Songfacts®:

• This song, in which Mayer confesses to being half-hearted in a relationship, is a collaboration with Country-Pop star Taylor Swift.
• Mayer told MTV News that the idea for the song came to Mayer in a dream. "I woke up with the song in my head called 'Half of My Heart,'" he recalled. "And the idea is that it's this real sort of updated - not that it needs to be updated - sort of Tom Petty, Fleetwood Mac, Stevie Nicks thing."
  He added. "I thought, 'Well, if this is going to be my love letter to that style of music, who's going to be the Stevie Nicks in this equation?' And I thought, 'This Taylor Swift girl is going to be around for a long time.'"
• John "tweeted" about wanting to record the song with Taylor back in March 2009: "Waking up to this song idea that won't leave my head. 3 days straight now. That means it's good enough to finish," he wrote on his Twitter page. "It's called 'Half of My Heart' and I want to sing it with Taylor Swift. She would make a killer [Stevie] 'Nicks' in contrast to my 'Tom [Petty]" of a song."
• It has been said that Mayer's former beau, Jennifer Aniston, got annoyed with the singer spending more time on his Twitter updates than with her. His explanation of the lyrical content of this song to The London Times January 2, 2010 suggests that the rumor is true. He explained that it's about "questions of, do I want to share my desires with someone else or do I just want to sate them myself with my laptop and my Twitter account? - these are substituting relationships. Knowing that I could blog right now from my iPhone and it's up on the internet with people reading it and responding to it. How much is that a synthetic version of having dinner with somebody? How intimidating must it be to try to find an 'in' with the man who is consistently satisfying himself by all means necessary? Where is her place in that?"