Most new patents are combinations of existing ideas and pretty much always have been, even as the stream of fundamentally new core technologies has slowed, according to a new paper in the Journal of the Roayl Society Interface by Santa Fe Institute researchers Hyejin Youn, Luis Bettencourt, Jose Lobo, and Deborah Strumsky.

Youn and colleagues reached those conclusions sifting through the records of the United States Patent and Trademark Office. Dating back to 1790, the records feature an elaborate system of technology codes - a vocabulary of sorts, in which any new invention is a phrase.

The researchers found that throughout the USPTO's history, about 40 percent of patents have been refinements on existing patents that leave the "phrase" unchanged. The rest are either new words or new phrases - and the balance between those has changed.

"Suppose you write a long novel. You may emphasize the introduction of new vocabularies or the introduction of new phrases," says Youn.

The vocabulary of invention grew exponentially until 1870. Afterwards the expansion slowed, but by that time there were so many basic technologies that inventors could keep up the pace of new patents only by combining old "words" in new ways.

Youn says there are a number of avenues for future research. In one project, she and colleagues are examining the grammar of technology - the different ways that individual ideas are combined or not--and how that grammar's changed over time.