The philosophical tradition, particularly since Descartes, has grappled with the relationship between mind and matter, often positing a world of physical objects existing independently of our perception. Indirect Realism, or representationalism, became a dominant view, suggesting that we apprehend the external world not directly, but through mental representations or ideas. This perspective, advanced by thinkers like John Locke, proposed that our senses provide us with immediate ideas, which then allow us to infer the existence and nature of a material world beyond those immediate sensations. However, this seemingly intuitive framework faced significant challenges, most notably from Bishop George Berkeley's subjective idealism. Berkeley argued that the very notion of a mind-independent material substance was incoherent and unnecessary, proposing instead that "to be is to be perceived" (esse est percipi). This essay will explore the core tenets of Indirect Realism and then detail how Berkeley's Idealism fundamentally dismantled its assumptions, offering a radically different account of reality.
Indirect Realism posits a dualistic universe where both minds and material substances exist. For Locke, our minds are furnished with ideas through sensation and reflection. Sensation provides us with ideas of external qualities, like the colour red or the warmth of fire, while reflection offers ideas of our own mental operations. Crucially, Locke distinguished between primary qualities (like solidity, extension, figure, motion) which he believed were inherent in objects themselves and bore a resemblance to our ideas of them, and secondary qualities (like colours, sounds, tastes) which he argued were powers in objects to produce sensations in us, and did not resemble our ideas. The implication of this distinction is that while we can have a veridical representation of an object's primary qualities, our perception of its secondary qualities is more subjective. The external world, according to this view, is the cause of our sensations and ideas, but we never directly access this world. Instead, we are confined to the realm of our own perceptions, inferring the existence of a material substratum from the regularity and coherence of these perceptions. This reliance on inference, however, opens the door to skepticism: how can we be certain that our ideas accurately correspond to an external reality we can never directly experience?
George Berkeley, in his Treatise Concerning the Principles of Human Knowledge (1710), launched a direct assault on the concept of mind-independent material substance, the bedrock of Indirect Realism. His central argument is elegantly simple: the idea of matter existing unperceived is an absurdity. When we try to conceive of a thing existing without a mind to perceive it, we inevitably imagine it as perceived – by ourselves or by some other perceiver. Berkeley argued that all our ideas are passive and dependent on the mind. Qualities such as colour, warmth, hardness, extension, and figure are all perceived by the senses, meaning they are inherently tied to a perceiver. To speak of a "quality" existing without a mind to experience it is, for Berkeley, to speak of nothing. He famously used the example of a cherry: its redness, its roundness, its tartness are all sensory experiences. If the cherry were to cease being perceived, then, according to Berkeley, its colour, shape, and taste would cease to exist. He contended that Locke’s primary qualities were no more independent than secondary ones; extension, for instance, is experienced as a visual or tactile sensation, and thus is as much a perception as colour.
Berkeley replaced the notion of material substance with spirit, or mind. For him, reality consists of two kinds of substances: finite spirits (human minds) and an infinite spirit (God). Objects of perception – what Indirect Realism calls "ideas" or "representations of material objects" – are simply collections of sensations that are impressed upon our minds by God. The regularity and order of the universe, which Locke used to infer the existence of material causes, are for Berkeley evidence of God's constant and consistent activity. The tree outside your window continues to exist when you are not looking because God perceives it, and thus it is sustained in existence. This God-centered idealism resolves the problem of unperceived objects and avoids the skepticism inherent in Indirect Realism’s representational gap. It also offers a more parsimonious explanation, as it eliminates the need for an unobservable, inert material substratum that somehow produces our perceptions. Berkeley’s argument is not simply an epistemological challenge about what we can know, but an ontological one about what exists.
In conclusion, Indirect Realism, while attempting to bridge the gap between mind and an external world, ultimately relies on an unproven and, for Berkeley, an incoherent concept: mind-independent material substance. By insisting that all that exists are minds and their perceptions, Berkeley’s Idealism provides a radical alternative. It posits a universe where reality is fundamentally mental, sustained by the divine mind, and where the problem of skeptical doubt regarding the external world is dissolved, not by inferring an unknowable substance, but by re-conceptualizing the very nature of existence itself.