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Complementarity & Reality

Alistair MacFarlane has complementary ways of looking at things.

In Boswell’s biography we are told how Dr Johnson, a naïve Realist, sought to refute the Idealist Bishop Berkeley’s claim that everything exists in the mind. He did so by kicking a stone, exclaiming: “I refute it thus!” But there are more enlightened things to do with stones than kick them. Suitably large, flat stones can be used as tables or seats. A smaller, lighter stone could be used to hold a door open or shut, and we would then call it a doorstop. If it seemed to us to have a pleasing shape and an attractive surface we might adopt it as an ornament. A set of small coloured stones could be used as counters in a game… and so on, in ways limited only by our imagination. What Johnson experienced, via his foot, was the physical reality of the stone, what we may call its facticity. But stones, while having one facticity, can have any number of what we may call functions. Seeing a stone as a possible table, seat, doorstop, or game piece is to see it in terms of its uses and meanings for us, to see it in terms of a possible function. A stone’s facticity is objectively demonstrable (Johnson’s point), but its function is an altogether more elusive concept. Meanings and uses are not material entities, so their reality cannot be demonstrated by any simple expedient such as kicking them (Berkeley’s point). Perhaps if Johnson and Berkeley had met in a face-to-face argument, Johnson might have lost his temper and flung the stone at Berkeley. His opponent may then have been temporarily convinced of the objective nature of the stone’s reality but, on recovering his wits, could have pointed out that Johnson had seen the stone in terms of a possible weapon, as a function rather than a mere facticity. A comprehensive framework for looking at the complex ways in which we interact with the world needs a broader conception of reality. It needs one that includes both physical and immaterial aspects. A way to achieve this is to use both of the complementary concepts of facticity and function. I call them complementary because we need both, and their combined use gives us a powerful framework in which to consider all the aspects of reality as we experience it in our daily interactions with the world.

Genesis of idea of complementarity

The idea of using two distinct, but equally necessary, attributes to describe a single entity arose in quantum mechanics. It was introduced by Niels Bohr, whose Principle of Complementarity is now one of the cornerstones of modern science. His deep interest in philosophy led him to urge a wider use of this idea, and complementarity is now used in fields as diverse as international law (complementarity of local and global jurisdictions) and linguistics (complementarity of different parts of speech). But it has not yet played a major role in philosophy. A way in which this might be done comes from the work of Wolfgang Pauli, another of the founding fathers of modern physics. Pauli, who was also deeply interested in philosophy, showed how the concept of reality may be extended beyond the narrow confines of physical science, in a lecture given to the International Congress of Philosophers in Zurich in 1954. His new definition of reality is strikingly general, clear and succinct: “That which we come upon, which is beyond our power of choice, and with which we have to reckon, is what we designate as real.”

The new ideas in physics admitted a necessary degree of indeterminacy into the behaviour of infinitesimally small particles. Up to this point (the late 1920s and early 1930s) determinism had been the bedrock of physical theory. Very small particles, like electrons, were now to be somehow associated with both particle-like and wave-like properties. Wave and particle were complementary descriptions of the same entity. Particle behaviour was coupled with a wave – a spatial distribution of its probable position. If the position of a particle became exactly known, for example if a photon collided with a photographic plate, then the wave vanished.

Those functions that we attribute to things (stones as chairs, counters, weapons…) are indeterminate until we establish them via an interaction (we sit on the stone-as-chair, count using stones-as-tallies, throw one at somebody…). This removal of indeterminacy by our interaction with things is analogous to the removal of a photon’s indeterminacy-in-position when it interacts with a photographic plate.

Evolution of functionality

Agency is a living organism’s capacity for autonomously interacting with its surroundings. In its simplest forms it can be understood solely in terms of physical reality. Simple agents, for example evolved ones such as beetles, or designed ones such as robots, contain physical representations of those parts of the environment with which they continually interact. This is a part of their evolved nervous systems, or their designed control units. Any continuing evolutionary development of such forms of agency will however run into insuperable problems arising from complexity. It is not feasible to evolve physical representations of the world to provide for every possible contingency that an agent might encounter. To do so would require a rigid prescription for every corresponding required action. This would lead to an unmanageable explosion of complexity. The evolutionary advantages of an alternative approach are obvious – functions, which guide an appropriate response, are built up piecemeal as a result of interactions with the world, and retained for use on an as-needed basis. The world provides its own representation, accessed as and when required. A price has to be paid however, which is that complete determinism is sacrificed for a degree of indeterminacy. An entity in the world will have one facticity but, for an agent, it can have any number of functions. The idea of complementarity in physics arose from dealing with very small energies; it arises in human behaviour from dealing with very great complexity.

We do not have a fixed, determinate set of structured responses to events in the world, as have robots or insects. Unlike such deterministic agents, our functionality is continually evolving. Our responses to the world, as inferred by other agents, thus have a fundamental indeterminacy. They are continually and flexibly generated from our contingent interactions with our surroundings, and with other people. Consequently our detailed behaviour can never be wholly predictable.

Social reality

In everyday life there are many not wholly material entities to be reckoned with, things which can kick us although we cannot kick them. Money is a good example. It cannot be characterized by a simple stone-like reality – try paying your bills with your own specially produced pieces of paper! Money, banks, laws which we must obey to keep out of trouble, and the courts we find ourselves in if we don’t, are all examples of what we can call social reality. These sorts of reality, which dominate our lives, can be characterized using complementarity.

How then do facticity and function combine in a complementary way to characterize the everyday reality of money? The facticity is straightforward – money is realized as paper, metallic coinage or, increasingly, as an electronically-generated pattern of information stored in a bank’s computer system. What makes it money is a socially-agreed, legislatively-backed function. The physical validation, for proof against forgery and so on, can be carried out by physical tests. The binding social agreements that ensure that particular pieces of paper are genuine ten pound notes are what establish the function of these pieces of paper as money. Banks are social realities in a similar way. Why some buildings are banks is because their operation is guaranteed by a set of social, legally-defined functions, governing the ways we interact with the people and systems in them.

It is useful at this point to introduce another pair of terms. We inhabit a world full of things to which we, and the society we live in, have allocated meanings and uses, to which we have allocated specific functions. Those for which functions have been allocated we will call objects (chairs, ornaments, weapons, ten pound notes, banks…). But the process can work the other way round – we can project meanings onto arbitrary things, in which case we call them symbols. Ten pound notes are symbols, pieces of paper which society has endowed with legally binding meaning and use. Systems of symbols enabling us to speak, read and write, and symbol-manipulating systems like mathematics, underpin all modern civilization. Wherever we look in our everyday world we see not mere things, but objects and symbols – we see a world suffused with meaning.

Complementary forms of reasoning

Some objects are used to help us to solve problems. We use them in complementary ways. Consider using a map to navigate unfamiliar terrain. Maps are collections of symbols that can be interpreted by applying rigidly-prescribed rules. This is how a satellite-navigation system uses the maps embedded in it. Give your starting and final destination points, and it will issue a set of precise instructions to get there (“Turn right at the next junction.”). But we often use maps in a different way – we look at them and interpret what they mean (“Let’s go up to that ridge, and then …”).

There are thus two complementary aspects to the creation and use of maps. They must be coherent under an appropriate set of rules for their creation and use (they are syntactically correct). And the maps must correspond to the way the world is; they must be coherent under an agreed set of meanings (they are semantically correct). The early days of sat-navs produced many stories of unfortunate lorry drivers who followed the devices’ rule-driven instructions without paying sufficient attention to their meaning. These complementary forms of reasoning, which we may call respectively syntactic and semantic reasoning, are illustrated in the following examples of complementarity in action.

Legal and judicial systems

For an example of using complementary forms of reasoning, consider the process of determining whether someone is guilty of a serious crime such as murder or manslaughter. This is carried out by a jury guided by a judge. It involves interpreting the meaning of rules. Both of the complementary aspects of reasoning, rule-based and meaning-based, come into play here and interact. This interaction is enabled by the formal structure of codified law, which contains exit pointsby referring to concepts such as ‘reasonable force’ whose meaning must be interpreted by the jury, guided by the judge. When examining raw evidence, thinking about the detailed aspects of evidence, studying the facial expressions of witnesses and accused, one is working in a world of meanings and uses, and one is guided by experience and intuition coloured by emotion. When considering the codified law and its implications, one is driven by reason and is following rules.

In almost all of the important aspects of daily decision making, we use both of these complementary types of reasoning to form conclusions. The great power and flexibility of an experienced person’s reasoning stems from the ease with which this pair of complementary systems work together, as we slip effortlessly from one to another and back again as required.

Works of art

Works of art are symbols, things to which an artist has ascribed function (that is meaning or use). When one is created, a function in the artist’s mind is projected onto facticities in the world (canvas, paper, stone…). A physical entity is created to express the artist’s grasp of beauty, their feelings of wonder, pathos, joy or amazement. Shape, colour, pattern, texture, size and detail are all used to express a vision, feeling or concept of beauty. When we look at a work of art, a reverse process takes place. We draw upon our emotional and cognitive capacities to ascribe function (meaning, understanding or appreciation) to the facticities before us (paintings, drawings, sculptures, etchings). We decode the symbolism that confronts us. From an initial bald facticity, and from our efforts to respond to it rationally and emotionally, we slowly learn to ascribe function to it. Such function, drawing on our personal and social experience, has to be reconciled to the facticity we see. All the basic processes involved – the artist’s mapping of function onto facticity and our reverse mapping endowing the facticity we confront with function, together with our final efforts to reconcile both activities are, to a greater or lesser degree, indeterminate. The complexity of the complementary thought processes involved in each person reaching a specific conclusion about any given work of art ensures that different people will necessarily reach different views, which reflect their different experiences. Any congruence of views saying that this particular thing is a great work of art is essentially a social consensus.

Complementarity of Realism and Idealism

When physicists first grappled with the paradoxes inherent in the behaviour of very small particles, they had great difficulty in coming to terms with the solutions proposed. Any experimental examination of small particle behaviour involves an exchange of energy. Looking at anything involves light being bounced off it. Light itself had been found to consist of small, energetic particles called photons. Difficulties in looking at very small particles stemmed from the impossibility of examining them without disturbing them. When something massive has light bounced off it, it is virtually unaffected. But when a photon hits an electron, the electron is deflected. The electron’s subsequent momentum had to be described by a wave of uncertainty. It took physicists a long time to switch from a particle or wave description to a particle and wave description. One famous physicist, when asked whether he believed in waves or particles, said that on Mondays, Wednesdays and Fridays he believed in particles, and on Tuesdays, Thursdays and Saturdays he believed in waves. On Sundays he tried to make his mind up. As someone deeply interested in philosophy, I had a similar trouble with reality. I’d go to bed a Realist and wake up an Idealist; only to change my mind a few days later. I longed for the certainty of a stable point of view. Eventually I realised that Realism (‘the physical world exists independent of minds’) and Idealism (‘the world is constructed only in minds’) were both compelling and equally useful descriptions of different aspects of experience. Using complementarity as an organizing principle harnesses both of these points of view into a coherent whole. If one seeks a philosophical label for this, it might be called a form of Pragmatism. Not, however, an anything-that-works-is-true approach, which is how the Realist and the Idealist both tend to caricature Pragmatism, but rather a way of coherently fusing different ways of thinking about our interactions with the world.

It seems to me that the price paid for allowing an inescapable indeterminacy into our descriptions of everyday life is worthwhile – it chimes with our experience. We do not live in a deterministic world, but in a world that is to an extent changed by, and dependent on, our interactions with it. Some topics of current philosophical interest, such as theories of Art and Artificial Intelligence, are illuminated by this approach.


There is an inescapable indeterminacy involved in the appreciation of art: one person might respond directly to colour and form, another might have a more emotional response triggered by childhood or other memories. This indeterminacy explains why there is such a wide spread of views in the theory and philosophy of art. One art critic recently wondered whether Art had lost the plot; from the point of view of complementarity, there is no plot. Our acknowledged great works of art are social constructions and represent no eternal truths.

Artificial intelligence

We have an evolved capacity to ascribe function (meaning and use) to facticity (perceived physical reality). As a logical concept, complementarity is fundamentally different from any of the concepts of classical logic, in a way reminiscent of the difference between classical and quantum physics. Classical logic underpins all design work on computers, robots and other forms of mechanical agency. In the present state of our scientific and technical knowledge, we simply do not know how to replicate the full range of ways in which human agency works. Our acquisition of function depends on learning. It evolves, in individually unique ways, as we grow up and grapple with the problems that the world sets us. We do not have a rule-book for living which we can design into a robot. What goes into the present day robot is a set of rules. Although we can give a sat-nav a human-like voice, endowing it with a semantic reasoning ability is a pipe dream. The fundamental indeterminacy that is an inescapable part of human agency may well be the rock on which current attempts to build robots with human levels of competence are foundering.

Two Cultures? Many Worlds? Three? Or One?

The late C.P. Snow made much of the existence of two cultures in our society, one science-based and one humanities-based. He seemed unaware that his own activities – a scientist turned novelist – constituted strong evidence against such a clear separation. Recent attempts to remove indeterminism from quantum mechanics, most notably Everett’s many-worlds theory, have sought to replace a world described in terms of probability by many worlds in which all possible deterministic outcomes are to be played out. Similarly, in his later years Karl Popper put forward the idea that we live in three separate worlds: the world of physical reality, the world of the self (one’s mind), and the world of social interaction via books etc. (culture). These he quaintly called Worlds One, Two and Three.

What is one to make of all this? Using an organizing principle like Complementarity helps us to avoid choices leading to such philosophical dead ends. Snow’s strictures are at best a plea for a broader form of secondary education. Everett’s ideas are a gift to science fiction. Popper leaves unclear how his three different worlds all fit together and interact. We live in one world, with different aspects. The big split is between facticity (what there is) and function (what we do with it). Complementarity can help us to a deeper understanding of the way in which material and immaterial aspects of our experience combine to form a broad representation of reality. The price paid is the admission of a fundamental indeterminacy into our descriptions of experience. Complementarity is not a form of dualism, but provides us with a broad, coherent description of all those aspects of reality which confront us in our daily lives.

© Sir Alistair MacFarlane 2010

Sir Alistair MacFarlane is a former Vice-President of the Royal Society and a retired university Vice-Chancellor.

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