meaning - "Nothing to tell" versus "nothing to say"

There's nothing to tell.
There's nothing to say.

Can anyone explain the difference between those two statements and give some examples on how they should be used? I think I do have a basic understanding, but I'd like to hear it from someone who knows this to the deepest roots.

Answer

"There's nothing to tell" is a response to someone's asking for details about an event or a story, where the responder implies that the information the asker wants to know doesn't actually apply to the event or story. For example:

Q: "What happened at the party last night?"

R: "There's nothing to tell."

(Nothing happened or things that you don't really care about happened, but that's it - i.e. I hung out for five minutes and went home.)

The responder could also say, "There's nothing to tell," in order to downplay what actually happened. For example:

Q: "It must've been really hard to become such a good swimmer. How did you do it?"

R: "There's nothing to tell."

(The answer is too long and/or boring, so I'll spare you the details.)

Another instance is your own suggestion of using "There's nothing to tell" to mean, "I don't want to tell you what happened."

"There's nothing to say" is very similar to "There's nothing to tell" in that the responder thinks any response the asker might expect either doesn't apply or doesn't matter. It's also possible that the responder doesn't really want to answer the question. The biggest difference is that "tell" generally involves some sort of story or narrative, and "say" involves some sort of issue or non-narrative topic. For example:

"I would love to visit Area 51. Wouldn't you?"

"There's nothing to say."

(I don't think it exists, so my response doesn't apply.)

"Do you think signing that bill into law was the right decision?"

"There's nothing to say."

(It doesn't matter what I think.)