, in the same way as a speculative habit does. Neither art nor the speculative habit produces a good work with respect to use, which is proper to the virtue perfecting appetite, but only gives the capacity of acting well.
Summa theologiae, First Part of the Second part, Question 57, article 3