Modal Ontology

On the Nature of Possibility

Figure 1: Poised above the unknown, a man mid-leap above a puddle—umbrella in hand, fate in motion.^[1]

What does it mean to talk of modal ontology, to say something is possible—that it might happen, or could have turned out differently?^[2]

We talk this way all the time, but rarely ask: Where does possibility live? Is it just in our heads? In the rules of logic? Or is it somehow out there, woven into reality itself?

Imagine a lottery. Before the draw, every combination could win. Possibility feels wide open. Then the balls drop. Ultimately, one outcome becomes real—and all the others vanish.

Some philosophers argue that every possible outcome does happen—just in another world. Our universe is simply the one where this result occurred. Others say possibilities aren’t real at all—just tools we use to reason about what might have been.

This article explores what possibility really means—not as a puzzle for specialists, but as a force that shapes every choice we face.

Classical Views on Possibility

The ancient Greek philosopher Aristotle was one of the first to tackle the problem systematically. For him, possibility wasn’t about imaginary scenarios—it was about potential, the natural capacities hidden inside things.^[3]

Consider the example of the acorn and the oak tree. The acorn is potentially an oak tree; it can become one. But the acorn is not actually an oak tree. Only the full-grown tree is.^[4]

A stone, on the other hand, will never grow into a tree, because its possibilities are limited by what it is. Aristotle saw the entire world this way—as a place where objects and living things are constantly moving from what they are toward what they could be.^[5] In this view, possibility is like an invisible blueprint guiding how things change.

Centuries later, the German thinker Gottfried Wilhelm Leibniz proposed a very different idea. He imagined God as a kind of cosmic architect, selecting the the best of all possible worlds. In this view, our universe is just one version of how things could have been—a single volume in a vast library of realities. The other 'books' in this library—the worlds where history unfolded differently, where dinosaurs never went extinct, or where you were born in another country—aren’t physically real, but they could have been, because they don’t contain any logical contradictions. For Leibniz, possibility was about consistency: something is possible if it obeys the rules of reason, even if it doesn’t exist in our world.^[6]

Not everyone agreed that possibility was a feature of reality. The Scottish philosopher David Hume argued that our sense of what’s possible is really just a product of experience and habit.^[7] When we say something 'could happen,' what we actually mean is that we’ve seen similar things happen before. For example, we call it 'possible' for a car to skid on ice because we’ve witnessed it before—but if we’d never seen ice or cars, the idea wouldn’t even occur to us. Hume believed that possibility is just a way our minds organize expectations, not a real force in the universe.^[8]

Immanuel Kant, writing in the 18th century, tried to bridge these perspectives. He argued that possibility isn’t just in our heads, nor is it purely 'out there' in the world—instead, it’s built into the very structure of how we perceive reality. Time, space, and cause-and-effect aren’t things we discover; they’re the lenses through which we see everything.^[9] So when we say something is 'possible,' we mean it fits within these mental frameworks. A world where gravity doesn’t exist isn’t impossible because of physics alone—it’s impossible because we literally can’t conceive of a coherent experience without it. For Kant, possibility is the boundary of what makes sense to a human mind.

These classical debates might seem abstract, but they shape how we still think about possibility—often without realizing it. When scientists speculate about parallel universes, they’re echoing Leibniz’s 'possible worlds.' When we weigh decisions by imagining outcomes ('What if I take this job?'), we’re using something like Aristotle’s idea of potential. And when we struggle to picture something truly alien to our experience (like a color outside the visible spectrum), we’re bumping against Kant’s limits of thought.

Underneath it all is the same unresolved question: Is possibility a shadow cast by reality, or is it something real in its own right? The answer changes how we see everything—from the laws of physics to the choices we make every day. In the next section, we’ll see how modern philosophers have pushed these ideas even further, asking whether 'possible worlds' might be more than just metaphors.

Modern Views on Possibility: When 'Could Be' Becomes Real

The 20th century blew the door wide open on how we think about possibility. Armed with new tools from logic, physics, and even computer science, modern philosophers began asking harder questions: Are possible worlds real places? Is the future truly open, or just unknown? Can something be 'possible' without being imaginable? Their answers would reshape everything from artificial intelligence to how we understand our own choices.

David Lewis and the Reality of Parallel Worlds

In 1968, American philosopher David Lewis dropped a philosophical bombshell: Every possible world is as real as our own.^[10] Not as metaphors or stories—as actual, physical universes. In Lewis's view, when we say 'Nixon could have lost the election,' we're pointing to a parallel universe where that really happened. These worlds aren't connected to ours, but they exist just as concretely, with their own versions of you making different choices.

What makes our world special? Nothing, says Lewis—we just call it 'actual' because we're in it, the same way we call our location 'here.' This radical idea (called modal realism) solves tricky problems in philosophy, but at a cost: it means reality contains infinitely many versions of everything that could possibly exist. Unsurprisingly, not everyone was convinced.

Kripke's Comeback: Possible Worlds as Tools

Saul Kripke, one of Lewis's sharpest critics, offered a more practical alternative: Possible worlds are useful fictions, not real places.^[11] Think of them like scripts for unwritten plays—they help us analyze statements like 'The moon could be made of cheese' by imagining a consistent scenario where it's true. But no second universe is required.

Kripke's approach (inspired by his work in logic) became the standard in fields like computer science and linguistics.^[12] When a programmer tests all possible states of a system, or when we say 'That could never happen,' we're using Kripke-style possibility—not invoking alternate realities, but exploring consistent descriptions.

Heidegger's Radical Shift: Possibility as Human Freedom

Meanwhile, German philosopher Martin Heidegger was asking a completely different question: What does it mean to live possibility? For Heidegger, humans aren't just objects with fixed properties like rocks or trees—we're beings who face possibilities.^[13] Your 'could be' (a musician, a traveler, a different version of yourself) isn't out there in some parallel world; it's part of how you exist right now.

This existential view influenced psychology and education. When we talk about 'potential' in students or therapy patients, we're channeling Heidegger's idea that human existence is fundamentally open-ended.^[14]

Deleuze and the Virtual: Where Math Meets Jazz

French philosopher Gilles Deleuze took this further with his concept of the virtual—not 'fake', but a realm of unrealized potentials that shape reality like invisible forces.^[15] Imagine:

• A chess game where every possible move exists as a kind of pressure on the player.^[16]
• A jazz improvisation hovering between infinite notes before one is played.
• The way social media algorithms feed on our 'possible' clicks before we make them.^[17]

For Deleuze, the universe isn't a collection of finished worlds (Lewis) or tidy models (Kripke)—it's a simmering field of tendencies waiting to crystallize into actual events. This idea now fuels theories in complexity science, digital culture, and even quantum physics.^[18]

Possibility in the Wild: From AI to Activism

These abstract debates have concrete teeth in modern life:

• Quantum physics wrestles with whether all possible outcomes really exist (as in the multiverse interpretation).^[19]
• AI safety researchers use possible-worlds models to simulate catastrophic scenarios.^[20]
• Climate activists argue about which futures are still 'possible' versus foreclosed.^[21]
• Video games create explorable possible worlds that feel paradoxically real.^[22]

The throughline? We're no longer just asking what is possible, but where possibility lives—in equations, in silicon, in collective action, or in the fabric of spacetime itself. The classical philosophers laid the groundwork, but today's thinkers are building skyscrapers on it.

The Conference of Difference: Possibility Without Elsewhere

In the Conference of Difference (CoD) model, possibility is not a pre-existing menu of options to be chosen from, nor a metaphysical warehouse of unrealized worlds. It is a relational tension—an affordance, a push and pull—that exists only through the interplay of distinct beings responding to each other’s partial moves. Possibility is not elsewhere. It is right here, where resistance transforms into rhythm.

Classical modal ontologies often imagine possibility in spatial terms: as alternate worlds, hypothetical spaces, counterfactual realms. In contrast, the CoD sees no need to posit other 'worlds'. What others treat as possible worlds, the CoD understands as zones of tension—potential but unrealized pathways within this world, latent within the ongoing dynamics of becoming.

In this framework, modality is not a fixed distinction across imagined domains; it is about adaptive ability in context. Possibility is not a detached property of a proposition, but a conditional affordance that emerges when beings engage in the conference of difference. Absent this conference, possibility itself collapses—there is no 'might' without relation, no becoming without tension. What we call 'impossibility' is not a logical status but the absence of ontological traction altogether. As such, the CoD organizes modal reality as a continuum of ability:

Figure 2: The Ability Gradient: From Absent to Enabled

This continuum does not describe a ladder of certainty, but the gradient of ability: not logical determinacy, but ontological traction. The CoD favors possibility over impossibility, probability over bare possibility and ability over mere probability—ever seeking the strongest ground from which realising may proceed.

Unlike Kripke’s semantics, which frame possibility as a tool for evaluating propositions, or Lewis’s modal realism, which multiplies ontologically sealed worlds, the CoD affirms a constantly unfolding existence shaped by recursive relation, not parallel instantiation. Each new act is not a leap into another world, but a co-produced deepening of this one.

This is a metaphysics not of might-have-beens but of what is still possible here, now, within the bounds of the beings involved. Possibility, in this view, is neither fictional nor transcendent. It is material, emergent, and ethically charged—a co-responsibility for what difference can still make possible through conference.

God, if the term still applies, is not the chooser of worlds but the conference of difference itself—that constant expression that makes existence possible.^[23]

Next week, we explore persistence and identity: what it means for a thing, a person, or a pattern to remain 'the same' even as everything changes. Is identity a fixed core? Or is it the memory of a pattern—a name passed around the table of time?

Stay tuned as we follow the thread of becoming into the question of being.^[24]

The Gospel of Being

by John Mackay

A rigorous yet readable exploration of how existence functions—and how that relates to you.

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