I don't know

1. I'm unsure about something; I don't have a response or suggestion right now. Often used in an evasive manner when one cannot, or does not want to, answer a particular question. In informal speech, the words are commonly contracted together as "I dunno." I don't know how we can help them, I really don't. A: "Why on earth did you throw a baseball through their window?" B: "I dunno, Mom—I'll pay them for it, just leave me alone." A: "Hey, answer me. Why do you smell like cigarette smoke?" B: "Mom, geez, I don't know. Somebody down at the park must have been smoking." A: "That 'someone' better not have been you!"

2. Used rhetorically to emphasize that one is merely speculating or offering something as an impromptu suggestion. Sometimes used sarcastically to indicate that the suggestion should be obvious to the other person. A: "We need to increase sales. Does anyone have any ideas?" B: "Well, how about, I don't know, offering a 10%-off coupon to everyone who spends over $50?" A: "I can see someone breaking into the house across the road! What should we do?" B: "How about you, oh I don't know, call the police? Sheesh!" If you're still feeling sick, why don't you, I don't know, call the doctor?

I don't know.

a common expression of ignorance or of lacking an answer. Father: Why can't you do better in school? Bill: I don't know. Bill: Well, what are we going to do now? Sue: I don't know.