The recent revival of interest in The Frankfurt School deserves some thought. The first point to make is that it isn't really being revived, having never actually gone out of fashion, despite clumsy attempts on the right to recast it as the covert and marginal conspiracy of "cultural Marxism" (deliciously parodied in the Coen brothers' Hail, Caesar!, which went meta when critics lamented the lack of a plot despite the centrality of a gigantic plot). The Frankfurt School's persistence reflects its ambition. It sought to synthesise positivist and idealist strands in philosophy with an explicit focus on the institutions and cultural artefacts of modern capitalism: what became known as Critical Theory. In other words, it was vast in scope, employed popular critical tools, from psychoanalysis to the deconstruction of commodities, and was sufficiently non-dogmatic and sceptical to provide bed and board for many lodgers, from Walter Benjamin to Frederic Jameson. The overlaps with both modernism and postmodernism mean that we could legitimately describe it as a theory of the Western twentieth century.
As an approach to sociology and politics it had an enormous influence on the counterculture of the late-60s and early-70s, from "admass" to environmentalism. Along with the rediscovery of Antonio Gramsci, it was an important factor in the euro-communist and post-Fordist shift of the left in the 70s and 80s (notably the "retreat from class" critiqued by Ellen Meiksins Wood). Since the 80s, it has provided invaluable insights in the study of neoliberalism, particularly in respect of the marketisation of institutions and the intersection of politics and media. Even before it lost its capitalisation and became simply shorthand for modern thought, Critical Theory was so capacious a subject as to make it difficult to fully define, but there are three characteristics that are worth highlighting with regard to its current modishness: pessimism about the revolutionary potential of the working class; the importance of communication and thus media to rationality, which lives on in Jurgen Habermas's emphasis on the public sphere; and the concept of instrumental reason detailed by Max Horkheimer in Eclipse of Reason.
Some of the fresh interest can be explained by 2008 and the end of "the end of history". This is partly a desire to pick up the thread of a historically situated theory of politics, which also prompted the brief resurgence of interest in Marx, but it also owes much to the "black swan" shock of the global financial crisis. This didn't just damage the reputation of economics in practice (and point up the absurdity of its physics-envy), it also called into question its normative theory, notably the emphasis on quantification and utility - i.e. the notion of aggregate good based on a common, mathematical scale of happiness that starts with Bentham's "felicific calculus". While the narrow definition of reality as that which can be calculated lives on, not least among our tech overlords, the contemporary popular mood is open to the idea of a wider, more humane reality, including the recognition that reason may be biased by interests, e.g. the fashion for behavioural economics, and the yearning for eternal verities, e.g. the fashion for pop-philosophy.
These two examples reflect respectively the concepts of subjective (i.e. self-interested) reason and objective (i.e. timeless) reason, which Horkheimer contrasted to instrumental reason. The latter, which becomes hegemonic with the Enlightenment, seeks domination over nature and the self, thereby producing capitalism, self-repression and ultimately Fascism (Horkheimer was writing in the mid-40s). In its relegation of the ethical basis of goals ("what is good?") in favour of the efficiency of means ("what works?"), instrumental reason builds on Max Weber's concept of rationality to provide an acute critique of the unregulated markets and managerialism of neoliberalism avant la lettre. The idea was placed in a historical context by Horkheimer and Theodore Adorno in Dialectic of Enlightenment: "Myth is already enlightenment, and enlightenment reverts to mythology". The point of this apercu is not just that there wasn't a sudden jump from one stage of history to another, i.e. from a world of myth to one of science, but that modern rationality inescapably contains its own irrationality just as ancient superstition was often rational.
This irrationality is not a remnant of the past but the newly-minted product of progress, leading to Adorno and Horkheimer's pessimistic conclusion that we face the inevitable "regression of reason". While there is an obvious conservative timbre to this (and you can clearly see its influence on the work of John Gray et al), it also serves a liberal purpose in allowing the idea of progress to be preserved as a possibility while setbacks, such as the UK's EU referendum result and the US election of Trump, can be treated as temporary spasms of irrationality. Less is heard today of Horkheimer's belief that solidarity through suffering is the key to human emancipation, essentially because modern liberal solidarity is primarily a financial transaction, whether in the form of debates about an extra penny in tax for the NHS or the calls for donations to charity. The focus is not the need for collective action, but the need for the collective support of liberal gatekeepers who can address occasional market failures.
The Frankfurt School's scepticism towards Marxist teleology and its disillusion with the proletariat long ago made it acceptable to the liberal establishment. During the 1980s and 90s, its emphasis on the construction of rationality through communication (Habermas's "dialogic democracy") fed into the notion of a "stakeholder society" organised around the "vital centre" and reinforced the self-regard of liberal commentators as the dominant facilitators of public conversation in the golden era between the fall of the Berlin Wall and the arrival of the Web. Starting in the 00s, as the tech companies began to eat their lunch, traditional liberal media rediscovered the value of the Frankfurt School's critique of commodity capitalism's corruption of the public sphere. Now, with the supposed tidal surge of "fake news", the concept of instrumental reason provides a ready-made buttress for think-pieces decrying our collapse into unreality and anger.
Much of the instrumental revival of the Frankfurt School is simply a beef about the shifting power of media ownership. In The New Yorker in December, Alex Ross made this explicit: "From the start, Silicon Valley monopolies have taken a hands-off, ideologically vacant attitude toward the upwelling of ugliness on the Internet. A defining moment was the turn-of-the-century wave of music piracy, which did lasting damage to the idea of intellectual property. Fake news is an extension of the same phenomenon, and, as in the Napster era, no one is taking responsibility. Traffic trumps ethics". Given that "fake news" is a monetisable commodity, the equivalence with file-sharing, which temporarily de-commoditised music (and has now been superseded by the monetisable commodity of streaming), is absurd. Ross opens his piece with an image of a house (Thomas Mann's villa in Los Angeles) saved from destruction, which simply reinforces the suspicion that this is about the preservation of certain forms of capital and intellectual property, not the search for truth.
The Frankfurt School offers a fruitful source of critical theory that can be repurposed to serve liberal interests, which is ironic given the originators' scepticism about liberal society. The idea of the "regression of reason" offers a convenient (if misleading) equivalence of modern politics with Weimar Germany. The importance of communication to rationality gives a heroic role to the media as guardians of the public sphere, and a way of characterising new media as a mix of instrumental stupidity ("Traffic trumps ethics") and the malign exploitation of base human instincts (Trump traffic). Inevitably, there is a degree of compensation going on here, with tributes to the prescience of the Frankfurt School allowing outlets like The Guardian and The New Yorker to increasingly rely on conservative rhetoric in their defence of the old media dispensation. What is unchanged in this worldview is that the working class remains resolutely off-stage, incapable of acting as the motor of progress and prey to the easy charm of demagogues.