Hmm vs. Umm — What's the Difference?

Difference Between Hmm and Umm

Used to express reflection, uncertainty, or hesitation

Hmm, interesting idea

Hmm, well I should probably get going

A coincidence? Hmm

Used to express doubt or uncertainty or to fill a pause when hesitating in speaking.

Indicating thinking or pondering.

Hmm... that's an interesting idea.

Hmm... I just can't decide between the two.

Hmm... creation or evolution? That’s the big question.

Implying hesitation.

- How does a plane fly?

- Umm, I don't know.

A demand for an answer to a question.

Just where were you until 2 a.m.? Hmm?

To make the umm sound to express confusion or hesitancy.

(intransitive) To make a thoughtful humming noise.