“Form Fits Function” as a General Theory of Knowledge

“What is its structure, and what does it do?” That is how biologists look at any feature of the body. And what would it be like if that methodology was applied more generally to knowledge? Would that be a fruitful way of organizing what we know?

How would it be different?

ABSTRACT. The phrase “form fits function” has been incorporated into several disciplines, such as design in engineering, fashion regarding clothing, and in biology. In this essay, I take the sense used in biology and wonder if that can be applied to philosophy in a more general way so as to make it into a theory of knowledge on the order of, say, Platonism or materialism. I specifically compare it (to show what I mean by a general theory of knowledge) to the Enlightenment views that the world works by everything following physical laws and/or inner essences. The sense of “form fits function” used in biology is to see everything as having both a structure (what it is made of) and a function (what it can do). And here my question is: Can we see the entire world (not just biology) in that fashion? Should we look for form and function everywhere, the way that the Enlightenment looked for laws everywhere? Can knowledge itself be structured that way?

I come to argue that describing form fits function is one of the major activities of science, along with making equations and mechanisms. It explains why biology succeeds so well in spite of not having many formal equations. Form fits function turns out to be a potent way of handling very complex situations, as occurs in biology, but also for dealing with randomness, as I elaborate in Causality in a World of Random Actions. This essay here describes the main tenets of form fits function and anticipates and answers objections. Applications can be found in the essays “Form Fit Function in Evolution” and “Theories of Explanation.”

First of all, to put some perspective on it, it would be different from the standard Enlightenment view of the way that the world works. Instead of predominantly seeing “objects following laws” (biology has few equations), we would see “structures having functions.” (That might seem teleological at first, but it is not—it is biology—as I will address later).

Furthermore, in the Enlightenment view, objects are characterized as reflecting pure essences (so that a blackbird has the essence of bird-ness plus the essence of blackness), whereas in biology the structures come from how particular things are fitting together in particular ways. And in the Enlightenment view, the laws are said to apply to everything, whereas the biological functions apply just to what is doing that fitting together.

The biologists seem to be taking account of what is fitting together, and a succinct and easy way of doing that is with the structures and functions. That is what I want to examine further.

Is the Enlightenment view even justified in skipping over this fitting together business (by only acknowledging pure essences and laws that apply to everything)?

tenets of form fits function

It turns out that there are a lot of ways of understanding the world differently once we use this biological approach. But for here in this essay, I am going to concentrate on just one of them, which is to look more closely at how the biological approach itself works. The biologists have a phrase “form fits function,” and that is what I will examine to try to discover some insights about how to proceed in this biological methodology. (That will also show how it is not teleology).

To repeat, biologists ask the question of anything, “How is it put together, and what does it do?” Or more technically, “What is its structure, and what is its function?” But the mantra, “Form fits function” implies much more than that. It implies that there cannot be one without the other.

The structure creates the function, and vice versa. They cannot be separated. Or more exactly, the structure and function exist in terms of how the other is also present.

That is not a necessarily intuitive notion, and by sheer force of willpower it is frequently violated outside of biology. For instance, in fashion there is another phrase, “Form over function,” which means that clothing should look good even when feeling bad. So with fashion, the point is that, when it comes to human behavior, we can indeed separate form from function. But in nature, the two go together. (And usually that is even the case in human affairs. When we say “form over function,” we are admitting that we are violating what feels right).

So consider a screwdriver. We cannot fully describe its structure unless we take into account how it is used for turning screws. To make sense of it having a blade to insert into the screw, we must understand the screw itself and how it has threads that are driven into the wood by the turning of the screwdriver. Also, to understand the shape of its handle, we must understand the structure of our hands and how they can grip the screwdriver in order to turn it. But conversely, we cannot fully appreciate the function of the. screwdriver without knowing these details of its structure and that of the screw and our hands.

So it is likewise in biology. Darwin, for instance, made much of how the shape of a bird’s beak matches with its function for eating seeds, insects, or other birds. The structure and function evolve together.

But that is very different from the Enlightenment view of objects having features just because of having pure essences reflected upon them from a Platonic heaven and then being pushed around by laws that are said to apply to everything. In the Enlightenment view, “what things are” and “how they move” are determined separately and do not depend on one another as in “form fits function.” (An interesting aside, however, is to note that the physical laws do not actually work on “everything” in any case, as when helium molecules rise instead of being attracted by the earth’s gravity. It turns out that what happens does depend on the structure of what the law is applied to, after all).

not teleology

So is it teleological, to see the world writ large as the biologists do?  (Teleology is to see things in inanimate nature as acting with goals or purposes rather than acting meaninglessly as in law-following or causality. Often, the goals and purposes are said to be there “by design”).

The issue arises, of course, because the word “function” is similar to the word ‘purpose.” The function of the heart is to pump the blood, but also the purpose of the heart is to pump the blood. Historically, some philosophers even argued that it should be taboo for scientists even to use the word “function”—that was considered to be unscientific—since that implies teleology. Scientists were instead to say that the molecules in the heart are just following the laws of nature and that it only seems to our minds that that is having a purpose.

But biologists have pretty much ignored that prohibition against using the word “function.” That is because it is impractical to do otherwise. It is not feasible to describe, say, the lungs, without talking about breathing as their function. Or it is not possible to really grasp the notion of wings without mentioning flying.

The biologists understand that to describe either a structure or a function requires describing the other, as well. To fully elucidate what it means for the structure of the eyes to be a certain way requires making sense of that structure in how it enables seeing. And to fully understand how the eyes can be used for seeing likewise requires knowing the details of their structure. To describe one requires describing the other. (And a similar argument applies to breathing and the lungs, or to any part of the body).

Form fits function.

And no one can accuse biologists of being against evolution and in favor of design—they were the ones who invented it and argued for it to others—but they also understand how structure and function evolve together so as to adapt to the environment. A change in one affects the other, and vice versa, so they come into existence together via evolution. The shape of the wings and being able to fly are together what survives natural selection. Or the construction of the eyes and being able to see are together what lives or dies.

Besides, biologists, when they see an organ such as the heart, do not say, “What is it for?” (as in a teleological design), but rather they ask, “What does it do?” (as in how does its structure fit together with itself and with its environment in a way that enables some action).

So the biological approach is not teleological—it is not to say that things have purposes because they were designed that way—but rather it is to recognize how evolution works as a natural process, to create form fitting function.

It is not really necessary, after all, to view the world in the Enlightenment fashion in order to be “scientific.”


Then once we understand that, we can ask ourselves what else we might understand differently if we see structures having functions rather than objects obeying laws. For instance, a comparable argument can be made for it regarding the physical world, as when atoms fit together in certain ways to make stable molecules (structures) but not in other ways which are not functional as molecules (so that they fall back apart).

Even that perversion of form fits function, “form follows function,” (said in industrial design) seems wrong to me. It seems that in the mind of the designer an image still evolves as a structure can be formed with a function in mind, but then it is adjusted as the function is pictured with the new tentative structure in mind; and back and forth, so that the final image evolves with each adjustment.

And that brings up how evolution works, which is to have a lot of attempts at making something until one appears where form and function work well together.

Of course, this FFF approach of the biologists is not the only way to see the world–and I realize that it might seem bizarre to those schooled in Enlightenment thinking—and for that matter, the biologists are not a uniform lot themselves. But it is a valid way of organizing knowledge. It is a means of incorporating the role of evolution into our descriptions of the world, since form and function evolve together to make the world what it is.

And in any case, it clearly enables solving problems that are unsolvable using the standard Enlightenment precepts. If nothing else, it enables us to describe body organs having functions when that is taboo under Enlightenment thinking. Another example is recognizing analogies by seeing how certain setups have the same function. (That can even be lifesaving, as in recognizing danger that way. It means that the ability to recognize functions in nature confers survival value, making that ability even more likely to evolve still further).

Indeed, look out the window and try to find anything that is not in some sense functional. To find the function, look to see how it is fitting together with other things, to do something. Even a rock is functional. It might be as a perch for an insect or bird. Or you could pick it up and throw it as a weapon. It all depends on what it is combined with, to do something.

Functions exist because of how one structure fits together with other structures, to do something. And nature is capable of fitting together. That means that functions are not just concepts of the mind, but rather they exist really in nature (because things fitting together exists really in nature).

We can start to get a picture of a more complicated expansive world—one full of possibilities—when we see things combining to have functions, compared with the Enlightenment view of pure essences being pushed around by laws. With functions, we can explain more complicated events that way (as in biology).

It works to see the world—and our knowledge of it—as organized in this fashion of structure and function fitting together. And arguably, that even applies to daily life, not just biology. It can be used in theories about how to deal with ethical dilemmas, and how to organize society, and even in business decisions, not to mention issues in ontology such as functionalism and reductionism, or how to have an actually intelligent artificial intelligence.

I personally suspect that advances in both AI and cognitive science await a recognition of FFF approaches instead of Enlightenment era thinking. When one event crashes into another, it does more than set off how the next one crashes into the next and the next. It creates how there can be structures and functions made along the way, supervening the literal physical events, and making new activities occur “in terms of” these expansive qualities, so that it becomes a matter of how the structures and functions themselves combine into ever newer structures and their functions.

So FFF is not without its applications outside biology.

Even the “shapes” of ideas can evolve by considering how they function in various applications.

It all makes sense because the world is made of energy, and energy moves (as recognized in the Enlightenment view), but also energy makes arrangements of itself.

And arrangements fit together.


The phrase “form fits function” is used and explained in Neil Campbell’s extraordinary textbook in biology, simply titled Biology, fourth edition (1996)page 9 (Benjamin Cummings, Menlo Park, California). It should not be confused with later editions which bear the name of the late Campbell but which were not written by him.

My website: dealrasmussen.com

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