What you studied as ‘physics’ or metaphysics in the ancient world would depend a great deal on what tradition of philosophy you primarily belonged to. Epicureans, for example, held that physical and metaphysical questions mattered only to the extent that getting the answers to them wrong led us to be disturbed and unhappy; getting interested in them for their own sake was a misuse of time that would be better employed learning more directly how to live well. The Stoics thought it important to get right the major metaphysical points about the world: it is governed by providence, and a rational appreciation of it will discern how everything in it is for the best. But they were not much more interested than the Epicureans in getting the details right for their own sake.
Among ancient philosophies it is the Aristotelian tradition which has the broadest and most generous conception of what the study of nature is. Aristotle had the reputation of being the philosopher most interested in causes and explanations. And, although his account of nature is not one that we, with our modern scientific knowledge, can still accept, we can still appreciate the main lines of it as embodying a response to our world which is highly worthy of respect.
Plato’s ‘theory of Forms’
Plato has no explicit theory of Forms. In some dialogues, especially Phaedo, Republic, Symposium, Phaedrus, and Timaeus, there are passages, some with argument and others more expressive and metaphorical, which introduce in various ways items we usually call Forms, but for which Plato never develops a standard terminology.
In contrast to the things in our experience which are beautiful, Plato introduces the idea of the ‘beautiful itself’, which is beautiful in a way not relative to context or time or perspective. Unlike all the beautiful things and people in our experience, the beautiful itself is never not beautiful. This idea is developed with value terms like beautiful, just, and good, and with mathematical terms like double and half. It is notoriously unclear how Plato’s arguments could be extended beyond terms with opposites. Despite a widely misinterpreted passage in the Republic, Plato does not think that there is a Form for every general term; Forms are not what came to be called universals. There is a Form only where there is an objective nature that can be known by being intellectually grasped; Forms are always associated with using your mind to reason, as opposed to relying uncritically on your sense experience. The most famous passages about Forms stress this contrast between the mindless assumption that what experience impresses on you is just what there is, and the critical use of reason to grasp realities, the Forms, that are accessible only to the enquiring mind.
In the dialogue Parmenides Plato shows that he is aware of apparent inconsistencies in what he has said about Forms. The right response, however, he holds, is not to abandon Forms but to continue to argue on both sides until a defensible position is reached. He continued in this spirit, never successfully producing a definitive theory of Forms. Later philosophers have often simplified the issues, but Aristotle and late twentieth century philosophers have explored the different arguments Plato employs for and against the existence of Forms.
For Aristotle, nature is the world made up of things that have natures. What is it to have a nature? It is to be a thing which has a source internal to itself of changing and being changed. We can understand what a lion is only by looking at lions themselves and at the way they interact with their environment and other species. To understand an artefact like a shield, by contrast, we have to appeal to something external to the shield itself – the designs of humans that made it. Things with natures are primarily living things, such as plants and animals, including humans. For Aristotle, then, nature is, right from the start, not just whatever happens, the undifferentiated totality of what there is (as it is for Mill and others from the nineteenth century on). Nature is already a world of things that organize themselves and live characteristic lives, and to understand nature is to come to understand what kind of lives these are. Nature is active, a system of living and changing things. There is no hint in Aristotle of the view, notorious in many scientists since the early modern period, that nature is passive, lying out there to be mastered by the scientific mind.
Still less is there the even more notorious idea that nature is there for us to exploit. For Aristotle, skill and expertise take further what nature has begun. He is thinking of farmers who breed grasses to produce food crops, and of cooking as a process of predigestion to enable us to consume otherwise inedible foods. It never occurs to him to think of technology as invasive of nature. (Doubtless this is partly because he is not aware of any technology sophisticated enough to do this.) Nor does it occur to him that human activities might upset nature’s established balances. Humans hunt and eat animals and fish in the way these hunt one another and eat plants; it is all part of a self-regulating system. Many of Aristotle’s ideas are, tragically, bound to sound quaint in our world, where humans have intervened disastrously in the workings of nature, wrecking ecosystems and exterminating species. For Aristotle the species, including humans, have always been there and always will be; what we want is to understand how they all fit in overall. That is why, in a famous passage, he defends the study of the ‘lower’ animals and how they work as being as worthy a human study as the grander study of the heavenly bodies. ‘For in all natural things there is something wonderful.’
For Aristotle, we want to understand nature, including ourselves as parts of nature, because it is natural for humans to want to understand things. Isn’t this circular, though? Yes, but the circularity does not matter. Aristotle’s theories are naturalistic in the modern sense; they accept that the processes by which we come to understand nature are themselves a part of nature. They are not something mysteriously exempt from the conditions they study. Philosophy, including the study of nature, begins in wonder; we are puzzled and interested by what we find around us, and do not feel satisfied until we have adequate explanations for it. The search for explanation thus does not point beyond itself; for Aristotle it would be beside the point, as well as foolish, for us to try to understand nature in order to exploit it for our own ends. Hence, although different methods are appropriate for studying different areas of nature, we are puzzled, and seek explanations, in our own case in the same way as happens with other living and non-living things.
Explaining is finding out why things are as they are, and for Aristotle there are four basic ways of doing this, his so-called ‘four causes’, which appeal to what he calls form, matter, the moving cause, and the final cause, what the thing is for.
Aristotle is aware that his demand for teleological explanations, explanations in terms of final causes or what something is for, is contentious. He knows of previous thinkers who held that there are no goals in nature, and that we and the world around us are the contingent products of random events. Animals’ teeth, for example, were held by some to be the product of random combinations of material, some of which turned out to be suited to animals’ needs while others were not.