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Now you see it, now you don't: what optical illusions tell us about our brains

Illusions can offer insights into how the visual system processes images.

Maurits Escher: where do the staircases lead?

The human brain is a network of about 20 billion neurons – nerve cells – linked by several trillion connections. Not to mention glial cells, which scientists used to think were inactive scaffolding, but increasingly view as an essential part of how the brain works. Our brains give us movement, language, senses, memories, consciousness and personality. We know a lot more about the brain than we used to, but it still seems far too complicated for human understanding.

Fortunately, the brain contains many small networks of neurons that carry out some specific function: vision, hearing, movement. It makes sense to tackle these simple modules first. Moreover, we have good mathematical models of nerve cell behaviour. In 1952, Alan Hodgkin and Andrew Huxley wrote down the “Hodgkin-Huxley equations” for the transmission of a nerve impulse, which won them the 1963 Nobel Prize in Medicine. We also have effective techniques for understanding small networks’ components and how they are linked.

Many of these simple networks occur in the visual system. We used to think that the eye was like a camera, taking a “snapshot” of the outside world that was stored in the brain like a photo stuck in an album. It uses a lens to focus an image on to the retina at the back of the eye, which functions a bit like a roll of film – or, in today’s digital cameras, a charge-coupled device, storing an image pixel by pixel. But we now know that when the retina sends information to the brain’s visual cortex, the similarity to a camera ends.

Although we get a strong impression that what we are seeing is “out there” in front of us, what determines that perception resides inside our own heads. The brain decomposes images into simple pieces, works out what they are, “labels” them with that information, and reassembles them. When we see three sheep and two pigs in a field, we “know” which bits are sheep, which are pigs, and how many of each there are. If you try to program a computer to do that, you quickly realise how tricky the process is. Only very recently have computers been able to distinguish between faces, let alone sheep and pigs.

Probing the brain’s detailed activity is difficult. Rapid progress is being made, but it still takes a huge effort to get reliable information. But when science cannot observe something directly, it infers it, working indirectly. An effective way to infer how something functions is to see what it does when it goes wrong. It may be hard to understand a bridge while it stays up, but you can learn a lot about strength of materials when it collapses.

The visual system can “go wrong” in several interesting ways. Hallucinogenic drugs can change how neurons behave, producing dramatic images such as spinning spirals, which originate not in the eye, but in the brain. Some images even cause the brain to misinterpret what it’s seeing without outside help. We call them optical illusions.

One of the earliest was discovered in Renaissance Italy in the 16th century. Giambattista della Porta was the middle of three surviving sons of a wealthy merchant nobleman who became secretary to the Holy Roman emperor Charles V. The father was an intellectual, and Giambattista grew up in a house in Naples that hosted innumerable mathematicians, scientists, poets and musicians. He became an outstanding polymath, with publications on secret codes (including writing on the inside of eggshells), physiology, botany, agriculture, engineering, and much else. He wrote more than 20 plays.

Della Porta was particularly interested in the science of light. He made definitive improvements to the camera obscura, a device that projects an image of the outside world into a darkened room; he claimed to have invented the telescope before Galileo, and very likely did. His De refractione optices of 1593 contained the first report of a curious optical effect. He arranged two books so that one was visible to one eye only and the other to the other eye. Instead of seeing a combination of the two images, he perceived them alternately. He discovered that he could select either image at will by consciously switching his attention. This phenomenon is known today as binocular rivalry.

Two other distinct but related effects are impossible figures and visual illusions. In rivalry, each image appears unambiguous, but the eyes are shown conflicting images. In the other two phenomena, both eyes see the same image, but in one case it doesn’t make sense, and in the other it makes sense but is ambiguous.

Impossible figures at first sight seem to be entirely normal, but depict things that cannot exist – such as Roger Shepard’s 1990 drawing of an elephant in which everything above the knees makes sense, and everything below the knees makes sense, but the two regions do not fit together correctly. The Dutch artist Maurits Escher made frequent use of this kind of visual quirk.

In 1832, the Swiss crystallographer Louis Necker invented his “Necker cube” illusion, a skeletal cube that seems to switch its orientation repeatedly. An 1892 issue of the humorous German magazine Fliegende Blätter contains a picture with the caption “Which animals are most like each other?” and the answer “Rabbit and duck”. In a 1915 issue of the American magazine Puck, the cartoonist Ely William Hill published “My wife and my mother-in-law”, based on an 1888 German postcard. The image can be seen either as a young lady looking back over her shoulder, or as an elderly woman facing forwards. Several of Salvador Dalí’s paintings include illusions; especially Slave Market With the Apparition of the Invisible Bust of Voltaire, where a number of figures and everyday objects, carefully arranged, combine to give the impression of the French writer’s face.

Illusions offer insights into how the visual system processes images. The first few stages are fairly well understood. The top layer in the visual cortex detects edges of objects and the direction in which they are pointing. This information is passed to lower layers, which detect places where the direction suddenly changes, such as corners. Eventually some region in the cortex detects that you are looking at a human face and that it belongs to Aunt Matilda. Other parts of the brain are alerted, and you belatedly remember that tomorrow is her birthday and hurry off to buy a present.

These things don’t happen by magic. They have a very definite rationale, and that’s where the mathematics comes in. The top layer of the visual cortex contains innumerable tiny stacks of nerve cells. Each stack is like a pile of pancakes, and each pancake is a network of neurons that is sensitive to edges that point in one specific direction: one o’clock, two o’clock and so on.

For simplicity, call this network a cell; it does no harm to think of it as a single neuron. Roughly speaking, the cell at the top of the stack senses edges at the one o’clock position, the next one down corresponds to the two o’clock angle, and so on. If one cell receives a suitable input signal, it “fires”, telling all the other cells in its stack: “I’ve seen a boundary in the five o’clock direction.” However, another cell in the same stack might disagree, claiming the direction is at seven o’clock. How to resolve this conflict?

Neurons are linked by two kinds of connection, excitatory and inhibitory. If a neuron activates an excitatory connection, those at the other end of it are more likely to fire themselves. An inhibitory connection makes them less likely to fire. The cortex uses inhibitory connections to reach a definite decision. When a cell fires, it sends inhibitory signals to all of the other cells in its stack. These signals compete for attention. If the five o’clock signal is stronger than the seven o’clock one, for instance, the seven o’clock one gets shut down. The cells in effect “vote” on which direction they are detecting and the winner takes all.

Many neuroscientists think that something very similar is going on in visual illusions and rivalry. Think of the duck and rabbit with two possible interpretations. Hugh R Wilson, a neuroscientist at the Centre for Vision Research at York University, Toronto, proposed the simplest model, one stack with just two cells. Rodica Curtu, a mathematician at the University of Iowa, John Rinzel, a biomathematician then at the National Institutes of Health, and several other scientists have analysed this model in more detail. The basic idea is that one cell fires if the picture looks like a duck, the other if it resembles a rabbit. Because of the inhibitory connections, the winner should take all. Except that, in this illusion, it doesn’t quite work, because the two choices are equally plausible. That’s what makes it an illusion. So both cells want to fire. But they can’t, because of those inhibitory connections. Yet neither can they both remain quiescent, because the incoming signals encourage them to fire.

One possibility is that random signals coming from elsewhere in the brain might introduce a bias of perception, so that one cell still wins. However, the mathematical model predicts that, even without such bias, the signals in both cells should oscillate from active to inactive and back again, each becoming active when the other is not. It’s as if the network is dithering: the two cells take turns to fire and the network perceives the image as a duck, then as a rabbit, and keeps switching from one to the other. Which is what happens in reality.

Generalising from this observation, Wilson proposed a similar type of network that can model decision-making in the brain – which political party to support, for instance. But now the network consists of several stacks. Maybe one stack represents immigration policy, another unemployment, a third financial regulation, and so on. Each stack consists of cells that “recognise” a distinct policy feature. So the financial regulation stack has cells that recognise state regulation by law, self-regulation by the industry, or free-market economics.

The overall political stance of any given political party is a choice of one cell from each stack – one policy decision on each issue. Each prospective voter has his or her preferences, and these might not match those of any particular party. If these choices are used as inputs to the network, it will identify the party that most closely fits what the voter prefers. That decision can then be passed to other areas of the brain. Some voters may find themselves in a state akin to a visual illusion, vacillating between Labour and Liberal Democrat, or Conservative and Ukip.

This idea is speculative and it is not intended to be a literal description of how we decide whom to vote for. It is a schematic outline of something more complex, involving many regions of the brain. However, it provides a simple and flexible model for decision-making by a neural network, and in particular it shows that simple networks can do the job quite well. Martin Golubitsky of the Mathematical Biosciences Institute at Ohio State University and Casey O Diekman of the University of Michigan wondered whether Wilson’s networks could be used to model more complex examples of rivalry and illusions. Crucially, the resulting models allow specific predictions about experiments that have not yet been performed, making the whole idea scientifically testable.

The first success of this approach helped to explain an experiment that had already been carried out, with puzzling results. When the brain reassembles the separate bits of an image, it is said to “bind” these pieces. Rivalry provides evidence that binding occurs, by making it go wrong. In a rivalry experiment carried out in 2006 by S W Hong and S K Shevell, the subject’s left eye is shown a horizontal grid of grey and pink lines while the right eye sees a vertical grid of grey and green lines. Many subjects perceive an alternation between the images, just as della Porta did with his books. But some see two different images alternating: pink and green vertical lines, and pink and green horizontal lines – images shown to neither eye. This effect is called colour misbinding; it tells us that the reassembly process has matched colour to grid direction incorrectly. It is as if della Porta had ended up seeing another book altogether.

Golubitsky and Diekman studied the simplest Wilson network corresponding to this experiment. It has two stacks: one for colour, one for grid direction. Each stack has two cells. In the “colour” stack one cell detects pink and the other green; in the “orientation” stack one cell detects vertical and the other horizontal. As usual, there are inhibitory connections within each stack to ensure a winner-takes-all decision.

Following Wilson’s general scheme, they also added excitatory connections between cells in distinct stacks, representing the combinations of colour and direction that occur in the two “learned” images – those actually presented to the two eyes. Then they used recent mathematical techniques to list the patterns that arise in such a network. They found two types of oscillatory pattern. One corresponds to alternation between the two learned images. The other corresponds precisely to alternation between the two images seen in colour misbinding.

Colour misbinding is therefore a natural feature of the dynamics of Wilson networks. Although the network is “set up” to detect the two learned images, its structure produces an unexpected side effect: two images that were not learned. The rivalry experiment reveals hints of the brain’s hidden wiring. The same techniques apply to many other experiments, including some that have not yet been performed. They lead to very specific predictions, including more circumstances in which subjects will observe patterns that were not presented to either eye.

Similar models also apply to illusions. However, the excitatory connections cannot be determined by the images shown to the two eyes, because both eyes see the same image. One suggestion is that the connections may be determined by what your visual system already “knows” about real objects.

Take the celebrated moving illusion called “the spinning dancer”. Some observers see the solid silhouette of a dancer spinning anticlockwise, others clockwise. Sometimes, the direction of spin seems to switch suddenly.

We know that the top half of a spinning dancer can spin either clockwise or anticlockwise. Ditto for the bottom half. In principle, if the top half spins one way but the bottom half spins the other way, you would see the same silhouette, as if both were moving together. When people are shown “the spinning dancer”, no one sees the halves moving independently. If the top half spins clockwise, so does the bottom half.

Why do our brains do this? We can model that information using a series of stacks that correspond to different parts of the dancer’s body. The brain’s prior knowledge sets up a set of excitatory connections between all cells that sense clockwise motion, and another set of excitatory connections between all “anticlockwise” cells. We can also add inhibitory connections between the “clockwise” and the “anticlockwise” cells. These connections collectively tell the network that all parts of the object being perceived must spin in the same direction at any instant. Our brains don’t allow for a “half and half” interpretation.

When we analyse this network mathematically, it turns out that the cells switch repeatedly between a state in which all clockwise cells are firing but the anticlockwise ones are quiescent, and a state in which all anticlockwise cells are firing but the clockwise ones are quiescent. The upshot is that we perceive the whole figure of the dancer switching directions. Similar networks provide sensible models for many other illusions, including some in which there are three different inputs.

These models provide a common framework for both rivalry and illusion, and they unify many experiments, explain otherwise puzzling results and make new predictions that can be tested. They also tell us that in principle the brain can carry out some apparently complex tasks using simple networks. (What it does in practice is probably different in detail, but could well follow the same general lines.)

This could help make sense of a real brain, as new experiments improve our ability to observe its “wiring diagram”. It might not be as ambitious as trying to model the whole thing on a computer, but modesty can be a virtue. Since simple networks behave in strange and unexpected ways, what incomprehensible quirks might a complicated network have?

Perhaps Dalí, and Escher, and the spinning dancer can help us find out. 

Ian Stewart is Emeritus Professor of Mathematics and Digital Media Fellow at the University of Warwick

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Bernie Sanders and the future of the American left

How an old, white guy is bringing class-based politics to the Democratic primary.

One thing is immediately striking: as he addresses primary rallies across America, arms flailing like a giant bird coming in to land, snow-white hair fizzing skywards like Doc Brown’s in Back to the Future, eyes startled behind the robust spectacles he has worn since childhood, Bernie Sanders looks quite unlike any other presidential candidate.

Perhaps the surprise in those eyes is sparked by the size of the crowds Sanders has been attracting. They are enormous, rivalling the numbers who turned out for Barack Obama back in 2008, and unprecedented for a candidate who is not shy of describing himself as a socialist: 28,000 in Portland and LA, 25,000 in Boston and 15,000 in Seattle. Even in Dallas, not a renowned centre of radicalism, 8,000 turned out to “feel the Bern”.

In these days when slick suits and expensive haircuts are increasingly a turn-off for a public weary of smooth politicians they see as delivering only for the wealthy, Sanders’s persona, like that of Jeremy Corbyn, his equally unkempt British counterpart, has proved popular. But it is his message – an angry chronicling of the depredations facing so many Americans and a solid social-democratic programme for putting things right – that is really pulling in the crowds. Sanders, who is 74, and the main challenger to Hillary Clinton for the Democratic nomination, doesn’t just look different. With his confident calls for a “revolution” to break up the banks and impose higher taxes on the rich, he doesn’t sound like any other recent presidential contender, either.


I first met Bernie Sanders in 1996. I was the publisher of his book Outsider in the House, a political autobiography that appeared the following year (and which has just been reissued by Verso with a new foreword, and more than a hint of optimism, as Outsider in the White House). The occasion was a benefit concert during his successful bid to be re-elected to the House of Representatives from the small, rural state of Vermont.

Sanders’s early years are not well documented, least of all by him. He devotes less than three of the 300 pages in Outsider to the first three decades of his life. He doesn’t much care for the “humble roots” narrative beloved of so many politicians, generally millionaires whose ancestors lived in broken-down cabins. But the raw material is certainly there. The son of Polish immigrants, Sanders grew up in a working-class Jewish family in Flatbush, Brooklyn. At home, money was tight: “Every major household purchase . . . would be accompanied by a fight between my parents as to whether we could afford it,” he wrote.

It was an achievement to gain admission to the University of Chicago, and though he described himself as “not a good student”, that was a result of sacrificing coursework to the cause of social activism. He settled permanently in Vermont at the age of 27, having bought an 85-acre farm in the north of the state for $2,500. Four years later he moved to Burlington, the state capital, where he became involved in city politics, at first in the tiny Liberty Union Party and then as an independent. In 1981 he was inaugurated as mayor and commenced a series of tilts at the state’s congressional seat. He finally entered the House of Representatives in 1991 – the first independent candidate to enter Congress in 40 years.

By the time I encountered him, Sanders was seeking to defend his seat for the third time. The concert where we met was taking place in an old art-deco theatre in Brattleboro, perhaps the most hippiefied community in a state where tie-dye remains as ubiquitous as dairy herds. It was headlined by Pete Seeger, who ran through a panoply from his folk songbook to a packed crowd that knew all the words.

Ten years earlier, Mayor Sanders, a long-time admirer of Seeger, had recorded one of his songs, “Where Have All the Flowers Gone”, on a surreal folk/rap album. Now, he waited until Seeger had finished his set before taking the stage and, speaking in the only manner he seems to know – a gruff, shouted staccato – exhorted Vermonters to join him in the fight against Newt Gingrich and Bob Dole to stop the Republicans from taking over the presidency and the Senate. The response was rapturous. Sanders left the stage like a president concluding a State of the Union speech, gladhanding lines of admirers as he made his way out of the hall.

A few weeks later I met him again, this time at his congressional office in Washington, DC. On the wall of his office I spotted a plaque of Eugene Debs, who ran for Congress and the presidency on a socialist ticket, travelling to every part of the country on a train he called the Red Special and picking up 6 per cent of the popular vote in 1912, when he finished fourth, behind Woodrow Wilson, Theodore Roosevelt and William Howard Taft.

Sanders had invited me to lunch and so we headed off through the underground passageway that leads from the office building to the congressional dining room. We were accompanied along the way by one of his assistants who, in true West Wing style, peppered him with questions and made notes on a clipboard as we walked. We had just started our food when John Kasich, then congressman for Ohio and now governor of the state and a contender for the Republican presidential nomination, wandered over for a chat. Despite Kasich’s reputation as a fiscal conservative, it was evident that he and Sanders had a cordial relationship, and indeed, Sanders invited him to join us for lunch.

It was difficult to reconcile these two contrasting snapshots of Sanders: the rousing air punch in Vermont and the bridge-building handshake in DC. But the more one looks into his career, the clearer it becomes that this dual approach is integral to his remarkable political ascent. Sanders plays it quite differently inside and out, but he plays both sides very hard.

“Bernie doesn’t see a contradiction between working within the system and campaigning to change it,” the journalist Matt Taibbi told me, recalling the time when he shadowed Sanders for several weeks in 2005 while researching a piece for Rolling Stone. “I remember one Thursday afternoon I made a snarky comment about members of the House already sneaking off home for a long weekend and how it seemed to me that many of them were pretty lazy. Bernie scolded me, insisting that most of the people in Congress work very conscientiously. He doesn’t believe the system functions for ordinary people, but he’s not cynical about it either.”

This point was reiterated by Heather Gautney, an associate professor of sociology at Fordham University in New York who previously worked as a researcher in Sanders’s Senate office. “Working with Bernie in DC, I realised what a difficult place it was for someone more interested in movement-building than passing legislation,” Gautney said. “But Bernie was known for getting substantial chunks of the Republican vote in Vermont and he used that same skill to connect with some pretty unlikely allies in Congress.”

Sanders’s legislative record is strikingly good. In the decade after the Republicans took over the House of Representatives in 1995 no other lawmaker attached more amendments to bills that were voted on. He achieved this by using his position as an independent to put together coalitions that spanned both of the main parties, and also by sheer hard work. In his Rolling Stone article, Taibbi describes Sanders waiting patiently for hours to table an amendment in the office of the House rules committee, “a tiny, airless closet deep in the labyrinth of the Capitol where some of the very meanest people on Earth spend their days cleaning democracy like a fish”.

Sanders’s method of working across party lines is not without its critics. Especially on the left, there are voices that wonder if the compromises that inevitably accompany playing the system in DC are too large. Many of Sanders’s positions on foreign policy have skewed towards the militarism and careless disregard for human rights that prevail among the Washington establishment. Although notably, and unlike Hillary Clinton, he opposed the initial vote on the Iraq War, Sanders voted for every bill that came before Congress to fund the occupations of Afghanistan and Iraq. He has supported basing the new F-35 fighter plane at Burlington Airport in Vermont, despite widespread concern from residents about the environmental impact. And he did not oppose the Senate resolution that supported Israel’s attack on Gaza in 2014, which left as many as 2,200 Palestinians dead.

Sanders is clearly happier talking about problems inside the US than foreign policy. In his opening statement to last Saturday’s televised debate between the Democratic candidates, he segued awkwardly from condemning the attacks in Paris to excoriating America’s “rigged economy”. Yet on domestic issues, too, some of his stands have given progressives pause for thought: his opposition to the Trans-Pacific Partnership, a 12-country trade agreement championed by Barack Obama, has always been grounded in an argument in favour of saving jobs for American workers, rather than any notion of international solidarity. His slowness in expressing support for the burgeoning Black Lives Matter movement, something which his campaign has latterly striven hard to correct, was less of a surprise to those aware of his consistent support for the police union while mayor of Burlington. And his position on guns (he voted against the Brady Bill, which mandated background checks on buyers of firearms) is the only area in which Clinton outflanks him to the left.

But perhaps the biggest issue for many progressives is Sanders’s decision to run for president through, rather than outside, the Democratic primary. Though he began his political career in the Liberty Union Party and has stood in every election since as an independent, he is, as Howard Dean, the progressives’ challenger in the Democratic primary of 2003/2004, put it, “basically . . . a Democrat . . . [who] votes with the Democrats 98 per cent of the time”.

As Sanders relates in Outsider in the House, faced in 1996 with the choice of backing Ralph Nader, “a personal friend and an exemplary progressive” running as an independent, or Bill Clinton, whose policies on health care, welfare reform, trade, gay marriage and military spending he sharply disagreed with, Sanders decided to “support” Clinton. “Perhaps ‘support’ is too strong a word,” he frets in the book. “I’m planning no press conferences to push his candidacy, and will do no campaigning for him. I will vote for him, and make that public.”

Sanders has called for a vote for the Democratic nominee in every presidential election since Jimmy Carter left office in 1981, and early this month, on ABC’s This Week, he appeared to have completed a long transition, asserting: “I am a Democrat now.”

This failure to build an electoral force outside the Democrats always leads to a dead end, according to Anthony Arnove, a prominent member of the International Socialist Organisation (ISO) who is also a publisher and literary agent representing a range of leftish writers, including Arundhati Roy. “We’ve seen it over and over,” Arnove said: “a left challenge fires up the base and is then defeated in the primaries by a centrist, or, more accurately, right-wing candidate, who goes on to betray everything those people were mobilised around.”

Sanders’s fundraising almost matched Clinton’s over the summer – in the third quarter they raised $26m and $28m, respectively – and in September he became the first candidate to attract more than a million individual donations. (The average donation to his campaign has been $30.) But his dip in the polls after Hillary’s strong performances in the first nationally televised primary debate, and then again at her House select committee hearing on the 2012 attack on the US consulate in Benghazi, Libya, suggests he will struggle to win the nomination. As of early November he trailed Clinton nationally by 25 points.

In Arnove’s view, Sanders “won’t get further than Super Tuesday [at the beginning of March], when he’ll direct his base to vote for Clinton. This is exactly how the Democrats become a graveyard for progressive politics, when what we desperately need are social movements that can remain independent of both establishment parties and push for their own agenda.”


The revolution to which Sanders often refers is a long way from the sort envisaged by Arnove’s ISO. He is pursuing a fairer capitalism, not its overthrow. “He’s not Trotsky,” as Taibbi put it to me. But there are those inside his campaign who think its primary focus should be building a grass-roots organisation capable of transcending the four-yearly coming together of presidential elections, to create a more permanent basis for a broad, progressive movement.

One such advocate is Adolph Reed, a writer and academic who is campaigning for Sanders in South Carolina. Working with local unions and Labor for Bernie Sanders 2016, which has 70,000 signed-up members, Reed sees the potential in using Sanders’s programme, with its emphasis on basic economic demands such as the minimum wage, universal health care and free college tuition, as a way of drawing together various groups campaigning around single issues such as housing and police racism.

For Reed, who is black, class trumps race as the key to building a movement. “In New Orleans everyone talked about Katrina as having a devastating effect on black people in the city, which of course it did. But when you analyse it, class was a much better predictor of who suffered most there,” he told me. The centre of a class-based movement, Reed argues, will have to be provided by the trade unions. “Despite the fashionability of protests without any specific demands or elected leaderships, no movement initiative is going to have staying power without being anchored in the trade unions.”

Recruiting the unions to work alongside Sanders’s campaign in the way Reed envisages isn’t easy. The American Federation of Teachers and the machinists’ union have already thrown in their lot with Hillary Clinton. And Richard Trumka, the president of the AFL-CIO (America’s national federation of trade unions), has warned individual unions against coming out for Sanders. But Reed can point to significant declarations of support, from postal workers and the National Nurses Union. The AFL-CIO chapters in Vermont and, more surprisingly, South Carolina have also backed his run.

“It’s important to keep Bernie in the race for as long as possible, but the ultimate objective is to develop structures that can continue beyond the election,” Reed said. “It’s premature to say what this network will look like, but Bernie’s campaign provides an important boost to putting it in place.”


From Jesse Jackson to Dennis Kuci­nich to Howard Dean, an array of people’s champions has made a splash in the recent history of Democratic presidential primaries. None, however, has been as explicitly critical of capitalism (or so gruff about it) as Bernie Sanders. His no-nonsense, class-based politics are a measure of how the disenchantment with the ideology of a free market that arrived like a train in the 1980s and ran off the rails in 2008 is now finding its way into the mainstream.

Up until now, the critical moments of left advance in America – the Seattle WTO protests, the anti-war movement, Occupy Wall Street, the campaign for gay rights and, today, Black Lives Matter – have occurred outside electoral politics. There are a couple of good reasons for this. The US electoral system, like Britain’s, makes third-party challenges extraordinarily difficult. And inside the Democratic Party these movements would have been crushed by a conservative leadership around the Democratic National Committee, put in place by Bill Clinton.

One result is a paucity of new progressive voices inside the party. At a moment when, as Gramsci once put it, the old order no longer works but the new order has not yet been born, Sanders, with his New Deal politics and firebrand demeanour, seems not so much a successor to the old order as a throwback to a time that pre-dates it, when politicians spoke with conviction and the society they represented was less unfair. As such, he provides a staging post for a new progressive consciousness (according to a poll by Pew at the end of 2011, more Americans aged 18 to 29 would prefer to live under socialism than under capitalism) that is not yet sufficiently coherent to enter mainstream politics in its own right, either through a serious third-party challenge or the transformation of the Democratic Party.

As a middle-class white man, Sanders has been able to get a pass to promote bold positions that someone with a less privileged identity might have found hard to sell. And his age, paradoxically, has proved not to be a disadvantage with a youthful constituency dismayed by the surrender to expedience that disfigures so much of contemporary American politics. His record has been constant over such a long period that, again like Jeremy Corbyn, he can be relied on not to sell out. Though his politics are less radical, his venerability provides a messianic cloak from the same closet as the one worn by Noam Chomsky, another hero for many young progressives.

So it’s not just today’s professionally polished politicians to whom Sanders presents a stark contrast. Recent progressive movements have embraced an identity politics that was much less prevalent when Sanders started out back in 1970s Vermont. In order to forge the sorts of alliances that are necessary to mount a credible challenge on the national political stage, they will likely have to borrow extensively from his unifying class politics. But their leadership will be younger, blacker, less straight and less masculine than Sanders. In that sense, he represents the last hurrah for the old white guy.

Colin Robinson is co-publisher at OR Books (, based in New York

This article first appeared in the 19 November 2015 issue of the New Statesman, The age of terror