Is matter real? Do objects only exist in the mind of a perceiver? 18th century philosopher, George Berkeley, answered ‘no’ to that first question and ‘yes’ to the second. In his A Treatise Concerning the Principles of Human Knowledge, he claimed that esse est percipi, or ‘to be is to be perceived’; a thing only exists if a mind perceives it.
Berkeley’s idea seems unlikely today and even in his own era, he had a hard time finding converts. While tempting to ridicule, especially in the specific form Berkeley imagined it, there is nevertheless the glimmer of something deeply insightful in his philosophy. In this article, I will try to convince you of this.
Berkeley argued that the objects we perceive are nothing more than the ideas we have of them; that is, they exist only in the mind of the perceiver. The most immediate consequence of this, which Berkeley wholeheartedly embraced, is that there is no such thing as mind-independent, physical matter. There are two reasons Berkeley might have argued for this; the first I will call ‘internal’, the second, ‘external’.
The path I’ve called ‘internal’ I’ve done so because it starts from the mind and what it perceives. Berkeley notes that any object we perceive is, in reality, just an image (he calls it an idea) in the mind. In truth, we can’t be certain that this image in our minds correlates accurately, or even at all, with external reality. This was essentially what Descartes had argued just over half a century prior. However, where Descartes assumed there was actually an external, extended reality we could be more or less accurate in our knowledge about, Berkeley stops short of this assumption. All we really know for sure is that we have images in our minds; ‘I see a table, therefore I have an image of a table in my mind’, not ‘I see a table, therefore there is some substance in front of me that looks like a table’. In this, Berkeley was simply only willing to admit what he could know for certain. No matter how likely you may think it, the existence of some external, mind-independent substance called ‘matter’, is a hypothesis we can never definitively prove.
The ‘external’ path takes physical matter as its starting point. In Berkeley’s day, it was thought that matter was infinitely divisible, and he asks what this means. A particular piece of matter seems finitely extended and of a particular shape and size but given the infinite divisibility of matter, this can’t be true. On the contrary, each piece of matter must be composed of an infinite number of parts. Matter only appears finite because our senses aren’t acute enough to distinguish these smaller parts. Moreover, if we were able to perceive these parts, the size and shape of the piece of matter would vary as the acuity of our senses increased. During these changes in size and shape, the piece of matter itself wouldn’t change. What would change though, to produce these different impressions, is the sense; i.e. the perceiving subject. Berkeley’s conclusion: “Each body then considered in itself, is infinitely extended, and consequently void of all shape and figure… and it is the mind that frames all that variety of bodies which compose the visible world”.
Post-Berkeley – Sceptical Influences
18th century, Scottish philosopher David Hume carried on down Berkeley’s ‘internal’ path and found it goes right off a cliff. Because Berkeley denied the existence of matter, any knowledge we have of objects (which are really ideas of objects), we don’t obtain from the discovery of any “necessary connexion” between them. How could there be a necessary connection between objects that require the contingency of a perceiving subject to exist? Importantly, this means that the hypothesis of causality, which is a necessary connection between objects, is invalid.
Although I don’t think Hume denied the existence of matter, being the faithful empiricist he was, he did agree with Berkeley that causality is something we have no reason to believe in; that is, we can’t justify our belief in causality by appeal to reason. We presume the billiard ball will bounce off the cushion because we have seen it do so a hundred times before, but we can’t know it will by virtue of a law of physics. For all we know, the hundred and first time we roll the ball, it will just hit the cushion and stop dead. Hume didn’t stop at causality either. Carrying Berkeley’s insight to its natural conclusion, he tore through many of our cherished beliefs and assumptions with the same sceptical blade.
Immanuel Kant, a German philosopher about 10 years Hume’s junior, emphatically declared there is such a thing as extended, mind-independent substance. Nevertheless, he believed we could never actually know for sure what it was. This unknowable substance was what he called the thing-in-itself, and although it represents a step back from Hume’s radical scepticism, it still leaves us unable to fully believe our eyes, literally.
In addition to this sceptical strand in Kant’s thought, he also held that reality only appeared the way it did because human beings, through subjective faculties of perception (what Kant called categories), imposed structure on this unknowable thing-in-itself. According to Kant, time, space, causality, and nine other categories, don’t exist in the thing-in-itself; instead, human beings interpret formless, external matter according to these subjective, mental categories; in a way, creating reality by perceiving it. This is very close to what Berkeley said about objects existing only in the mind of the perceiver, which also leads us nicely into the next section…
Post-Berkeley – The Existential Link
When I read Berkeley’s account of what I called the ‘external’ path (section 47 in Berkeley’s A Treatise Concerning the Principles of Human Knowledge if anyone is really keen), I was reminded of Martin Heidegger and Jean-Paul Sartre who both argue, albeit in different philosophical frameworks, that world cannot be reduced to bits of matter floating about independent of consciousness.
That argument holds that world is not the abstract, third-person, theoretical constructs the physicist invents in an attempt to describe the interactions of particles and forces through mathematical equations. On the contrary, world is a meaningful concept imbued with significance, relevance, and value. None of these things exists in atoms and electrons. They only arise as the result of consciousness. Therefore, while physical matter, independent of minds, does exist, there is no world, without consciousness.
You might think this is just semantics, but I would argue it’s deeper than that. Consider an orange. Against Berkeley (and against the existentialists), science tells us this orange (part of a world) exists completely independently of a perceiving consciousness. Well, let’s take a leaf out of Berkeley’s book and see how far we can push science on this. What exactly is this orange? A collection of atoms, which lack any secondary qualities (colour, smell, taste, etc.). Already, our ‘orange’ that supposedly exists without consciousness has lost much of what made it an orange to begin with. But it gets worse, because the air around that orange is also made of atoms. So is the table it’s resting on. Ultimately, of course, there are differences in the numbers of subatomic particles making up the atoms in the different substances, and corresponding differences in the way those atoms are configured, but this is hardly a victory for the anti-Berkeley challenger because what we’ve just established is that unobserved, pure, objective reality, according to physics, is a sea of electrons, protons, and neutrons. That’s all. There is certainly nothing like our orange anywhere amongst all of those particles. To get our orange back, we would have to return, from pure, objective reality, to contingent, subjective perception. Without a perceiver, even though the atoms exist in exactly the same configuration, there just is no orange.
Post-Berkeley – Modern Physics
What about Berkeley’s claim that extended matter doesn’t exist? Surely, nobody has followed him down this rabbit hole. Actually, there are (at least) three very real, mainstream scientific reasons for believing something very similar to this. The first is just textbook physics. Electrons behave like both particles and waves. Some particles (photons and gluons) are massless. All particles get their mass when they go through a Higgs field; i.e. they don’t have mass, in themselves. Mass is energy. Granted, none of this is quite as extreme as Berkeley’s claim, in the sense that there is still something out there (energy, fields, waves, etc.), but as far as Berkeley went in denying the existence of extended (therefore massed) matter, it seems modern physics has to absolutely agree.
The second idea is that we might be living in a computer simulation. The objects that make up our world might not be composed of any kind of physical substance at all. Everything might just be strings of qubits existing in various quantum superpositions; i.e. information. Again, presumably this theory still requires the existence of something external to us (a quantum computer, for example), but, as with the first idea, the objects we perceive aren’t made of matter.
Finally, we have the idea that the universe is holographic. This theory postulates that all 3-D objects inside the universe are actually images projected from the 2-D surface, where all of the information is encoded. Once more, there is nothing substantial to the everyday objects in our world.
Berkeley didn’t deny the existence of everyday objects, nor did he argue that they are illusory. He simply thought they existed as ideas in our minds; ideas we all obviously share. Hopefully, I’ve persuaded you that what probably initially seemed like the ravings of a lunatic rather than the musings of a philosopher, is actually more like the latter.
What ultimately renders Berkeley’s philosophy, in the exact form he conceived it, untenable is the way he answered the question, what is the source of the ideas of sensation? He was clear that these ideas don’t come from corpuscular matter, but they must come from somewhere. That ‘somewhere’, for Berkeley, was God, who orchestrated (or orchestrates) everything so that the objects we perceive (i.e. ideas we have in our minds) behave as consistently and predictably as they do.
Still, while we might fault Berkeley for denying matter only to postulate something far less likely, it is nevertheless quite remarkable that science and certain corridors of philosophy have both, sometimes quite unintentionally, ventured further down the very pathways first embarked on by an Irish Bishop with a radical idea who lived three hundred years ago.
 Berkeley did not use either of these terms in his writings.
 I’ve talked about this in several other articles I’ve written. If you happen to have read those, much of this section won’t be particularly new.
 Let’s keep it simple and ignore things like quantum theory and string theory, neither of which change the argument in any relevant fashion anyway.