Trading stocks, targeting ads, steering political campaigns, arranging dates, besting people on “Jeopardy” and even choosing bra sizes: computer algorithms are doing all this work and more.

But increasingly, behind the curtain there is a decidedly retro helper — a human being.

Although algorithms are growing ever more powerful, fast and precise, the computers themselves are literal-minded, and context and nuance often elude them. Capable as these machines are, they are not always up to deciphering the ambiguity of human language and the mystery of reasoning. Yet these days they are being asked to be more humanlike in what they figure out.

“For all their brilliance, computers can be thick as a brick,” said Tom M. Mitchell, a computer scientist at Carnegie Mellon University.

And so, while programming experts still write the step-by-step instructions of computer code, additional people are needed to make more subtle contributions as the work the computers do has become more involved. People evaluate, edit or correct an algorithm’s work. Or they assemble online databases of knowledge and check and verify them — creating, essentially, a crib sheet the computer can call on for a quick answer. Humans can interpret and tweak information in ways that are understandable to both computers and other humans.