Attorney-client privilege is a fixture of any TV show that involves the law. But attorney-client privilege is also surprisingly complex. There are rules, exceptions to those rules, and exceptions to those exceptions. And yesterday, the United States Supreme Court heard oral arguments on one of those complexities. GBH legal analyst Daniel Medwed joined Morning Edition co-hosts Paris Alston and Jeremy Siegel to explain. This transcript has been lightly edited.

Paris Alston: So, Daniel, first of all, I've got to ask you: How many of the Supreme Court justices do you think watch "Breaking Bad," or have watched it in this case?

Daniel Medwed: Maybe one.

Alston: Attorney-client privilege is one of those things that we hear about all the time on shows like "Breaking Bad," "The Wire," "Law and Order." But it's really much more nuanced than just us everyday people watching TV might realize. So tell us about some of its basic principles.

Medwed: Let's break it down by dividing it into its theory, and then its practice.

So first, its theory: The rationale here is that we want to promote full and frank exchanges between a lawyer and her client. That's the only way for a lawyer to figure out whether or not there's a good defense. They need to know those embarrassing, incriminating details, and a client has to feel comfortable conveying them to the lawyer. Likewise, the only way for a client to figure out whether they have a decent option or what their likelihood of success is at trial is for the lawyer to give an informed decision. So it's a mutually beneficial, full and frank exchange of ideas.

Second, how do we convert that theory into action? The way we do it is we vest a privilege or an option in the hands of a client, which allows the client to prevent the court from getting access to certain information about the lawyer-client relationship. But get this, and this is the really important piece of it: Not everything is covered by the attorney-client privilege, only confidential communications that are made for the purposes of legal advice. So if it's not a communication, it's not confidential, [if] it's not for purposes of legal advice, it's not going to be covered. Those are sort of the basics.

Jeremy Siegel: So, Daniel, you're a lawyer, right? Let's say you're my lawyer, and I tell you I did something bad — maybe something incriminating — last week, like when Paris got up out of the studio, I took some of her cough drops.

Alston: Jeremy! My Halls Breezers?

Siegel: And sold them to our midday host, Henry Santoro. If that happened, and if I told you about that, those facts can't be disclosed in court, right?

Medwed: Well, it depends. It's a little more complicated. So let's say on the one hand, yes, Jeremy, your confidential disclosure to me, your lawyer, about your theft of your dear co-host's cough drops — poor, poor Paris, my heart goes out to you.

Alston: My throat is going to be so dry.

Medwed: You talk all morning and your co-host is stealing your throat drops.

That would be covered, Jeremy, because you are seeking legal advice from me, presumably about your criminal exposure, your legal liability, and so on. But on the other hand, I often like to say that the attorney-client privilege doesn't immunize the underlying facts in the communication from disclosure. It just immunizes the conversation. So, Jeremy, if you were to tell someone else, like if you were to tell associate producer Rachel Armany, 'Hey, I stole Paris' throat drops,' Rachel could be subpoenaed to testify because there isn't, believe it or not, a Morning Edition privilege. There should be, everything you say, and the team should be privileged, but it's not. So basically, those facts could come out — not through me, your lawyer, but through Rachel.

Alston: See, now I'm sitting here, I'm like, I would ride or die for my Morning Edition teammates, Daniel. But they're over here plotting behind my back.

Siegel: You can make money off of cough drops.

Medwed: Well, you can hold out, right? You could just be held in contempt of court and thrown in the hoosegow for a couple of days.

Alston: But oh, my goodness. OK, so what if in this case, Jeremy doesn't tell you about this this cough drop theft, but instead tells you about his intent to say, take my water bottle next? Is that privileged information?

Medwed: It actually isn't. And here's why. So if Jeremy tells me, his lawyer, about a past event to get legal advice about its exposure, that's covered, that's classic attorney-client privilege. But there is an exception called the crime fraud exception. If he's seeking legal advice about plotting a future or an ongoing fraud, we don't want to make lawyers complicit in all of this, and so that information could be disclosed. So I think Paris, your water bottle is safe, maybe not your cough drops.

Siegel: Tell us about this case in the Supreme Court. What aspect of the privilege does it concern?

Medwed: Sure. So the case that was heard yesterday — it's called In Re Grand Jury — is all about the scope of legal advice. And when you have a conversation with a lawyer that has a dual purpose, maybe part of the conversation is legal advice, but part of the conversation is business advice or tax accounting advice or lobbying advice, to what extent is the whole conversation privileged?

So here's what happened in that case. An anonymous client wanted to expatriate, which is harder than one might think if you have a lot of assets, because of your potential tax liabilities. So this person consulted with a nameless law firm to try to get advice. That person then became the subject of a criminal investigation, and the feds wanted to get access to information about the communications between the client and the lawyer, citing the fact that a lot of this advice was about tax accounting and business organization. The lawyer balked and basically said, "Hey, wait, part of our conversation was about the law. Therefore, all of it should be shielded."

Basically, it's a debate, and it might seem technical: If the primary purpose of the conversation is legal, it should be shielded. But what if just a significant portion of it — not the principal or primary portion, but just a significant portion — is legal? Does that protect everything or not? And it's important for the following reasons: If you only have to talk a little bit about the law with your attorney to make the whole conversation privileged, you could see scenarios where at a big company, all of the business people are coming up with a scheme or a plan, and they simply copy the lawyers on the email as a way to keep it privileged. So the stakes are not huge here, but they are relatively important.