One of the hottest start-ups this year was Persado and their “marketing language engineering.” Co-founder Guy Krief led a energetic session at SXSW called, “The Power of WordPlay: Science Meets Language” — but another name for it could be “Computers Always Write The Best Messages.”

While the session may have been dispiriting for copywriters in the audience, it offered insights for anyone tasked with creating marketing messages that break through the clutter.

The reason Persado’s marketing language engine can create the “best” messages (and lift conversion rates anywhere from 30 to 100 percent), according to Krief, is its ability to analyze all components of a message—usually a product, offer, and emotion—and run millions of variations in just minutes. And then test them.

No human can work that fast (or would want to). The ability to test and send millions of messages quickly reveals useful patterns.

Here are a few learnings on subject lines:

• Negative emotions (words such as “hurry up,” “don’t miss out,” anything anxiety inducing) generate CLICKS but have a bad impact on conversion (in Latin America, however, this tactic does work)

• Optimism is the best emotion to use for conversion

• Descriptive subject lines are the most successful

• Highly emotional words are often marked as spam and can cause expectations to be too high

• There is no ideal subject line length as long as it does everything else right (i.e. short subject lines are NOT always better)

• Avoid conjugating verbs in subject lines

• If a client claims “you can’t say that” or “this won’t work”, it’s most often an outdated assumption; many so-called “best practices” have never been tested

Take a look at Persado’s site to see how it works and explore the technology.

There are many places this technology can go—soon the engine may be able to automatically customize a message based on target audience, for example. For now, human writers will simply need to do our best to keep up.