“Inclusion” has become a celebrated value in politics, corporate PR literature and education, but as I’ve argued previously, in order to include you have to exclude. If you’re not part of a group that has an exclusive identity, it’s impossible to be inclusive. Now let’s take it a step further.

How does this observation relate to “diversity,” especially since the two terms are paired so frequently?

Diversity and inclusion are in a conceptually hierarchical relationship. Whatever else diversity means, it at least captures the existence of empirical differences among human beings—different colors of skin, different ethnicities and cultures, different sexes, different languages, different values, etc. Yet marking these kind of differences tells us nothing about what to think or do about them.

That’s the job of inclusion: to practice inclusion is to incorporate difference into sameness, whether that sameness takes the form of a university, church, theater troupe, or any other group. Thus, while diversity can make sense without appealing to inclusion (you can define something as different without asking if it should be included into something else), inclusion only makes sense given the recognition of diversity (you can only ask if something should be included if you’ve already recognized its difference from that into which you want to include it).

Which One Is Not Like the Other?

That does not mean, however, that diversity makes sense as a stand-alone concept. Think, for example, of what it means to say human beings are different from each other, even only in the physical sense: to say that one human is taller than another, or has more muscle mass, or is missing a limb presumes that we already have a standard template for the meaning of “human” upon which we are identifying differentiation. Without that template, we would not know what changes and what remains the same from person to person.

One philosophical way to capture this relationship between a being and its attributes is to distinguish between the “essence” and “accidents” of something. The essence of something is that which fundamentally defines the being as a being; a being’s accidents, on the other hand, are those features of a being that can change without changing the being’s essence.

For example, it is an essential feature of human beings that we possess an upright posture, which requires a common skeletal structure. However, the length and mass of the bones that make that posture possible can and do differ among individuals (and, even, within an individual’s own life). Same, too, with the power of speech. Speech makes us human from an essential perspective, but the actual words we use can and do change without altering what it means to have the power of speech. And while we share other traits like opposable thumbs, having hair, and having two eyes with other animals, the girth of our thumbs, and the thickness of our hair, and the color of our eyes (all of these, of course, within limits) varies substantially from human to human without generating the question “Is this a human?”

Out of One, Many

Taking the essence-accident model as a guide, we can say this: essences can exist without accidents, but accidents cannot exist without essences. Or translated into friendlier terms, unity can exist without diversity, but diversity cannot exist without unity.

The most basic reason why this is the case is that difference as a concept requires a stable, unified reference point to give it meaning. The same is not true with unity. It is possible to say something is without a comparative framework. However, to say something is other — that is, to say it is different or diverse — does require a comparative framework, namely a reference point of something that already is.

The great medieval theologian St. Thomas Aquinas captured this insight in its grandest sense by arguing that only God, by virtue of being God, is. Everything else in existence can only exist because it participates in God’s is-ness; in so doing, everything is thus both related to God (and to each other) as having a common creator and fundamentally different from God insofar as it is created. In other words, every form of diversity that exists in the world only exists because of the one primordial difference between God and that which God creates, which is just another way of saying that unity — in the form of the divine in this example — is the condition for the possibility of diversity in existence.

It is crucial to add here that even if you conceive of God differently than Thomas Aquinas — indeed, even if you reject the existence of God altogether — it is still necessary from a conceptual perspective to locate unity as more foundational than difference, including when making empirical differentiations. For example, to identify the differences among species, you need the fixed, unified categorization of “species” itself; the same goes for “genus,” “family,” “order” and so on.

The empirical differences both within groups and among them are only intelligible because they exist within a unified framework of sameness. So, too, from a linguistic standpoint: adjectives need nouns in order to have any meaning, but nouns can have meaning without adjectives. Even from strictly empirical and grammatical perspectives, in other words, something must first be in order for it to be different.

Applied Metaphysics

But how could this conceptual framework possibly matter for how we speak about diversity in a moral and political sense? Let’s examine two common affirmations about diversity, each with a different meaning.

Celebrate Diversity! This affirmation suggests that difference is good in and of itself.

Diversity Is Our Strength! This affirmation, in contrast, suggests difference is good because it leads to good consequences.

Let’s start with the first affirmation. What does it mean to say that we celebrate diversity because difference is good in and of itself? It must at least imply that we have a clear understanding of what “difference” means. However, as noted above, the condition for the possibility of difference being intelligible is that it has some reference point to that which is not different. So if diversity is good in and of itself, then that must also mean that that which is more foundational to diversity — unity — is not only also good but also better insofar as it is only because of unity that diversity can exist.

A possible alternative to this view is the position that diversity is possible without reference to any sameness and, therefore, could be pronounced as good without implying any conception of unity. I’ve argued against that possibility above, but let’s say that someone responds by taking a nominalist position, or a position that declares that all “universals” are fictions and, therefore, only individuals exist. In this sense, the counter-argument could go, we “celebrate diversity” by recognizing that everything is different from everything else and claim that to be good.

But there’s a problem here. From a philosophical perspective, nominalism is not the friend of any “diverse” group and certainly not the friend of any “diverse” individuals. If it is true that only individuals exist, then that means that everything in existence must be broken down to its smallest possible ontological expression, which, in turn, means that the “human individual” — especially in the political and moral sense of “the autonomous bearer of rights” — is, like every other categorization, a fiction.

Every individual can be divided into much smaller parts, and those parts into much smaller parts, until we are talking about atoms, electrons, and quarks. If nominalism’s the name of the game, in other words, it’s nominalism all the way down, which would mean that “celebrate diversity” could only mean celebrate sheer and absolute difference, which would be a celebration of everything and nothing all at once.

What about the claim, “Diversity is our strength”? Like the above example, this claim can only make sense in relation to a unified, fixed understanding of some kind of sameness to which diversity can contribute. That is clear from the expression itself: if diversity is our strength then that means there is a deeper unity that defines the “us” that serves as the foundation for diversity.

Second, claiming that diversity is our strength also presupposes that the group that constitutes the “us” has a unified, shared goal towards which they are working. “Strength,” by itself, is vacuous; it must be for something to give it meaning. So to claim that diversity is our strength means that diversity helps us to achieve our goal as a group. Note, however, that the goal, whatever it is, must necessarily condition what kinds of “diversities” the group can cogently embrace.

A group of atheists, for example, will not be strengthened by choosing a believer to lead them, nor will a constitutional democracy be strengthened by electing a tyrant, nor a tech company strengthened by selecting a Luddite. In other words, both the meaning and goodness of diversity in the claim “Diversity is our strength” is conditioned by a more foundational unity — namely, the group’s identity and goals.

We Are Not the Same, But We Are One

The two claims about diversity, in other words, appear to confirm the article’s original position on the relationship between diversity and unity. Barring embracing absolute difference, we can only say, in the end, that diversity a) exists and b) is good within a horizon of unity. That insight, of course, doesn’t mean diversity is morally and politically unimportant, nor does it tell us what should unite us. But it does demonstrate that every time we invoke diversity, we are necessarily implying a deeper unity. Maybe that deserves some celebration, too.