Ideas matter. Indeed, as J. M. Keynes observed, “the world is ruled by little else”. Especially, alas, when they are bad ideas. For the influence of ideas bears no relationship either to their utility or to their truthfulness. Rather the contrary: it’s almost as though there is a Gresham’s Law of ideas, in which bad ideas drive out good.

This is the first of a series about such bad ideas. It will identify their origins and their consequences. And, above all, it will try to show how they can be put right — usually by good history.

I begin with one of the worst and therefore one of the most influential: the Separation of Powers. Like most bad ideas, it comes from France. Its author was the philosophe and jurist Charles-Louis de Secondat, Baron de Montesquieu. His Spirit of the Laws divides the powers of the state into three (the so-called trias politica or “political triad”) — the legislative, the executive and the judicial — and argues that freedom and good government depend on the separation and mutual independence of the three.

This doctrine — which, like much eighteenth-century French thought, has the superficial attractions of neatness and apparent symmetry — has proved irresistible to the long line of leftish politicians and would-be reformers who have tinkered with the British constitution in the last 15 or 20 years.

The Separation of Powers provided the rationale for the demotion and intended abolition of the post of Lord Chancellor and the establishment of the Supreme Court; it lent a little intellectual ballast to Speaker John Bercow’s all-too-successful manoeuvrings to “rebalance” the Commons from the government to the back benches; it even offered a top-dressing to the recent contentious ruling of the Supreme Court on the government’s power to prorogue parliament.

Each one of these steps was damaging; taken together they have led to the present parliamentary impasse and serious, and perhaps irreversible damage, to the fabric of the historic British constitution.

Which make the origin of Montesquieu’s doctrine all the more ironical, since it was England. Or rather the early 18th-century transformation in the status of England — or Great Britain, as she became known after Union with Scotland in 1707. Before the Glorious Revolution of 1688/89, England had shrunk to little more than a protectorate of Louis XIV’s France. But following the Glorious Revolution, and with astonishing speed, England first challenged and then defeated France in a series of great victories that culminated in the Battle of Blenheim in 1704.

Prior to this sequence of events, there was no reason why anyone should much concern themselves with the affairs of England. Afterwards, the question became insistent. For England and France now represented in theory — and to a considerable extent in practice — polar opposite models of government.

In France, where the Estates General or Parliament had last been summoned in 1614, King Louis XIV revelled in the untrammelled royal power exemplified in his motto of le roi gouverne par lui-même (“the king rules by himself”). But in England after 1689, the King, far from ruling alone, had to govern in cooperation with Parliament; and far from enjoying untrammelled power, he had to have the religion of the majority of his subjects.

Even King William III, the Anglo-Dutch prince brought in to wear the crown of this novel royal republic, sometimes fretted at the humiliation. But the paradox was that, far from weakening the power of the British state, the Revolution and its aftermath multiplied it several fold. And, still more puzzlingly, the powers of this strengthened state also proved compatible with increased individual liberty. Indeed, it could be argued that they depended upon it.

Montesquieu, who is also reckoned as one of the fathers of anthropology, decided to investigate this mystery by a two-year field-trip to England in 1729-30. Two years is a long time and quite enough for an intelligent man to inform himself seriously of the affairs of another country. But Montesquieu moved exclusively in a high aristocratic circle that was both francophile and French-speaking. And he never learned enough English properly to break out of it. The result is that his surviving notes consist of little more than society tittle-tattle.

Only in his Spicilège or scrapbook is there something more substantial. In the summer of 1730 a pamphlet war broke out which transfixed London. On one side was The Craftsman, the mouthpiece of Lord Bolingbroke, the brilliant but untrustworthy leader of the Country Party/Tory opposition; and, on the other, The London Journal, which defended the government of Sir Robert Walpole.

The Separation of Powers is not rooted in observation or analysis but in Montesquieu’s plagiarism of a shallow and partisan political pamphleteer

Walpole, the first and still the longest-serving prime minister, had just attained the summit of his power in May 1730. The key to his achievement was “his unique blending of the surviving powers of the Crown with the increasing influence of the Commons”. Bolingbroke, in contrast, believed the opposite. “England”, he proclaimed, “under the administration of Walpole, is degenerate and moribund, and the traditional vigour of the nation can be restored only if the House of Commons is freed from ministerial [that is, royal] control.”

“In a constitution like ours”, Bolingbroke repeatedly asserts in The Craftsman, “the safety of the whole depends on the balance of the parts, and the balance of the parts on their mutual independency on one another.” In other words, Bolingbroke believed in the Separation of Powers and Walpole did not. Instead he and all his successors practised the opposite. Or, as The London Journal put it:

’Tis plain to common sense and the experience of all the world, that this independency is a mere imagination; there never was really any such thing, nor can any business be carried on or government subsist by several powers absolutely distinct and absolutely independent.

The truth of which, it can be added, has been proved abundantly by the political disaster of the last two years of an “independent” parliament.

Which is where the Spicilège comes in. It shows that Montesquieu not only read the relevant issues of The Craftsman but copied crucial sections in his own hand and in his awkward franglais. And, following on from this, in The Spirit of the Laws he borrows Bolingbroke’s argument for the Separation of Powers uncritically, wholesale, and in defiance of the facts of the British constitution then and ever since.

Such, I am afraid, are the tawdry origins of the central doctrine of modern bien pensant political thought. The Separation of Powers is not rooted in observation. Nor in serious analysis. But in Montesquieu’s plagiarism of a shallow and partisan political pamphleteer.

Is it any wonder that the attempt to apply the doctrine has been so universally disastrous?