Where does hmm come from?
While English speakers have likely long been making hmm sounds in everyday speech, hmm isn't attested in the written record until the 1850s, probably as a variant form of hum, hem, and h'm, evidenced by the late 16th century. A simple vocalization, hmm is also incredibly versatile, used with different tones to mark discourse in many ways.
Hmm can request clarification with rising intonation: “Hmm? I didn’t hear you—say what?” It can reinforce a concern when inserted midway or at the end of a question: “What’s wrong, honey? Hmm? What’s going on?” Hmm can indicate thought or reflection with a steady tone: “Hmm, I’ll need to look into that.” An elongated hmmm can express thinking more deeply. The interjection can express wonder or surprise when uttered briefly and at a higher pitch: “Hm! I never knew that!” It can show curiosity or uncertainty: “Hmm, wonder what’s for dinner.” Hmm can convey irony or suspicion: “Baked a dozen cookies this morning. Two left. Wife says she doesn’t know but chocolate’s all over her mouth. Hmm.” Hmm can also signal dissatisfaction or disagreement, often as a curt, low-pitched hm: “Hm. Yeah right. Like you really mean it." Sometimes, hmm just acts as a place-holder or fills a pause in a conversation: "It's been great talking with you. Well, hmm, guess I should be going, though."
As the many meanings of hmm spread into writing, hmm also took on a life of its own online. Social-media feeds, such as Reddit’s /r/hmm message board or Twitter’s "#hmm" hashtag, designate content that "makes one go hmm," or consider something with wry skepticism. This hmm is used to comment on the oddity or ridiculousness of some image or situation.
Who uses hmm?
As noted, hmm is prolifically used in everyday conversation and colloquial writing. Its meaning widely varies based on context and intonation.
In digital communication, use of hmm to indicate thought or irony are particularly widespread. To help indicate such tone, many users supplement or substitute hmm with the Thinking Face emoji 🤔. The Neutral Face emoji, 😐, is sometimes paired with hm, expressing a gruffer dissatisfaction.
Hmm is not to be confused with mmm, communicating pleasure, or mhmm, which shows acknowledgment or agreement.
Hmm I think I may change the battery
@ashens, April, 2018
Thought you were safe, hmm? #Splatoon2 #NintendoSwitch
@TropicasHeroes, April, 2018
Sugar? Check. Tobacco? Check. Trans-fats? Check. Hmm, what other substantive vice does New York Mayor Michael Bloomberg have left to crack down on? Oh, alcohol!
Dino Grandoni, The Atlantic, January, 2012