Last year, Season 2 of the popular British TV series "Downton Abbey" yielded a bumper crop of linguistic anachronisms. In Season 3, now airing stateside on PBS, the out-of-place language has continued. There was a particularly glaring anachronism in the most recently aired episode: "steep learning curve."

My investigation into "Downton Abbey" anachronisms last season garnered a fair amount of attention, and inspired additional research into linguistic accuracy on the series. Benjamin Schmidt, a history graduate student at Princeton and fellow at Harvard's Cultural Observatory, has been approaching the matter more systematically on his Prochronisms blog, by using the Google Books Ngrams corpus to determine which combinations of words are the most unlikely to have occurred in the time period of "Downton Abbey" (currently set in 1920). His automated approach turns up anachronisms that most of us wouldn't have discerned just by watching, such as "Indian subcontinent." (Who knew?)

But it didn't require any fancy algorithms to pick up on a truly anachronistic bit of dialogue in the latest episode on PBS. Matthew Crawley, the presumptive heir of Downton Abbey and now the co-owner of the estate, says, "I've been on a steep learning curve since arriving at Downton." By this he means that he's had a difficult time learning the ways of Downton. Unfortunately, people didn't start talking that way until the 1970s.

If the screenwriter Julian Fellowes (or one of his researchers) had checked out the phrase learning curve to determine if it was appropriate for 1920, he might have seen from the Oxford English Dictionary that it dates from 1922 and figured this was close enough. Learning curve was indeed in use at the time, but only among scholars of psychology who were actually plotting such curves to study learning processes among humans and animals.

The concept of the learning curve was introduced in 1885 by the German psychologist Hermann Ebbinghaus in his book Über das Gedächtnis (About Memory). Ebbinghaus charted the rate of learning a task, in which there is a sharp increase after the first attempt, followed by a gradual plateau on subsequent repetitions as less information is retained. His book evidently wasn't translated into English until 1913, though the translation didn't contain the phrase learning curve.

In the meantime, though, learning curve began showing up in psychological journals. The earliest example I've found is in a 1903 article in the American Journal of Psychology by Edgar James Swift, entitled "Studies in the Psychology and Physiology of Learning." Referring to an earlier study, Swift wrote, "Bryan and Harter (6) found in their study of the acquisition of the telegraphic language a learning curve which had the rapid rise at the beginning followed by a period of retardation, and was thus convex to the vertical axis." In 1907, the phrase appeared in two studies of animal learning, one on raccoons and one on ants.

For a few more decades, learning curve remained in the field of psychology. It eventually came to be used in business management to describe how quickly a company masters new tasks and lowers costs, as when a newly introduced product needs to be manufactured. Boeing is said to have used the learning curve concept in the 1930s. But it didn't become a common phrase until the 1970s, and it was then that the word steep began to be used to modify it in a rather peculiar way.

If you consider a learning curve in which some measure of skill is on the y-axis and the number of attempts at learning over time is on the x-axis, then what would a steep slope represent? A rapid ascent to a higher level of learning. And yet the way that steep learning curve came to be used in the '70s suggests just the opposite: an arduous climb rather than a quick and easy one. The meaning thus became reversed from the earlier technical one.

Looking through examples of the expression from the '70s, one can find both positive and negative senses. For instance, an article in the Spring 1973 issue of Sloan Management Review about the computer industry includes this line: "Due to economies of scale and a very steep learning curve, the cost of such circuits has dropped by a factor of ten in a little over one year." An article in the February 11, 1979 edition of the Boston Globe about Texas Instruments says that "part of TI's success in having a steeper learning curve — and lower product costs when produced in mass — has been its 'design to cost' system." In both examples, a steep learning curve is a good thing, from the perspective of a business ramping up productivity and trying to keep costs low.

But the phrase was also being used by individuals describing a learning process more subjectively, and in those cases the sense became more negative, with steepness equated with difficulty. Thus, for instance, in December 1978, the newly appointed chairman of NBC, Jane Cahill Pfeiffer, told the New York Times, "I'm on a very steep learning curve, and the bulk of Fred [Silverman]'s experience is not where mine is." The following month, in January 1979, Lord Kearton, chairman of the British National Oil Corporation, had this to say to The Guardian: "Everybody in the North Sea is on a very steep learning curve. What worries us is the prospect of new people coming in with practically no resources of any scale, who will have to start more or less at the bottom of this curve."

It was uses like these (notably both from titans of industry) that helped popularize the notion that a steep learning curve was an arduous and not an easy process. Because that semantic shift didn't happen until more than a half century after the time that Matthew Crawley is supposed to have used the phrase, I hereby anoint steep learning curve as the most egregious blooper ever to have been uttered by the good people of Downton Abbey.