One of the most interesting questions in the world of modern entertainment may soon be pondered at Europe's top court: can people resell the e-books that they buy?

This question is vital in the digital era, and relevant not just to the world of book publishing, but also the realms of music, film, and games. You're able to resell the CDs and DVDs that you buy, so why can't you do the same with downloaded copies of albums and movies?

The case involves a Dutch second-hand e-book platform called Tom Kabinet, which took a previous ruling by the European Court of Justice, involving second-hand software, as the go-ahead for its own business model. Since 2014, Tom Kabinet has been at war with the Dutch Publishers Association (NUV), which sees it as a threat to the entire book industry.

The next step in this long-running saga is the decision of the Dutch supreme court in The Hague, which is currently scheduled for June 1, its original due date of April having been postponed at the last minute. Many expect the Dutch court to refer the case to the European Court of Justice (ECJ), to clear the question up on a pan-EU basis.

Update, June 2: The ruling has been delayed yet again. We don't yet have a new date for the ruling.

How do you ensure the e-books aren't pirated?

Here's the story so far. In 2014, the publishers tried to get Tom Kabinet shut down, but the Amsterdam district court refused to grant them a cease-and-desist order. In an early-2015 preliminary ruling, the Amsterdam court of appeal backed this earlier ruling, but said Tom Kabinet had to ensure that its platform wasn't being used to sell pirated e-books.

The company cleared its virtual bookshelves and started over with a new twist on its model, requiring sellers to provide the original download links and prove they had legally bought their e-books. The platform only deals in open formats, as the digital rights management used by the likes Kindle and iBooks make resale impossible.

Tom Kabinet also tried to get into the business of reselling new e-books, only to find the three big Dutch publishers were blocking the country's central book distributor from supplying it—which prompted a swift complaint to the Dutch competition authority.

While it waits for that investigation to go somewhere (the regulator won't comment), Tom Kabinet has since become a sort of book club. To use it, you offer up the download link for your purchased EPUB e-book and, in return, you get credits. Buying a book from the collection costs €2 plus a certain number of credits (depending on how new the book is) and, once you're finished with the book, you can return it to the pot in exchange for credits—as much as 80 percent of what you paid, if you resell it within four weeks.

But the main question still remains unresolved: is it legal for consumers to resell e-books at all? German courts have suggested the practice should be stopped, while Dutch courts think it's kosher. But as they're dealing with the same EU law, they can't both be right.

To find out why this is such a confusing issue, we have to go back to the 2012 ECJ judgement that birthed Tom Kabinet in the first place—the Oracle v UsedSoft ruling.

Like most digital law, it all started with Oracle

UsedSoft, a German company that sells second-hand software, was buying and reselling Oracle software licenses from Oracle's customers, either whole or in part—these were group licenses for 25 users, so customers were sometimes left with "spare" seats they didn't need. The German firm was then reselling these licenses to its customers, who could use them to download Oracle's products.

Oracle pointed out that its license terms said use of the programs was non-transferable. It sued UsedSoft and won twice in Germany, before the reseller appealed to the ECJ.

The crux of the ECJ's ruling was this: once the copyright holder of the software (Oracle in this case) has sold the product, it doesn't get to stop the buyer from selling it on as she wishes. Its rights as the seller are "exhausted" in that first sale. In Europe, this is known as the "principle of exhaustion"; in the US, it's called the "first-sale doctrine."

That decision became a landmark interpretation of the EU's 2009 Software Directive. The directive clearly said the principle of exhaustion applied to a purchased copy of software. However, before the ECJ's ruling, there was some debate over whether this applied to "intangible" downloaded software as well as more traditionally packaged products.

As is the norm these days, Oracle claimed it sold not the software but the license to use it. The court was unimpressed by this argument, noting that there is no point downloading something if you can’t use it, and calling the software-license bundle "an indivisible whole." It said the principle of exhaustion was not limited to copies of software sold on physical media, and vindicated UsedSoft's business model—up to a point.

Most importantly, the court said the Oracle customers selling to UsedSoft could only do so if they made their own copies unusable. This meant people couldn't sell off unused slots in their Oracle bundle and keep using the ones they needed.

Oracle claimed it might be impossible to know whether the reseller had rendered the original copy unusable. True, said the ECJ, but the same applies to software sold on physical media such as DVDs—that's what protective measures such as product keys are for.

In short, if you've legally bought genuine software, or the license to use that software forever, you get to sell it on no matter what format you bought it in, and no matter what the licensing terms say. That's the EU-wide legal precedent.

The precedent for what, though? The UsedSoft ruling was based on the EU's 2009 Software Directive, but things like e-books and music albums fall under a separate piece of EU legislation, the 2001 "InfoSoc" Directive on copyright and related rights in the information society.

It so happens that the InfoSoc Directive contains almost exactly the same wording as the Software Directive when it comes to the exhaustion of rights, but the UsedSoft ruling—the only ECJ judgement on intangible downloaded goods and the exhaustion of rights—specifically relates to computer programs, not all digital goods.

So that's why the courts are still confused. However, should the resale of digital goods be legal?