Isaac Newton argued powerfully that it was. His views evolved over time, but from early on he understood that money was a unit of exchange and not, necessarily, a physical thing. In a letter to one of England's currency conservatives, Newton displayed a strikingly contemporary outlook. "Credit," he wrote, "is a present remedy against poverty & like the best remedies in Physick works strongly & has a poisonous quality." Hence, Newton argued, caution was indicated--but not total rejection of what could be a useful tool. "Good physitians reject not strong remedies because they may kill," he wrote, "but study how to apply them with safety & success." And, Newton emphasized, credit was useful: "If interest be not yet low enough for the advantage of trade and designs of setting the poor on work ... the only proper way to lower it is more paper credit till by trading and business we can get more money." Even more radically, he wrote, "'Tis mere opinion that sets a value upon [metal] money; we value it because with it we can purchase all sorts of commodities and the same opinion sets a like value upon paper security."

Mere opinion? That was much further than most of his contemporaries were prepared to go. No matter--Newton, above all people, understood that paper money, exchangeable promises, bonds, and the like are all abstractions. To understand them, to accept them, took a capacity for the kind of mathematical reasoning that was just beginning to infiltrate all kinds of fields, including Newton's new physics. The scale of the risks associated with manipulating disembodied expressions of value was perhaps less clear to Newton than it may be now--though he would learn, to his sorrow, of the potential for catastrophe when he lost a substantial fortune in the South Sea Bubble of 1720. Even so, he grasped the idea at the heart of financial reasoning: that transforming distinct chunks of material reality (such as physical coins) into abstractions that can be manipulated numerically makes it possible to analyze the behavior of a system on a much deeper level--whether one is thinking of motion, of gravity, or of money.

What does all this have to do with Newton's correspondent? William ­Chaloner was hardly a scientific revolutionary. But he had wit enough to seize the opportunities created by revolutionary changes in thought and practice. He recognized that there was much more to be made in printing 10-pound notes than in casting pot-metal shillings or half crowns one by one. So in the summer of 1698, he acquired a malt lottery ticket and used it to guide him as he engraved a plate that enabled him to print hundreds of copies. The first of his fakes was found in circulation that October--and the Treasury panicked at the thought of the blizzard of false paper that might follow.

It fell to Newton to stop him: the Warden of the Mint had the duty to pursue currency crime. Several hundred surviving documents detail that investigation. Among them are records of dozens of interrogations, payments to undercover informers, even accounts of Newton's own expenses in dodgy pubs as he questioned witnesses around London.

Newton formed the pile of paper in his files into an unbreakable chain of evidence. The court took less than an hour to convict Chaloner, minutes to sentence him to death. That was when he wrote his last, piteous plea to Newton.

It didn't work.

Around midday on March 22, 1699, Chaloner climbed the ladder to the top of the scaffold and bent to the noose. Isaac Newton, at work at the heart of England's money supply, did not choose to watch the show.

Thomas Levenson, author of Newton and the Counterfeiter: The Unknown Detective Career of the World's Greatest Scientist, directs MIT's Graduate Program in Science Writing.