Um, yeah, no, hmm...
Discourse markers are the little words at the beginning and ends of sentences that help people organize conversation and relate to listeners.
“I noticed ‘yeah, no,’ ‘no, yeah’ and ‘no, I know,’ where no seems to mean yes,” said Anne Curzan, an English Professor at the University of Michigan.
‘Yeah, no’ does a few things. It helps people agree with another person who has made a negative statement.
“So someone says, ‘I don’t think that rule applies here.’ And you can say, ‘yeah, no I don’t think it does.’ So you’re affirming a negative statement," she said.
Curzan tells Rina Miller, these "discourse markers" also help people politely disagree with someone.
“Let’s imagine someone says, 'Oh good there’s no group work,' and you say, 'Yeah, no there is group work.' So you’re acknowledging they’ve said it, but you’re respectfully disagreeing.”
And then, as Curzan says, people use it to do a “funny disprefered response.” Basically it's when people about to say "no" to someone.
“Let’s imagine someone asks me, ‘Anne, will you do this hundred question survey?’ And I say, “yeah, no.’”
‘Um’ is another way to signal to another person that you are about to disagree, or say no.