"My brain," as one reader put it rather dramatically, "fell over at the thought of selling 'used' ebooks". He wasn't the only one. The reaction to the news earlier this year that Amazon had a patent to sell secondhand ebooks was almost universally strong: it could ruin authors' livelihoods, said some commenters. It was dangerous for publishers, said others. It's just boggling my mind, said most.

These are the details we have: the patent is for an "electronic marketplace for used digital objects", where "when the user no longer desires to retain the right to access the now-used digital content, the user may move the used digital content to another user's personalised data store when permissible and the used digital content is deleted from the originating user's personalised data store". Amazon has not commented publicly about it, and it's possible that the book retailer may not be planning to do anything at all with the patent – that it was a defensive move.

But add it to the news last year that a Kindle user had her entire library wiped by Amazon without warning and the fact that, a few years ago, readers woke up to find that their digital copies of various books by George Orwell had vanished from their Kindles, and the possibility that ebooks could be sold as secondhand goods becomes another reminder of the sheer slipperiness – the intangibility – of the mushrooming digital product.

It used to be that a book was published, and that was it. Permanent, physical, tangible, it could be referred to for as long as the copy survived. That's not the case any more. We live in a world where page numbers – if they exist at all – don't correlate from device to device, where digital text can be updated at the touch of a button, where the ebooks we own can vanish without our say-so. It's something which is becoming a real issue, particularly for academics.

"I think it is a very grave problem," says Robert Darnton, scholar, author and Harvard University librarian. "If you're citing a digital version of a book, often you can't cite the pages." He adds that that documents have always been slippery – "there's no definitive text of King Lear" – but the ease with which it is now possible to make changes to published ebooks means "you take a problem like that, multiply it by 1,000, and that is the world we are in."

The issue is compounded, he says, "by the fact a lot of digital texts suffer from faulty editing, not to mention the hands of the scanners [appearing on pages]". He promises that the Digital Public Library of America, which launched last week, will "redo a lot of digitisation and make it right", as well as build in the capacity to make precise references.

"It is a mess, this world of digital texts," says Darnton. "We are living in a very fluid moment. Everything's changing. Nothing seems stable."

Angus Phillips, director of the Oxford International Centre for Publishing Studies at Oxford Brookes, agrees. "They are starting to put page numbers in some ebooks, and you can do percentages, but it is a bit irritating when you want to reference the pages," he says. "When you're reading and you want to look back, yes, ebooks have got a great search function, but with a physical book, I can flick back. Put [a term] into a search function, you might get 30 different references."

He also worries about what the possibility to update ebooks will mean for quality. "For authors, the printed book means you've finished and that's the final format – you can't keep revisiting it," he says. "You want the author to know this is the final version. If authors have 10 bites of the cherry, will they concentrate as hard as if they think it's the final version? There's a feeling with the web that you can put something up there, and people can change it. One of the advantages of books is that they're permanent."

The ability to update ebooks is there, however. "Publishers can make changes to their books and send us updated files any time," says an Amazon spokesperson.

But "we don't want to be in a situation where someone's book changes without them knowing – that would be bad practice," adds Michael Tamblyn, Kobo's chief content officer. "We do have it in our ability to provide alternative editions of material but it doesn't happen that often – it's a fairly rare thing. Most publishers are very conscious of the integrity of a published book – certainly as a consumer you wouldn't want your book to get shorter, for example."

Amazon says that at present, "if a new version of a book becomes available, the customer is notified and gets to choose if they would like an update, and they can do this in an automated way. They also get to keep their place in the book as well as their notes and highlights."

Textual slipperiness aside, there's also the gnarly issue of who, exactly, owns an ebook. John Scalzi, bestselling novelist and president of the Science Fiction and Fantasy Writers of America, is up in arms over Amazon's secondhand ebooks patent (it was on his blog where the reader's mind fell over).

"We don't know exactly what Amazon's planning to do with this. Every tech company out there files patents for things, but they don't necessarily have a plan to use them," he says. "On the other hand … there is likely to be interest in a secondhand market for electronic books, and the question then becomes how we balance the consumers' rights with the simple fact that pristine electronic copies of books are likely to undercut the incomes of the creators."

Scalzi can understand why consumers might be interested in selling on their ebooks – but "is an electronic file exactly the same as a physical object?" he ponders. "Some say absolutely, no matter what, if you buy it, you've bought it. Others say, if I have a book and take it to a used book store, when I give them the book, it's gone, whereas with an electronic book, it's possible I can make a copy for my archive, and resell the pristine-looking copy."

The issue, it seems, boils down to two things – does a reader own an ebook, or the licence to read an ebook? (Amazon's Kindle terms state that "Kindle content is licensed, not sold, to you by the content provider".) And is it possible to trust readers who wish to sell on their used ebooks not to have secretly made a copy, or two copies, or hundreds of copies, which they're handing out to all and sundry?

"If a large company like Amazon begins selling used works, are people who conscientiously go out of their way to buy books rather than pirate going to see a difference between a new file and an old one, one of which goes to pay me, and the other doesn't?" wonders Scalzi. "It's a very real concern for writers and other creators."

But he isn't panicking quite yet, because he believes that if Amazon, or another online book retailer, begins to sell used ebooks, there's likely to be a whole lot of legal action. "The legal ramifications are fascinating. If Amazon or whoever start selling these electronic files, and it could be proved that someone had made a copy, then we're looking at a really interesting class action suit. It could take years to go through court, and the legal right to sell could get halted while it went through the courts. That would do two things – give writers and publishers some time to figure out the ramifications, and have an effect on consumer behaviour. Regardless of what happens, nothing about this is going to come easy or simply or without a huge amount of legal litigation and ramifications," says Scalzi.

The novelist doesn't think the changes are all bad. "It is part of the overall conversation of what happens when an industry shifts. And in every shift in technology there will be some positives and some negatives."

Darnton, too – despite all his worries – is feeling positive. "As things change new possibilities open up, but we need to reach a point where we can stabilise at least the textual element. That's part of the mission of the Digital Public Library of America."