Idealism is the philosophical position that says reality only exists within the context of ideas and thoughts. In other words, reality is a mental entity, not a physical one, and there is no reality external to consciousness and thought. Idealism contrasts with materialism (see here) and realism (which says that reality exists independently of our capacity to conceptualize it).
Plato was the first major figure of idealism. He argued that the ‘real’ world consists of idealized Forms separate from our own material world. It is sometimes said that he was not a true idealist because he acknowledged a material world of sorts, or else he is labelled a realist (since his Forms exist to some extent independently of being conceptualized). However, others insist he is a pure idealist because his basic contention is that ‘true reality’ exists only in the realm of thought. He theorized that prior to our earthly existence, we inhabit a world of Forms and bring the memory of these ideal Forms into our earthly souls. Thus, for instance, we recognize that a dog is a dog because we are born imbued with the concept of the ideal dog in our minds. Whether sheepdog, greyhound or bull terrier, we recognize each as variants of the ideal dog. And as for dog, so for anything else you can think of: cars, flowers, colours, biscuits – even concepts such as justice and virtue. Our material realm, Plato said, consists only of ‘shadows’ of the ideal forms of ‘true reality’.
Immaterialist idealism
In the 17th century, René Descartes toed an idealist line of sorts by concluding that we cannot be sure of the existence of anything other than our own selves, whose existence is evidenced by the very act of thinking (see Rationalism here). Then, in the 18th century, the Irish philosopher and bishop, George Berkeley, devised the theory of ‘immaterialist idealism’ or ‘subjective idealism’ – perhaps the most complete doctrine of idealism hitherto described. Rejecting the existence of material substance, he insisted that an object only exists to the extent that it perceives or is perceived – existence, in other words, is reliant upon conceptualization. However, he allowed for the existence of apparently unperceived objects by accepting God’s perception as universal and eternal. So, for example, a tree may fall down in the middle of a forest even if there is no human to see or hear it because God observes it.
German idealism
In the 17th century, Immanuel Kant spearheaded the influential school of German Idealism. He considered philosophy had so far failed in one of its chief goals: to determine once and for all whether there is an external world entirely distinct from ourselves. In his Critique of Pure Reason, he said that the mind is a blank slate, on to which we inscribe knowledge acquired by observation of the external world. Then, he suggested, the mind is pre-arranged to allow us to organize, structure and make sense of experiences. As our mind moulds our perceptions of reality, we may only know things as they seem to us (what he called phenomena) but cannot grasp a ‘thing-in-itself’ (something as it is in its true nature external to our minds – what he called noumena). He went on to describe how the human mind is pre-programmed with concepts such as space and time, causality and substance, to assist us in experiencing life in a meaningful way. Kant thus believed that we should be content with the reality of our perceptions, and give up on the vain goal of comprehending an external reality beyond the reach of our intellectual faculties. By accepting our limitations, he said, our minds may be set free – a philosophy sometimes described as transcendental idealism.
Another important strand of idealism was the so-called absolute idealism championed by G. W. F. Hegel in Enlightenment-era Germany. His sometimes-elusive philosophy teaches that there exists an all-inclusive unity, comprising all events, phenomena and ideas, in what he characterized as the Absolute Spirit (a sort of universal mind and soul) that is revealed to us through the process of history. It is an ideology that influenced, among others, Karl Marx and Friedrich Nietzsche. Indeed, idealism in its various guises has informed the thinking of many of the world’s foremost philosophers and forces us to confront the deepest questions of what we are and what we mean by reality and the ‘real world’.