On Medical Analogies in Book 2 of Aristotle's Physics
On Medical Analogies in Book 2 of Aristotle's Physics
In this brief paper, I will examine a set of medical analogies made by Aristotle in Book 2 of his Physics. Taken together, these analogies help to define Aristotle’s concept of nature, and connect it to his other concepts about the workings of the world. An important statement is from the eighth chapter, in which he defends his claim that there are purposes, or final causes, in nature:
It is absurd to suppose that purpose is not present because we do not observe the agent deliberating. Art (techn) does not deliberate. If the ship-building art were in the wood, it would produce the same results by nature. If, therefore, purpose is present in art, it is present also in nature. The best illustration is a doctor doctoring himself: nature is like that. (Aristotle, Physics 199b26-30)
This is just one of the medical analogies found throughout Book 2, and I will return to analyze this statement after first looking at some of the analogies that precede it. In the first chapter, Aristotle seeks to distinguish what is natural in the world from what is artificial. He claims that animals and their parts, plants, and the simple bodies of earth, fire, air, and water are natural because they have an “innate impulse to change” (192b10-15). Products of human art, such as a bed or cloak, have no such innate impulse, except coincidentally in that they are made up of natural elements. Wood, as a product of nature, has its own innate impulse to change, and it is not something that results in a ship; otherwise, “it would produce the same results by nature,” that is, ships would be found in nature. He uses the following medical analogy to illustrate this further.
Someone who is a doctor might cause himself to be healthy, but it is not insofar as he is being healed that he has the medical science; on the contrary, it is coincidental that the same person is a doctor and is being healed, and that is why the two characteristics are sometimes separated from each other. (192b25-28)
A patient may happen to be a doctor, but that is not necessary; not all patients are doctors. In this analogy, a natural thing is like the patient-doctor, whose medical knowledge is compared to the innate impulse to change. The patient-doctor contains within herself the impulse to change—in this case, a cure of some kind. Artifacts are like the patient who is not a doctor: “no artifact has within itself the principle of its own production” (192b29-30). A human artisan is needed to finish the job, to create such things from their constituent elements into the forms that make them useful. Natural things, however, have their own ends, and it is this innate impulse to change that moves a natural thing to its end, defining its final cause. From this earlier medical analogy, it is already easier to see why Aristotle likens nature to a “doctor doctoring himself.”
The next medical analogy comes a few paragraphs later, in his discussion of the relationship between form and matter:
Further, nature, as applied to coming to be, is really a road towards nature; it is not like medical treatment, which is a road not towards medical science, but towards health. For medical treatment necessarily proceeds from medical science, not towards medical science. (193b12-16)
Aristotle uses this analogy to make the point that form speaks more to a thing’s nature than matter alone. The elements that make up a bone, as one of his examples goes, are at first mere elements. Once they take shape and become a bone, it is then more apt to call the thing a bone. Thus Aristotle shows that there is a direction to nature, using another example of a growing plant. The medical analogy brings this discussion to the relationship between an art and its end, which has more to do with form than matter. Medical treatment is a result of the medical knowledge that brings it about, and it is the medical knowledge, not the treatment, that contains the innate impulse to change. In this way, he aligns nature more with form as the outcome of change than with matter. He later takes this point even further by claiming that the formal, efficient, and final causes “often amount to one; for what something is and what it is for are one” (199a25-6).
Aristotle uses a medical analogy while discussing the various sciences, and argues that any science of nature should be concerned with both the form and matter of that which it studies:
Craft, however, imitates nature, and the same science knows both the form and the matter up to a point. The doctor, for instance, knows health, and also the bile and phlegm in which health is realized... (194a21-4)
In the next analogy, however, he stresses that the real reason to study nature is to understand what each thing is for, its final cause:
How much, then, must the student of nature know about form and what-it-is? Perhaps as much as the doctor knows about sinews, or the smith about bronze—enough to know what something is for. (194b10-12)
Aristotle thus views the final cause as chief among the other causes, which are more instrumental to understanding the final cause.
To defend his claim that natural things have final causes, Aristotle uses yet another medical analogy to account for the problematic case when a thing’s typical or expected end does not come about. He compares this case to when “doctors have given the wrong medicine” (199a35). His point here is that this is just something that can happen in any art, since nature, with its innate impulse to change, tends towards some end but does not necessarily reach that end.
I now return to the opening quote. Here Aristotle is answering the critic who claims that there are no purposes in nature. An innate impulse to change is central to Aristotle’s concept of nature. Both nature and artifacts require an impulse to change. In the case of a ship, it requires a shipbuilder. Nature, however, has its own innate impulse, and it is in this impulse that he situates the final causes of nature, which should be the central topic for the study of nature. He has argued throughout Book 2 that nature is not mere matter, but has form and an end as well. His view of nature as a doctor doctoring itself unites the analogies he has set up throughout Book 2.
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