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The Ontology of Abstract Objects: Do Numbers Really Exist?

Key Takeaways:

  • Platonism and nominalism present contrasting views on the existence of numbers, with Platonism advocating for their independent, abstract existence and nominalism viewing them as human-made constructs.
  • Contemporary theories like fictionalism, structuralism, and formalism offer nuanced perspectives that challenge traditional views by focusing on the utility, relational aspects, and syntactical nature of mathematics, respectively.
  • The debate over the existence of numbers is not just theoretical; it influences practical applications in science and technology, and shapes philosophical discussions about the nature of reality and knowledge.

Ontology, the philosophical study of the nature of being and existence, addresses some of the most profound questions within human thought. Among these is the intriguing debate over the existence of numbers. This question does more than challenge our understanding of what numbers are; it compels us to explore deeper metaphysical questions about the nature of abstract objects. Are numbers real entities existing independently in an abstract realm, or are they mere human constructs without existence outside of our minds?

This debate features two prominent views: Platonism, which posits an independent existence of abstract objects, and nominalism, which denies this and views numbers as conceptual tools.

Understanding Abstract Objects

Abstract objects, such as numbers, propositions, sets, and musical works, differ significantly from physical objects. Unlike an apple or a chair, abstract objects cannot be perceived through senses—they are neither visible nor tangible.

What distinguishes abstract objects most clearly is their unchanging, atemporal, and aspatial nature. They do not age or undergo physical transformations, nor do they exist in time and space as do the objects of our everyday experiences. This makes them fundamentally different and often leads to debates about their actual existence. Philosophers use these properties to define and argue about the status of numbers and mathematical entities, which are central to disciplines ranging from mathematics to philosophy itself.

The Case for Platonism

The philosophical position of Platonism traces back to Plato’s theory of Forms, which proposes that abstract forms (or ideas) represent the most accurate reality. Modern Platonists extend this concept to numbers, arguing that they exist independently of human minds and physical reality, residing in an abstract realm. This view is compelling because it aligns with the universality and necessity of mathematical truths found in nature and human creations. For instance, the principles of mathematics apply universally, whether in the orbits of planets or the design of a smartphone, suggesting a transcendent realm of mathematical truths.

However, Platonism is not without its critics. One major criticism involves its ontological commitment to a world filled with non-empirical entities, which some argue adds unnecessary elements to our understanding of the universe. Critics also question how we can access and interact with these abstract entities if they are not part of the physical world we inhabit. This challenge questions the coherence of Platonism and whether it offers a plausible account of abstract objects.

The Case for Nominalism

Nominalism opposes the Platonist perspective by rejecting the independent existence of numbers and abstract entities. According to nominalists, numbers are not discovered as pre-existing entities but are invented as tools by humans to better organize and describe the world. This view posits that numbers are essentially linguistic constructs—symbols in a complex system of communication that help us categorize and manipulate our understanding of the world.

For nominalists, the effectiveness of mathematics is not due to the existence of numbers in some abstract realm but because humans have developed these concepts to correspond closely with observations and practical applications. The strength of nominalism lies in its simplicity and economy of assumptions: it avoids the metaphysical baggage of assuming an unseen realm of abstract entities, thus adhering more closely to empirical and observable realities.

Contemporary Views and Theories

Beyond the classical dichotomy of Platonism and nominalism, several contemporary theories offer fresh perspectives on the ontology of numbers, providing varied explanations for the nature and existence of mathematical entities.


Fictionalism in mathematics posits that mathematical entities are akin to characters in a story—they don’t exist in any tangible form but are useful for the purposes of storytelling and reasoning. This view suggests that mathematical statements are not literally true but are useful in much the same way that fictional stories are.

Philosopher Hartry Field is a notable proponent of this perspective. He argues that mathematics is a powerful fiction; through the lens of fictionalism, mathematical truths can be seen as ‘true within the fiction of mathematics’. This approach allows us to use mathematics effectively without committing to the existence of abstract mathematical objects, sidestepping ontological commitments while preserving the utility of mathematics in scientific theories and everyday calculations.


Structuralism shifts the focus from individual numbers or mathematical objects to the relationships between them. According to structuralists, mathematics is fundamentally about different structures, not about objects in themselves. This theory views numbers as positions within a structure or system, such as the natural number structure or the real number system.

Structuralism can be divided into two main types: ante rem structuralism, which posits that structures exist independently of any instances, and in rebus structuralism, which asserts that structures exist only insofar as they are instantiated in physical systems. This perspective helps to explain the apparent objectivity and consistency of mathematics without requiring a realm of abstract objects.


Formalism, closely associated with David Hilbert, argues that mathematics is essentially a game involving the manipulation of symbols according to agreed-upon rules. From this viewpoint, mathematical statements do not make claims about the world but simply follow from the rules of the mathematical system. Thus, the truth of mathematical statements is derived from the manipulation of symbols rather than from correspondence with any external reality.

Formalism effectively sidesteps metaphysical questions about the existence of numbers by focusing on the syntactical, rather than the semantical, aspects of mathematics. This theory emphasizes the creative and artificial nature of mathematical knowledge, viewing it as a construct of human intelligence designed for specific purposes, such as solving problems and predicting phenomena.

Numbers in Practice

The application of numbers in practical fields like physics and engineering often presents a compelling case for their quasi-reality. In these disciplines, numbers play a critical role in modeling and predicting natural phenomena, from the quantum scale to the cosmological, suggesting a universal applicability that transcends their theoretical origins. This practical indispensability might seem to support Platonism, but it also strengthens the nominalist argument when considered through the lens of human ingenuity and adaptation.

Numbers may not necessarily derive their utility from existing in a Platonic abstract realm. Instead, their effectiveness lies in their ability to describe and predict patterns in the universe, making them indispensable tools in both theoretical and practical realms. From engineering marvels like bridges to complex computer programming, numbers prove their worth by providing a reliable foundation for development and innovation.

This widespread utility prompts a deeper exploration into the nature of numbers: Are they merely conceptual tools—useful fictions crafted by humans—or do their consistent applications in science and technology hint at a deeper, potentially elusive reality? Such questions challenge us to reconsider the fundamental nature of numbers, blurring the lines between mere tools and inherent truths of our universe.

Philosophical Implications

The exploration of numbers and their ontology not only deepens our understanding of mathematics but also influences broader philosophical domains such as epistemology and metaphysics. The debate touches upon fundamental questions about the nature of knowledge and existence. For instance, if numbers are understood as real, independent entities, this suggests a universe rich with invisible, unobservable truths waiting to be discovered, reflecting a reality that extends beyond human perception.

Conversely, viewing numbers as mere human constructs points to a reality where knowledge and existence are intimately tied to human capacities and limitations. This perspective foregrounds the creative and interpretive acts involved in human cognition, suggesting that our reality is shaped as much by the limits of our minds as by the external world.


The question of whether numbers really exist invites us to reflect on the profound nature of reality and our place within it. While Platonism offers a universe of eternal truths, nominalism grounds our understanding in human-centered pragmatics. Theories like fictionalism, structuralism, and formalism provide nuanced middle paths that bridge these extremes.

Ultimately, the debate is not merely academic; it affects how we understand everything from the basic laws of physics to the technology we develop and the very way we perceive the world. As we continue to probe the depths of this philosophical issue, we may find that the nature of numbers—and indeed the nature of reality itself—is more complex and intertwined with human thought than we initially perceived.

Further Reading

To delve deeper into the philosophy of mathematics and the ontology of numbers, consider exploring these additional resources:

  1. Philosophy of Mathematics: Selected Readings” by Paul Benacerraf and Hilary Putnam – This classic collection includes seminal papers that have shaped the philosophy of mathematics.
  2. Thinking about Mathematics: The Philosophy of Mathematics” by Stewart Shapiro – Shapiro offers a comprehensive overview of contemporary philosophy of mathematics, including detailed discussions of structuralism and other positions.
  3. Science without Numbers” by Hartry Field – Field presents a compelling case for a nominalist approach to mathematics, arguing against the independent existence of mathematical objects.
  4. Platonism and Anti-Platonism in Mathematics” by Mark Balaguer – Balaguer explores the debate between Platonism and nominalism in the context of modern mathematical practice.
  5. The Road to Reality: A Complete Guide to the Laws of the Universe” by Roger Penrose – While not solely focused on the philosophy of mathematics, Penrose’s work explores the relationship between mathematics, physics, and the nature of reality.

These texts provide a range of perspectives that can enhance your understanding of the philosophical questions surrounding the existence of numbers and extend your exploration into how these concepts influence other areas of thought and science.