Compare direct realism, indirect realism and idealism as theories of perception and evaluate the problem of the external world

What this dot point is asking

You need to set out the three main theories of perception, explain the arguments that drive philosophers from one to another, and evaluate whether any secures knowledge of the external world.

Direct realism

Direct realism, or naive realism, is the common-sense view that in perception we are directly aware of physical objects and their properties. When you see a tomato, the red, round tomato itself is the immediate object of your awareness. Its strength is that it matches ordinary experience and avoids any sceptical gap between mind and world.

The classic challenge is the argument from illusion. A straight stick looks bent in water, a white wall looks yellow under coloured light, and in hallucination there may be no object at all. In these cases we are aware of something, yet it does not match any physical object. So, the argument runs, the immediate object of awareness cannot always be the physical thing. Direct realists reply by distinguishing how things look from what we perceive, or by appealing to relational or adverbial accounts, but they must do work to absorb these cases.

Indirect realism

Indirect realism, or representative realism, accepts the force of the argument from illusion. John Locke held that we perceive external objects indirectly, by means of ideas or sense-data that the objects cause in us. He distinguished primary qualities such as shape, size and motion, which resemble the object, from secondary qualities such as colour, taste and sound, which are powers in the object to produce sensations in us but do not resemble anything in the object itself.

The problem is that indirect realism opens a veil of perception. If all we ever directly access is our own sense-data, how can we know they accurately represent, or are even caused by, an external world? This is the sceptical problem of the external world: the representation could be exactly as it is whether or not any matter exists, as Descartes' evil-demon scenario dramatises.

Idealism

George Berkeley seized on this gap and pushed it to a startling conclusion. If we only ever have access to ideas, then talk of mind-independent matter behind them is empty. His idealism holds that to exist is to be perceived (esse est percipi); physical objects just are collections of ideas. There is no inert matter, only minds and their ideas. To explain why the world is orderly and continues when no human observes it, Berkeley appeals to God, who perceives everything continuously.

Idealism escapes the veil of perception because there is nothing hidden behind the ideas. The cost is high. It strikes most people as deeply counterintuitive, it leans heavily on God to do crucial work, and it struggles to explain the difference between perception and imagination without reintroducing something like an external cause.

Evaluation

The debate is a chain of pressure. The argument from illusion pushes the direct realist toward indirect realism; the veil of perception pushes the indirect realist toward either scepticism or idealism; and idealism's costs push some back toward a more sophisticated direct realism, such as the disjunctivism of later philosophers who deny that veridical and illusory experiences share a common factor. A good answer traces this dialectic and judges where the least cost lies, usually concluding that each theory trades intuitiveness against immunity to scepticism.