A more sophisticated hypothesis is presented by representative realism. Representative realists claim that the external world is not perceiver-dependent, but we perceive it indirectly. This means that we perceive it through an intermediary, which representative realists claim to be ‘sense data’. Sense data and the external world are distinctly different: sense data exist only within the perceiver’s mind (are private), are infallible (they may present us with false information about the external world, but there is no difference between our perceptions and our sense data) and exist only for as long as the perceiver is perceiving something (are temporary). The external world, however, appears to be objective, our perceptions of it are fallible and, the representative realist would argue, it is not perceiver-dependent. Another key aspect of representative realism is Locke’s idea of the primary and secondary qualities of objects. Locke argued that primary qualities, things such as number, solidity and extension, are objective. They exist physically in the external world. However, secondary qualities such as colour and taste are subjective: they are or could be perceived differently by everyone. Loosely using Russell’s table example, if a group of people are sitting around a table they will all perceive a table that is a certain size that can be measured and that is solid. However, if a meal were brought out onto the table and those people ate that meal, their experiences would not be the same, as the way one person perceives meat, for example, will be different to another’s, as taste is a secondary quality.
The theory of there being a barrier between us and the ‘outside world’ does have its problems, namely that if we are always perceiving our sense data, rather than the physical world, what evidence is there to prove that the physical world exists at all? A representative realist may argue that our being unable to create sense data at will shows that something outside of ourselves must be causing them, but this argument is not totally logically consistent. If Descartes ‘brain in a vat’ reality were true, the external world as we perceive it and the external world as it really was could possibly be completely different. We would have no control over our sense data, but there would still be nothing behind them.
Another possible criticism of representative realism is that Locke’s theory of the primary and secondary qualities of objects is false. Berkeley argued that in fact everything we perceive we perceive subjectively, so there are no such things as primary qualities. For example, to a child, an adult of average height would look very tall, although they would look small to someone who is 6’4”. Thus extension is subjective. We may be able to measure a person, but that measurement means nothing without perception. Berkeley argued that the external world is all perceiver-dependent: ‘esse est percipi’ (to be is to be perceived). There is absolutely no proof that there is anything behind our perceptions, therefore it is irrational to believe that there is. The only thing we know is our perceptions themselves. There are, however, problems with this view. One of these problems is presented by Russell’s cat. Russell asked, if a cat only exists when you are perceiving it, how come when you perceive a cat and then perceive it again hours later, the latter time it is asking for food? Berkeley’s answer lies in religion. He argued that since there is an omnipresent God, everything is always being perceived, therefore everything always exists. So what seems like an argument against the existence of an external world (if Berkeley’s view were correct the world would be external to us, but not to God) is actually nothing of the sort, since Berkeley would have us believe that this God that exists is eternal, and so the external world will always exist (as long as this God wishes it to). This argument from God may have been accepted in Berkeley’s time, but it is far from sound, and thus far from being reasonable.
In conclusion, it seems that no arguments for or against the existence of the external world are inferred with complete consistency. This could lead us to conclude that the only really reasonable view is ontological agnosticism with regards to the external world, however it seems to also be against sound judgement to live your life with no view whatsoever on such a matter. Thus it seems that the hypothesis that the external world exists is at least practically reasonable.
