Soon after Apple's iPhone went on sale six years ago this week, you probably started spotting hastily-written emails appended by the words "Sent from my iPhone." And then, a bit later, you spotted a lot more. Of course, the iPhone was not the first email-enabled smartphone to attach such a message to outgoing emails. So did various Treo handsets (remember those?) and BlackBerry phones, pre- and post-iPhone. The iPhone's instant success, and its default signature, simply made the practice far more prevalent. Alongside this trend, a different but related one emerged: the iPhone's stock signature, at first deemed a louche emblem of status, became a built-in forgiveness clause. Please don't judge me for any typos or spelling errors, "Sent from my iPhone" suggested. I am very busy. That's according to a chart published on Tuesday by the author Clive Thompson, who drew data from a 2012 Stanford study on the perceived credibility of misspelled emails sent with (and without) a "Sent from my iPhone" signature:

Thompson comments on the findings of the study, which asked a group of Stanford students to assess the credibility of emails, some of which had the signature, others of which did not:

When the message had correct spelling, grammar and punctuation, the sender was rated as being very credible — and there was little difference between whether the email seemed to have been composed on a computer or a phone. But when the message had errors in it, things changed: Students attributed higher credibility to the person who’d written the lousy message on a phone.

For these results, Thompson credits "linguistic code-switching" — whereby people speak differently among friends, family, and coworkers — and theorizes that the prevalence of AutoCorrect software has, paradoxically, made misplaced words and punctuation more acceptable in digital communication. (But no less funny.)

Indeed, the sociological implications of email signatures go fairly deep, according to others who have studied the subject. In 2006, for example, the technologist Michael Silberman argued that the signature suggested a particular affection for the email's recipient. "If we're responding to you from our phone or BlackBerry, it generally means that we're going out of our way to respond under some inconvenient circumstances," he wrote. "It's not like we took our phone to the cafe to catch up on email. We're risking our life to respond to you while walking, eating, drinking, traveling, or juggling. You can thank us later."

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