By Mark Voigt, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=54796411

​Insistent Particularity 

"The Castle Rock at Edinburgh exists from moment to moment, and from century to century, by reason of the decision effected by its own historic route of antecedent occasions. And if, in some vast upheaval of nature, it were shattered into fragments, that convulsion would still be conditioned by the fact that it was the destruction of that rock. The point to be emphasized is the insistent particularity of things experienced and of the act of experiencing."

Whitehead, Alfred North. Process and Reality, emphasis is Whitehead's

It is noteworthy that, while Whitehead was a mathematician and metaphysician, he had a profound sensitivity to what he called "the insistent particularity" of things experienced—and of the act of experiencing itself. Imagine being struck on the head by a rock. Let's say the rock is a fragment of the Castle Rock at Edinburgh. The rock makes contact with an insistent particularity that cannot be reduced to abstractions about the nature of the rock, and the momentary pain you feel likewise resists reduction to conceptual categories. The insistent particularities of the world cannot be explained away by abstractions; they transcend them in their concreteness.

This holds true for all forms of experience, not just physical collisions. When we encounter another person, for example, that person presents a particularity that cannot be collapsed into our ideas or theories about them—a presence that is given to our experience. Even the Mind of the universe, even God, has an insistent particularity, grounded in divine decisions that belong to God, not to us. And we, too, embody such particularity in how we respond—to God, to others, and to the world around us.

​This insistent particularity is by no means limited to solid, bounded objects visible to the eye. The key is not to equate particularity with physical solidity. Other states of matter—liquids, gases, plasma—exhibit particularity, and so do sentient beings that may not appear as “material” in any obvious way. Past experiences, even when dimly remembered or shaped by interpretation, possess their own kind of particularity. So do the emotions of others, even when our comprehension of them is partial or uncertain.
This is what process philosophers mean by concreteness. It is, I suggest, the haecceity—the thisness—of the world and of God. It is different from the quiddity of the world and God, although both are real, What makes Whitehead's philosophy so interesting is that they occur within, not apart from, a world of becoming. 

 
​Quiddity and ​Haecceity

Whatness and Thisness in a World of Becoming

The philosophical concepts of quiddity and haecceity originate in medieval scholasticism, particularly in the writings of Thomas Aquinas and John Duns Scotus. Quiddity (from the Latin quidditas, meaning "whatness") refers to the essence or nature of a thing—what it is. It answers the question: What kind of thing is this? For Aquinas, quiddity represents the defining form or kind of a being—its universal nature. Haecceity (from haecceitas, meaning "thisness"), introduced by Duns Scotus, refers to what makes a thing this particular individual and not another. It is the principle of individuation that distinguishes one being from another, even if they share the same quiddity.

In classical metaphysics, these two concepts operated within a framework of substance and essence. Quiddity was tied to general kinds or universals, while haecceity provided the metaphysical glue that grounded those universals in concrete, particular existence. The assumption was that a thing’s identity could be captured by listing its essential properties (quiddity), and then distinguished from others through its unique thisness (haecceity), even if the nature of that thisness was not always fully explicable.
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Process philosophy, particularly in the work of Alfred North Whitehead, reimagines these concepts through a radically different metaphysical lens. In this view, reality is not composed of enduring substances with static essences but of actual occasions—momentary events of experience that come into being through processes of becoming and then perish. Within this framework, quiddity and haecceity are no longer static metaphysical attributes but dynamic, relational, and temporal elements of experience.

Quiddity in process thought refers to the pattern of eternal objects—Whitehead's term for pure potentials—that ingress into an actual occasion of experience. These eternal objects are the building blocks of qualitative reality: color, shape, texture, emotion, tone, and number, among others. An actual occasion integrates certain eternal objects into its becoming; these define its quiddity. In other words, quiddity is the “whatness” of the event—what it is like, what qualities characterize it. Two events can share the same quiddity, such as the same color, sound, or even emotional tone. But this does not make them the same entity.

Haecceity, on the other hand, refers to the unique act of concrescence—the process by which an actual occasion synthesizes its inherited data from the past, selects among relevant eternal objects, and brings them into a unified, subjective experience. Every act of becoming is a unique event, a moment of decision. Even if two events share the same eternal objects (and thus the same quiddity), the way they are integrated, the context in which they arise, and the subjective immediacy they embody will differ. Haecceity is this act of unrepeatable integration—what makes this occasion this and no other.

This processual view leads to a key insight: from Whitehead’s perspective, there are no true indiscernibles. The idea that two distinct entities might be described in exactly the same way—sharing all the same properties, with no possible distinguishing feature—is rejected in process philosophy. Even if their quiddities are identical, their haecceities are not. No two actual entities occupy the same position in the extensive continuum of space and time. No two entities inherit the exact same prehensive background from the world. And no two synthesize their influences in the exact same way. Thus, even “identical” events are metaphysically distinct because their becoming is distinct.

This distinction matters deeply—not just metaphysically, but existentially and relationally. Existentially, it means that each moment of a person's life, each decision, each act of feeling and responding, is a unique creation. Identity is not reducible to being a member of a class (a quiddity); it is constituted through the continual unfolding of haecceity—through what Whitehead calls “the self-enjoyment of becoming.” You are not simply a human, or a parent, or a teacher. You are this particular becoming—this act of integrating memory, possibility, context, and feeling in this moment. Your uniqueness is not a general fact about you; it is lived and created moment by moment.

Relationally, this view transforms how we see and treat others. In a world where it is common to reduce people to types or roles—customer, stranger, patient, immigrant—process philosophy insists that every being is a center of experience, an unfolding of unique haecceity. To respect someone fully is to recognize their individuality not merely in what they are, but in how they are—how they are becoming, feeling, struggling, hoping. It calls us to meet others not as categories but as unrepeatable acts of becoming, shaped by histories we may not see and possibilities we may not grasp.

In sum, the reimagining of quiddity and haecceity in process thought leads us to a more dynamic understanding of identity, difference, and dignity. Quiddity is the pattern of potential. Haecceity is the event of realization. Every actual occasion participates in possibility but realizes it differently. There are no static substances, no fixed essences. There are only acts of becoming—unique, unrepeatable, and precious.

In honoring thisness, we honor life itself—not as abstraction, but as the lived miracle of becoming.

"I’m taking a course in medieval philosophy, and we discussed the difference between whatness and thisness—between quiddity and haecceity. It struck me how often we focus on what people do, the roles they inhabit, the properties they exemplify—the 'types' of people they are. But in doing so, we overlook who they are: their irreducible, unrepeatable presence.
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And it's not just with people. We do this with everything. We pay attention to categories but not moments, to patterns but not presences. We’re drawn to what a thing is in general, but we miss that it is—here and now, in its singular being. Life is more than its properties."

- Imaginary college student majoring in philosophy