And so to part the fourth. The previous three parts of Jonathan Israel’s attempt to rewrite the history of the Enlightenment ran to the thick end of 3,000 pages. Now here we have another thousand pages of impressive, dense, defensive, tetchy certainty. Crying in the wilderness has never seemed attractive to Professor Israel. Sick of locusts and never given to honey, he storms into the centre of historiographical controversy, twirling round and round and carving a space for himself — a very wide space — with his machete.

He is a very talented man. But it takes something closer to genius, fuelled with pertinacity, to say essentially the same thing for a quarter of a century across 4,000 pages of argument. What those pages say, helpfully condensed, is that he was right all along.

Cognoscenti will begin at page 923 where they will be told (again) why the “Radical Enlightenment Thesis” (again) needs defending (again). Here is a beginner’s guide for those who have so far avoided these mysteries.

Israel believes that we should speak not of one Enlightenment but two. One of them readers will recognise: it is French, with some assistance from the Scots. It takes off in the 1730s and ’40s and has its champions in famous names Montesquieu, Voltaire and Rousseau. It ends with the disaster of the French Revolution, the coming of monster Robespierre and the ascendency of Napoleon. This is the “Moderate Enlightenment” Israel is addicted to capital letters and it is characterised by its unwillingness to break away from reactionary aristocracy and its accomplice, the Church.

There exists another enlightenment placed before his public by Professor Israel. It began earlier and lasted later; it did not begin in France but in what we now call the Netherlands; its founding fathers fraternised in a cercle spinoziste inflamed by the monism and atheism of their Jewish prophet. They established a “stream”, a “strand”, a “tendency”, whose names may be less celebrated — d’Holbach, Condorcet, Raynal, Destutt de Tracy — but they carried forward the possibility of real rather than bogus Enlightenment by dispelling moderation, timidity and confusion. They promoted what Israel has consistently called the “Radical Enlightenment”, one committed to representative democracy combined with hostility to religion and superstition.

These two streams are supposed to coexist, one flowing openly, the other often driven below ground by the repression of its opponents. No prizes for guessing which stream strikes Israel as the more significant and worthwhile. Gazing out of his window in Princeton, our author sees only Trumpian America with all the promise of the American and French Revolutions betrayed and sullied. If only people had listened to Spinoza … What should have been the Radical Enlightenment became the failure of the Moderate Enlightenment with its smelly compromises. It failed progress and justice and social equality. It failed democracy. It failed modernity. More culpably, it failed Professor Israel.

He has, notwithstanding this depressing outcome, introduced some important and memorable contentions into our thinking about the Enlightenment. First, perhaps most significantly, he has decentred an anglophone concentration in the literature, a task urgently required here as elsewhere in Western intellectual history. Israel is a formidable linguist, not merely in the knowledge of Dutch and German manifested in his earlier work, but also of Latin, French, Italian, Spanish and the Scandinavian languages which he quotes in the original.

Israel believes that we should speak not of one Enlightenment but two

Second, he has disturbed both the chronology and the spatial frame of discussion. His insistence on pushing Enlightenment attitudes back to the late seventeenth century and his less successful determination to press it forwards into the 1840s extends the narrative in challenging ways, just as his willingness to involve the American Revolution and South American liberation as features of the Enlightenment that have often been seen in purely “European” terms, lends a fresh, if not always persuasive, perspective.

That said, one should report that many scholars of the subject, much the majority, have rejected the entire project of a discrete and coherent “Radical Enlightenment”; they now stand in the dock as proponents of what Israel calls “the Negative Critique”. What they are negative about varies. Sometimes it turns on proportionality. Are these two “streams” even remotely comparable in their consequences? Perhaps we are placing the expansive Rhône against one of those tributary rivulets that wind their way unnoticed across the French countryside. Are they streams at all?

One might want to see radicalism and moderation as merely points on a spectrum of belief rather than contested, hermetic ideologies. Then there is Israel’s repeated assertion that intellectual “vanguards” represent the central causal elements in wider political and social developments and especially that “an elite of radical enlighteners” directed eighteenth-century insurrection. One wonders whether this form of self-flattery may call to mind Graham Wallas’s observations about “the intellectual fallacy”: the view held by intellectuals that intellectuals are important and that their perception of politics, normally located somewhere between the bien-pensant and the myopic, should be deemed cutting edge in their acuity.

Or is the entire discussion of “Radical Enlightenment” burdened less by a failure of imagination than a failure in expectation? It does not seem unreasonable to ask whether the requirement of this collection of demands, many of which will have struck contemporaries as insane, flies in the face of every cultural constraint familiar to the eighteenth century, a fortiori when its champions were hardly names to place alongside the celebrated personalities doomed to “Moderation”.

Rarely, after all, have Voltaire and Rousseau undergone so savage a diminution as they suffer in these pages. Never have d’Holbach and Destutt de Tracy discovered so momentous a resurrection. People may be forgiven for suspecting that someone, somewhere is trying a little too hard.

One has to admire the determination which Israel brings to the defence of his position in this final volume of the series; and he is right to imply that some of the criticism that he ha s faced tends towards small-mindedness. In the face of 4,000 pages, he merits a more sophisticated seam of criticism. One part of that seam concerns method. A second, deeper, asks how intellectual history should proceed in the twenty-first century.

Picture Professor Israel at his desk with an “In” tray and an “Out” tray. All the quotations from his sources that suggest a “Radical Enlightener” go into “In”; all those betraying a “Moderate” are “Out”. The problem does not lie in his decision about which tray. It resides in the trays themselves as harbingers of historical understanding and leaves sceptics dreaming about many trays, trays that change over time, trays that shrink and expand. They may ask, more fundamentally, what the point of such trays is, anyway.

Observers of his separations and compartments may indeed make a decision of their own: that Israel is not really an historian at all so much as a teleological taxonomist. Teleological, because he thinks backwards from a desired present to identify the roots of its undoing. Taxonomist, because he believes that isolating his ideal types provides some sort of precondition for understanding when it may in fact obstruct historical sensitivities.

One suspects, and his acknowledgments confirm, that Israel has been talking to philosophers: a regrettable procedure since they never see the point of historicisation — it blurs the edges of their conceptual categories. But morphology is what historians do. Israel’s method promotes continuities contained in terms such as “tradition”, “tendency”, “echo” and “legacy” and arguably renders trans-temporal what may in reality have been evanescent. Indeed, there are moments when one wonders why Quentin Skinner or Reinhart Koselleck ever bothered putting pen to paper. But then, a certain pre-1960 atmosphere hovers over the approach here, recalling the founder of intellectual history as a genre, Arthur Lovejoy, and his “unit-ideas”. Israel’s idea is not a unit but a molecule containing democracy and atheism but it behaves in a similar way in its permanence, its almost tactile quality. He concedes that it alters “according to different circumstances” but that is a way of conceding ground without surrendering any. Shorn of its definite article, “Radical Enlightenment” jumps from his writing pad and becomes a thing-in-the-world, running about and shoving along its adherents. “Radical Enlightenment had pushed in this direction”; “Late Radical Enlightenment edged forward”. What began as a taxonomic device turns into a rather alarming ontological presence.

Consistent with his understanding of the past as an observable domain, Israel is committed to “historical accuracy” a favourite phrase which is coextensive with what “the” evidence “proves” (meaning what his chosen evidence renders plausible). But people refuse to see it. They “could not be more mistaken”; they belong to a “wrong-headed historiographical tradition”; they repeat an “utterly false myth” [sic]; they say things that are “wildly fallacious and utterly misleading”. This is Israel in polite mode.

Raise the “Postmodernists”, though, another reification in capitals, and he ignites in baffled fury against their “enfeebling, ultimately absurd” contentions about the place of language and its shifting referents. (It is a truth universally unacknowledged that the historians who rail most hysterically against postmodernism are those who never understood its claims in the first place.) Deaf to such distractions, Israel needs to be right because it is possible to be right. He stamps his foot in italics. It “was meant to be democratic”. He “was a revolutionary”. Professor Israel has spoken.

He has spoken and he has written and, with the completion of his project, there they all are: 4,000 pages of argument and contestation. Any fool can criticise such an achievement; it would require a scholar of Israel’s acumen to repeat it, let alone rival it. He has not won the argument but will undoubtedly die believing that he has, which is nearly as satisfying. A quarter of a century’s efforts deserve more than denigration in any case and the time has come for a commission on reconciliation. Passing through Princeton, if you do, buy the man a drink and be nice.

Just don’t mention the Enlightenment.