(Modern and Medieval Languages, Cambridge)
The simple and immediate answer to this is that the image is real, but the tree clearly is not, even though it may be a real picture of a real tree. Yet philosophers have always had problems with the notion of reality and our knowledge of it. In commonsense, everyday terms most of us have no problem telling what is real and what is not. Yet when you start to think about trying to define just what reality is, it becomes much more elusive.
Is the test of reality, for instance, a commonsense test – something we see with our own eyes? That seems valid at first, especially since the evidence of our eyes is often backed up with evidence from other senses. But can you be sure it’s real? Could it disappear as soon as you stop looking? Could it all be a dream? Or a hologram? How can you tell that you are not just a brain in a vat fed a virtual reality by some mad scientist? And might even memory be an illusion, too – and the world burst into existence a few minutes ago, with all our memories intact? Descartes asserted that the only thing you can be sure of is that you are thinking, an idea summed up in his famous phrase, ‘
Cogito ergo sum
’ – ‘I think therefore I am’.
One of the problems with visual evidence is that very often our eyes see things differently at different times or are tricked altogether. The sky looks black at night but blue by day. A dress that appears white in sunlight may appear
yellow by candlelight. Railway lines seem to converge in the distance. Things far away look much smaller. On hot days, illusory puddles shimmer on the road. The Greek philosopher Plato talked about how what we think of as reality may actually just be like shadows from a fire playing on the cave wall where we have been bound captive all our lives – when reality is the real objects revealed in bright sunlight. Plato proposed that beyond the shifting, imperfect world we perceive is another realm of perfect, unchanging Forms, an inner reality as brilliant as the sunlit world outside the cave that gives the shifting shadows their substance. Although philosophers have largely abandoned this Platonic vision, it has remained a source of fascination for fiction writers ever since.
The English philosopher John Locke got round the problem of illusions a different way. Human understanding, Locke suggested, is like ‘a closet wholly shut from light, with only some little openings left, to let in external visible resemblances, or ideas of things without’. We don’t actually see real things at all, even though they may be there, but instead create or ‘represent’ them in our minds from purely visual sensations. In other words, seeing a tree is like seeing a picture of a tree in our minds and seeing someone sit down beneath the tree is like seeing a film of it. If so, our painting of a tree may actually be said to be no less real than a ‘real’ tree, because it’s simply a representation of the image of the tree the artist sees in his or her mind.
However, one of the problems of this ‘representative realism’ is that you then have to ask who’s actually doing the watching. Descartes saw the mind effectively as a stage (later called the Cartesian theatre) on which ideas and perceptions are viewed by an inner observer or ‘homunculus’. But just who or what is the homunculus, and who’s watching inside the head of homunculus? It begins to sound like some absurd Russian doll.
That’s why some philosophers, such as Berkeley, insisted that it was pointless to ask whether something had a reality outside our perception. There is no way we can be sure the world has any other reality. Berkeley insisted that ‘
esse est percipi
’ – to exist is to be perceived. In other words, reality exists only as long as it is perceived. If I blink, reality disappears momentarily. But this, though quite logical, is solipsistic, and so counter-intuitive that we’d probably regard someone who genuinely believed it as slightly unhinged.
Maybe the best guess is that we do live in a world of real things, and that these real things are what cause our sense experiences, an idea known as causal realism. It sounds self-evident, but the crucial thing is that the real object causes the experience, so there is a direct link between the real thing and our sensory experience. It’s an assumption which cannot be proved by logic – we cannot know we are not just brains in a vat – but it’s the most fruitful way of treating reality, and there is no evidence to contradict it.
We are reasonably confident that when we look at a tree we are looking at a real thing, and this is borne out by others also seeing the tree – although they might see it differently. Similarly, we are reasonably confident in our sensory experience of a painting to say that we know the painting itself is real. Equally, we can be confident enough in our senses to say that the tree in the painting is not real, but simply a representation of a tree created by the artist. The tree may be a representation of a real tree, or it may be the representation of an imaginary tree, created in the artist’s mind, maybe as a result of seeing real trees or being told about them. The artist chooses how to represent the tree – whether it’s ‘realistic’ like a pre-Raphaelite painting, which the viewer instantly connects visually to a real tree, or entirely abstract like a tree by Picasso.
(Experimental Psychology, Oxford)
This is such a seemingly simple question, yet it throws up challenges that have baffled both philosophers and scientists. One of the problems, of course, is defining just what consciousness is.
In commonsense terms, it just means being awake and aware. A snail, like most animals, is able to sleep and wake up. A snail is also, like other animals, aware enough of particular features in its environment to respond to them, choosing where it goes and how it reacts – even if it’s only at its own particularly languid pace. But we know, from our
own experience, that there is much more to consciousness than this.
The problem is how to get inside an animal’s head and know just how it thinks. Consciousness is a very private experience. It’s hard enough to know what consciousness is like for other humans, when we have the benefit of language and many other ways of communicating to tell us. It’s almost impossible with animals, so we have to infer from things they do and the way they react.
There’s always been a tendency for we humans to regard ourselves as rather special and different from other animals. While it’s clear that physically we have much in common with other animals, we’ve also liked to think that our brains are somehow special, and many thinkers from Aristotle onwards have suggested that we are uniquely conscious. Sometimes human consciousness is described as ‘self-awareness’ – the idea that we know that we are conscious, and are aware of who we are. It used to be a commonplace that only humans recognised themselves in a mirror. But then it was shown that apes, elephants and dolphins do, and more recently even little magpies with their birdbrains have proved they can, too. Even though we might think it’s unlikely, it’s hard to imagine a test to prove for certain that a snail cannot recognise its own reflection. Moreover, there is no reason to assume that an animal, especially one so fundamentally different, experiences consciousness in the same way that we do – so even a proven
failure of the mirror test would not prove anything about snails.
Over the centuries, countless philosophers from Descartes to Daniel Dennett have speculated on just what consciousness is, and for Descartes being aware of thinking was the single basic truth of existence. In recent years, the notion of consciousness has been explored by psychologists and neuroscientists, as well as thinkers about artificial intelligence. While philosophers try to work out just what it all means, scientists such as Francis Crick and Roger Penrose have tried to explain where and how it occurs physiologically in the brain.
Most thinkers agree that understanding consciousness is one of the hardest of all intellectual problems. In his 1989
Dictionary of Psychology
, British psychologist Stuart Sutherland wrote: ‘Consciousness is a fascinating but elusive phenomenon; it is impossible to specify what it is, what it does, or why it evolved. Nothing worth reading has ever been written about it.’ Not everyone is quite as pessimistic as this, and there were small signs of progress at least in spring 2009, when French scientists showed that consciousness is a coordinated activity involving the entire brain – and not located in a particular place.
Recently, British psychologist Nick Humphrey suggested that animal consciousness may have started with the way a creature keeps track of its response to the environment and then evolved as the ability to privatise and internalise these tracking responses developed into a
sense of self and a will to survive that gave the creature a competitive edge. If this is so, there is no reason to think that consciousness cannot have developed right through the animal kingdom, down to the level of snails. If snails have this kind of self-awareness, it’s clearly nothing like as sophisticated as our own, but it might be a mistake to assume that they are simply rather gelatinous automata.
Thinkers on consciousness have sometimes divided it into two kinds, which were labelled ‘access’ consciousness and ‘phenomenal’ consciousness in 1995 by American linguist and philosopher Ned Block – although not everyone agrees there is such a division. ‘Access consciousness’ is being aware of information in the mind and being able to access it. ‘Phenomenal consciousness’ is simply experiencing things without any physical response. Feeling pain, tasting coffee, hearing music are all such experiences or ‘qualia’, as they are sometimes called. Some thinkers suggest that qualia are the difference between ordinary humans and zombies. Zombies have no qualia, so no inner life, and are thus nothing more than puppets.
In the 1970s, Thomas Nagel wrote a famous paper, ‘What is it like to be a bat?’ in which he summed up the experience of qualia as ‘what it is like to be’. He then went on to suggest that we cannot yet imagine any way of knowing what it’s like to be a bat (or a slug or any other animal, including humans) – and any physical theory of consciousness cannot be considered until we have some way of understanding this subjective experience of the world. This is sometimes described as the ‘hard problem of consciousness’ (as opposed to easier to understand access consciousness). Other thinkers, such as Daniel Dennett, deny the division of consciousness and the ‘different’ quality of qualia altogether, and believe that there is just one all-embracing kind of consciousness. At the moment, though, the answer must be that we know very little – less than the snail …
(Biochemistry, Oxford)
Well, strictly speaking, there isn’t; there are only dissolved chemicals which combine to make salt when precipitated, and which give seawater a salty taste. So far, 72 separate elements have been found in seawater, and the chances are that nearly every natural element on earth is in there somewhere. However, the most abundant by far are ions of chlorine (about 55.3 per cent) and sodium (about 30.8 per cent), the elements that combine to make common salt. The other relatively common ions are magnesium (3.7 per cent), sulphur (2.6 per cent), calcium (1.2 per cent) and potassium (1.1 per cent). It’s these six elements that make seawater salty or ‘briny’.
On average, the salinity of sea water is about 35 o/oo, which means 35 parts salt to a thousand water. That’s a huge amount of salt – the equivalent of a teaspoon of salt
in a glass of water. Estimating the total volume of water in the oceans, you can work out from this concentration that overall there is a staggering 50 million billion tons of salt in the sea – and that if all the salt were extracted from the oceans it would cover the entire earth to a depth of 500 feet!
The salt concentration varies from place to place, though – as we know mostly from a worldwide series of chemical tests conducted in 1884 by William Dittmar aboard the British corvette HMS
Challenger
. It’s highest in the Red Sea and Persian Gulf, and lowest in the Baltic and the Arctic Ocean. This variation gives us a clue about why there is salt in the sea in the first place. Levels are high in warm seas, where evaporation of pure water leaves salt behind in the water and increases salt content; and low in cooler seas, where pure water is continually added from melting ice and rivers.
The oceans probably formed originally as water vapour ‘degassed’ from the molten rocks that once covered much of the hot early earth, formed clouds and then rained as the earth cooled. The original ocean waters were pretty much freshwater, but the salt content gradually built up as salt was added from three main sources – rivers flowing into the sea, hydrothermal vents on the sea floor and undersea volcanoes.
Rain falling on the land (and the oceans) is pretty much pure water (made slightly acidic by dissolved atmospheric gases). That’s why rivers are freshwater rather than salt
water. Although they are usually fresh-tasting, however, rivers are never completely pure. Instead, they contain tiny traces of salts and other solids – some the fragments of weathered rock, others dissolved directly from susceptible rocks such as limestone as water seeps through the ground on its way to the river.
It’s estimated that some 4 billion tons of salt are washed into the sea every year from rivers around the world. At that rate, it would take about 200–300 million years to give the oceans their salt content. The rivers don’t dilute the ocean because just as they add freshwater, so freshwater continually evaporates from the ocean surface. That’s why salinity tends to be lowest on the ocean margins where rivers continually flood in freshwater, and highest in mid-ocean. But why haven’t the oceans got steadily saltier and saltier, then, as more salt is added and water evaporates? It’s thought that they have now reached a balance where the salt content stays steady. Each year, much the same amount of salt is precipitated out of the oceans to settle on the ocean floor as is added to them by rivers.
Interestingly, ‘freshwater’ rivers tend to carry much more calcium, bicarbonate and silica than ‘saltwater’ in the sea. Seawater, however, contains much more sodium and chloride. One of the reasons for this is that marine life plays quite a significant role in the chemical balance of the oceans. A lot of calcium is taken out of seawater by the huge numbers of creatures such as molluscs, crustaceans, foraminifera and corals that use calcium to build skeletons and shells. Diatoms extract silica. Other creatures affect the chemical composition in subtler ways, such as snails that extract lead and sea cucumbers which secrete vanadium.