Know your audience. It separates us from the apes.

[W]hat animal psychologists call theory of mind is the ability to infer what another animal does or does not know. Baboons seem to have a very feeble theory of mind. When they cross from one island to another, ever fearful of crocodiles, the adults will often go first, leaving the juveniles fretting at the water’s edge. However much the young baboons call, their mothers never come back to help, as if unable to divine their children’s predicament.But people have a very strong ability to recognize the mental states of others, and this could have prompted a desire to communicate that drove the evolution of language. ‘If I know you don’t know something, I am highly motivated to communicate it,’ Dr. [Robert] Seyfarth said.

How can we use this tantalizing observation (reported in the New York Times) to communicate more successfully? In particular, how can we know if someone doesn’t know something? Partly, it depends on age.

Grownups: Consult Hitting the Sweet Spot: How Consumer Insights Can Inspire Better Marketing and Advertising by Lisa Fortini-Campbell. First published in 1992, it remains a classic, as we said in an earlier issue of The Editorial Advantage.

Older teenagers: Send them a text message or instant message and wait 30 seconds. According to research quoted in Forbes, 71% of kids age 13 to 17 use instant messaging, and more than half of this age group uses text messaging. Of course, getting a straight answer out of them is another matter.

8 to 14: Download a wireless device called Radar from eAgency Inc. to monitor incoming and outgoing calls, e-mails, text messages, and video. A message alerts the child that he or she is being monitored. Walter Mossberg’s Website reviews it favorably.