Santa Claus is not real, but books about him are
One old test for what is real says a thing must be able to make a difference. Gandhi passes: he moved millions. Santa Claus fails, since he cannot act on anything. Yet the children's books about Santa pass easily, because they shape what people think. Defining reality turns out to be surprisingly slippery.
Philosophers use reality in two senses: the sum of everything that exists, from rocks and trees to stars, or the quality all real things share that separates them from illusions. The word comes from the Latin res, meaning thing, and appeared in English in the early 1500s. It is often set against appearance, how things seem versus how they are, though some thinkers argue these are two ways of framing the same things rather than two separate realms.
The causal test just described is known as the Eleatic principle, from ancient Greek philosophy. Its weakness is that numbers and other mathematical objects cannot push anything around, so it seems to rule them unreal. A second criterion says real things are independent of minds: a virus behaves according to its nature whether or not anyone knows of it, while Gandalf would vanish if nobody had ever imagined him. That raises an awkward question about thoughts and memories, which seem real yet are mental. A third test counts dreams, mirages and hallucinations as unreal because they misrepresent the world. J. L. Austin, working from ordinary language, argued that real always means real of some kind, as in a real diamond versus a fake, or a real duck versus a decoy.
Neighbouring ideas complicate matters. Alexius Meinong held that being is broader than reality and includes things that do not exist. David Lewis's modal realism claims countless possible worlds exist, each as real as ours, and the many-worlds interpretation of quantum physics has the universe branching so that every possible measurement outcome occurs. Actuality is often contrasted with potential, as with an acorn that could become an oak but has not yet done so.
Realists hold that reality exists independently of human knowledge; anti-realists think some parts of it depend on minds, perspectives or social conventions. The debate stretches back to ancient Indian, Chinese and Greek thought, and virtual and augmented reality now raise fresh questions about what kind of existence digital objects have.
Source: Reality
