When was the last time you used some variation of the phrase “Thank you”? At the coffee shop this morning? While you were having dinner last night? Because someone held the elevator for you?
How about online? Have you used it to sign an email recently? Did you intentionally not use that phrase? And did you stop to think about what that really meant?
The phrase “Thank you” is part of a triad of ritualized responses we learn in early childhood that also includes “Hi” and “Goodbye.” The latter two represent transitional linguistic points that signal increased and decreased access to certain states of interaction. “Hi” both acknowledges a relationship and opens the interaction, while “Goodbye” marks the conclusion of the interaction. In the United States, it is an expression of appreciation. “Thank you” plays a mediating role in sustaining relationships where social access is possible.
For the rest of the story: http://blogs.scientificamerican.com/anthropology-in-practice/2013/06/11/why-are-we-signing-our-emails-with-thank-you/