Until his welcome intervention on Monday afternoon, the debate over Labour and anti-semitism, which has been rumbling on since Jeremy Corbyn’s leadership victory in 2015, seemed to have reached a tipping point. There has been widespread revulsion at Corbyn’s defence of a virulently anti-semitic graffiti artist, and contempt for his excuses for doing so: that he was merely defending the right to free speech and had, unfortunately, failed to examine the picture closely enough.

When the Jewish Chronicle first raised the issue of Corbyn’s support for Mear One’s astonishingly crude depiction of a cabal of “Jewish” financiers in November 2015, Corbyn’s supporters accused the paper of manufacturing a politically-motivated anti-Semitism scandal in order to “smear” his good name. At that time, the story did not even merit a response from the Labour leadership. This time it caught fire, perhaps due to it swiftly following evidence of Corbyn’s active participation in an anti-Zionist Facebook group which regularly hosted Holocaust denial and viciously anti-semitic conspiracy theories.

A substantial section of Corbyn’s support has continued to claim that the story of the mural is merely another example of the “mood music” – to quote Unite chief Len McCluskey - generated by the pro-Israel right of the party as a cynical means to undermine Corbyn’s leadership, just in time for the May council elections. But the smarter wings of the Corbyn project have grasped that the evidence of his support for Mear One is so damning, and the fumbling response so clearly deceitful, that reflexive accusations of a concocted “smear” no longer hold water.

Their alternative response has come in three interrelated forms. First, Corbyn’s anti-semitism – and by extension, that of the left more generally – is denied on the grounds that someone who has spent his life opposing “all forms of racism” could not possibly be receptive to anti-semitic representations of the world. Corbyn’s track record of anti-racist activism - most famously his opposition to South African apartheid - precludes him from trading in or tacitly supporting anti-semitic forms of thought or action. Therefore, if on this occasion, he had inadvertently failed to recognise what was a clearly anti-semitic image, this must have been a momentary aberration, an unfortunate mistake, the gravity of which is far outweighed by his otherwise flawless history of anti-racism.

This leads to the second response. Expressions of anti-semitism on the left are dismissed as aberrations from the norm. Corbyn suggested in his statement on Sunday that, whilst anti-semitism sadly does exist within “pockets” of the party, they are not at all representative of the whole. The removal of these pockets would therefore annul the problem. The widespread portrayal of anti-semitism as a “virus” or “disease” on the left exemplifies this response. It is seen as something completely alien and incompatible with a leftist worldview, something which therefore invades the left from the outside. As such, its origins do not require serious consideration, rather its effects combated.

Third, incidences of anti-semitism are diminished with reference to examples of anti-semitism on the right. Witness, for instance, former Labour MP Chris Mullin’s assertion that anti-semitism is a societal issue of which Labour’s problem is only one part, and as such the significance of its left variant is vastly over-exaggerated by a media out to score easy hits on Corbyn.

Mounting an effective challenge to this portrayal of leftist anti-semitism as merely an unfortunate error or a minor problem requires more than blanket accusations of racism. Doing so merely replicates the superficial analysis which explains anti-semitism as an inexplicable “disease” generated by the innate character of “bad’ people. It fails to grapple with the real contradiction inherent in a situation whereby individuals and groups who otherwise attest to a belief in equality and solidarity among peoples regardless of race could at the same time indulge remarkably frequent and increasingly confident expressions of anti-semitism.

A coherent explanation is required to combat and convince those whose concern is to protect the Corbyn project from what they incorrectly see as a smear campaign of little real-world consequence. And it must be an explanation that emerges from the specific character of the Corbyn worldview itself, the particular form of the critique of contemporary capitalism espoused by Corbyn and his supporters, rather than one imposed upon it from the outside.

Indeed, it was Corbyn himself, when he finally offered a thorough and sincere statement on the matter on Monday afternoon, who best captured what is at stake here. There was a seriousness in the statement lacking in his previous attempts to address the issue. The “few bad apples” theory was definitively dispatched with, and Corbyn drew a direct link between left anti-semitism and the “socialism of fools” based around “the old anti-semitic conspiracy” that depicts “Jewish bankers and capitalists exploiting the workers of the world”. This begins to get to grips with deep-seated theoretical underpinnings of left critiques of capitalism that have anti-semitism as their logical consequence.

If words lead to action, this represents a significant leap that may well bear compromises in how Corbyn characterises his political mission. Just how much of Corbynism’s own conceptualisation of capitalism must change in order to render it resistant to appropriation in the service of anti-semitic conspiracy theories of capitalism? To answer this, we might turn towards the work of a recently-passed Marxian critical theorist largely unencountered in the mainstream UK left.

Last week, the left lost a vital light leading the way out of the impasses of left anti-semitism. Moishe Postone was a Canadian academic famous for his trenchant critique of the affinities between forms of anti-capitalism and anti-semitic conspiracy theory. This critique has wielded tremendous impact on the German left in particular, but in the UK its lessons have been sadly neglected.

Postone’s analysis begins by making a distinction between anti-semitism and “other forms of racism,” one which Corbyn has notoriously found difficult to express. Plenty of other racial and ethnic groups are despised. But, Postone suggested, it is only Jews who are suspected of secretly controlling the world. A mural of Mexican migrants or black people counting money on the backs of the oppressed would make no sense to a racist. But the portrayal of Jews at the table could escape Corbyn’s scrutiny because this representation of how power works resonates with the logic of his worldview: his understanding of capitalism as a “rigged system”.

As he routinely argues, the problems in British society, and capitalist society more generally, can be explained by the conscious actions of a parasitical “1 per cent” draining the vitality from the “real economy.” This “global elite” do not produce anything tangible but merely make money out of money through their control of the banks and the international financial system. They are thus regarded as an irrational excrescence undermining what would otherwise be a rationally ordered, naturally benevolent productive society.

The implication of Corbyn’s condemnation of those who have “stitched up” the political and economic system “to line the pockets of their friends” is that if only this unproductive excess could be somehow removed, “socialism” would appear, as if by magic. The task of a political movement is, therefore, to identify the guilty parties held to be personally responsible for the current malaise, and to remove them from the organic community of the productive.

This kind of productivist worldview did not originate with Corbynism. Indeed, his rise is more a result of its revival than its cause. It was widespread amongst the Occupy movement, and can also be found in various forms amongst the hard right, including the Leave campaign and Donald Trump – from whom Corbyn borrowed the “rigged system” conceit. A recent story in the Daily Telegraph about George Soros’s supposed “secret plot to thwart Brexit” is a case in point.

The roots of such “personalised critiques” of capitalism can be traced back to vulgar understandings of Marx’s so-called “labour theory of value” – understandings which it was Postone’s life’s work to overturn. They do not necessarily have to lead to anti-semitism, but it does not take much for the search for those “rigging the system” to alight on the “rootless ‘cosmopolitan” Jew, forever holding the productive community to ransom though his control of the financial system.

The same pattern is found on a geopolitical level when it comes to Israel. The inordinate focus on the crimes of Israel within the British left – far outweighing the attention given to the chemical slaughter currently inflicted by Bashar al-Assad for example – results from the portrayal of Israel as the evil “1 per cent” of the global community, a state whose very existence is the source of all suffering in the Middle East, if not the world.

Postone’s alternative reading of Marx shows us that a critique of capitalism which focuses only on the machinations of the “1 per cent” fails to understand how fundamentally capitalist social relations shape the way in which we live – capitalists and bankers included. It does not grasp the extent to which “real” industrious production and intangible “abstract” finance are inextricably entwined. The pursuit of profit is not a choice in capitalism, but a compulsion. Failing to do so leads to bankruptcy, starvation and death. Nor are banks and the international financial sector an unproductive parasitical outgrowth undermining the vitality of the “real” national economy. They are that economy’s precondition.

The results of this incessant pursuit of profit, facilitated by the global movement of money, are by no means equal, and to that extent Corbyn and his supporters are right to highlight the widespread economic disparities in society. Indeed, the danger of conspiratorial thinking on the left is that it does in some ways “reflect a critical impulse”, a suspicion about the world and its forms of power.

It is also why, as the sociologist David Hirsh has argued, anti-semitism can present itself as a progressive and emancipatory force, a valiant attempt to rid the world of the evils dragging it down. It replicates the way that anti-migrant racism has become a sign of one’s commitment to a downtrodden “white working class” in the aftermath of Brexit.

Therefore to dismiss the existence of anti-semitism on the left as a minor problem compared with that of the right is to fail to heed the risks that the two forms can, on occasion, complement each other. A critique of capitalism based on the need to eradicate “globalism” is politically ambiguous at best, able to be utilised by the far-right as easily as the left.

What this lapse from critical to conspiracy theory suggests is that the anti-semitic tropes which pervade the Corbyn-supporting “alt-media” and activist base, as well as Corbyn’s own dubious brand of “anti-Zionism” and “anti-imperialism”, are not mere contingencies, but the logical outcome of the movement’s morally-charged, personalised critique of capitalism as conspiracy.

This has implications for how Labour addresses the current crisis. The specificity of left anti-semitism arises partly from a foreshortened critical impulse imbued with a racism that punches upward, rather than down. Building an alternative therefore requires much more than expulsions of “pockets” within the Labour Party.

What is needed is a commitment to education and consciousness-raising capable of replacing bad critiques with good - and Corbyn showed yesterday that he might be prepared to lead from the front. The work of Postone would be an excellent place to begin. What it shows is that, if Corbyn is as serious as he says he is about militant opposition to anti-semitism, his worldview as it is may not survive intact. Rather, it must be radically revised and rethought.

Matt Bolton and Frederick Harry Pitts are the authors of Corbynism: A Critique of the New British Left, forthcoming with Emerald later this year