The identification of realism with ontological independence did not originate within science itself. It emerged from a philosophical transformation in the seventeenth century, when the relationship between the knowing subject and the world was reconceived in radically new terms.
At the centre of this transformation stands René Descartes.
Descartes did not set out to redefine realism. His project was to secure the certainty of knowledge in the face of scepticism. Yet the strategy he adopted reshaped the metaphysical background against which realism would later be understood.
In attempting to guarantee knowledge, Descartes introduced a division that would fundamentally alter the philosophical landscape: the separation of the thinking subject from the extended world.
The Method of Doubt
Descartes begins his philosophical project with a radical procedure: the systematic suspension of belief in anything that could possibly be doubted.
By applying this method of doubt, Descartes attempts to strip away all uncertain beliefs in order to discover a foundation for knowledge that cannot be questioned.
What remains is the famous conclusion:
Cogito, ergo sum — I think, therefore I am.
The existence of the thinking subject becomes the first indubitable truth.
But this starting point has an unintended consequence. Knowledge now begins with the certainty of the subject rather than with the world itself.
Two Substances
From this foundation, Descartes reconstructs reality as consisting of two fundamentally distinct kinds of substance:
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thinking substance (res cogitans), the domain of mind and thought
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extended substance (res extensa), the domain of physical matter
The thinking subject is characterised by consciousness and awareness.
The physical world, by contrast, is defined entirely in terms of spatial extension and mechanical motion.
This dualistic framework introduces a sharp conceptual separation between the knower and the known. The mind exists in one domain, while the physical world exists in another.
The question of how knowledge reaches the external world now becomes unavoidable.
The New Meaning of Reality
Because the subject and the world have been separated, reality must now be defined in a new way.
The physical world must exist independently of the thinking subject. If it did not, knowledge of the external world would collapse into mere ideas within the mind.
Thus the concept of reality becomes tied to independence from thought.
Reality is what exists outside the sphere of mental activity.
This marks the birth of the independence doctrine.
It is not introduced as a definition of realism itself. Rather, it arises as a solution to a philosophical problem created by the new subject–object division.
But once introduced, the idea quickly becomes embedded in the modern conception of the world.
The Mechanisation of Nature
The Cartesian framework also redefines the nature of physical reality.
In earlier traditions, the world was understood in terms of forms, powers, and relations within a structured order of causes. For Descartes, by contrast, the physical universe becomes a vast mechanical system.
Matter is characterised solely by extension in space.
All physical phenomena are explained through the motion and interaction of extended bodies.
This mechanistic conception reinforces the idea that physical properties belong intrinsically to objects themselves. Position, size, and motion are treated as features of bodies that exist independently of observation.
The world appears as a domain of intrinsically defined objects interacting according to mathematical laws.
Within this framework, independence realism becomes almost unavoidable.
A Philosophical Inheritance
The significance of Descartes’s transformation cannot be overstated.
By separating mind and world, he created the modern philosophical problem of how knowledge relates to an external reality. By defining physical matter as extended substance governed by mechanical laws, he provided a framework that seemed to support the existence of intrinsic properties.
Together, these moves established the conceptual background for modern scientific realism.
Reality came to be understood as what exists independently of observation. Objects were thought to possess intrinsic properties that measurement merely revealed.
Yet this framework did not arise from empirical discovery. It was a philosophical inheritance shaped by the attempt to secure certainty in knowledge.
Later developments in physics would appear to confirm this picture, giving it an aura of scientific inevitability.
But its origins lie not in experimental science, but in a particular metaphysical reconstruction of the relationship between mind and world.
Toward the Classical World
The next stage of the story shows how this philosophical framework became naturalised within science itself.
When the physics of Isaac Newton achieved extraordinary predictive success, the Cartesian conception of reality as a domain of intrinsically defined objects seemed to receive decisive empirical confirmation.
The world described by classical mechanics looked exactly like the kind of world Cartesian metaphysics had prepared us to expect.
And so the independence doctrine became woven into the conceptual fabric of physics.
But the apparent harmony between the two would not last forever.
The classical picture would eventually encounter a theory that refused to fit inside it.
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