how do you know when to stop reading?

When a voice in my head says, "this is not very good and its not getting any better."

I will put up with a book that has detectable merits far longer than one I see no hope for. If it is just a matter of my mood clashing with the book, I will stop reading it, but I won't 'give up' on it and will often try again at a later time.

I have been known to abandon a book after half a page. That is pretty common, really. Alternatively, I've been known to abandon a book when I'm halfway through it, but that is rare. There isn't a hard and fast rule.

i'm trying to think of an example where i kept going even though i didn't like the book and then i really ended up liking the book. it has to have happened. too bad my memory is so poor.

i try to give most any book at least 10% worth of it to get going. i know i remember not liking Cryptonomicon through a good couple hundred pages but kept going and ended up liking it a lot.

I used to be incapable of giving up. Now I give them 50 or 100 pages (unless it's really shit) to win we over.

I give up really easy, but often wrongly. When the writing is genuinely bad or the plot is clearly contrived or cliched or something like that, I think it's quite justified to put a book down. Or with non-fiction when you realize you're in way over your head, like with some very academic histories. Otherwise I think it's good to plough ahead and see where a book is going.

I rarely ever put a book down unfinished and I usually feel really guilty about it, but I've done it at least twice this week. It's not because the books are bad, though, it's just that I don't know what I feel like reading right now. Valis is just kind of "blah blah poor depressed ex-hippies, I get it", and I can't work up much excitement about the other books I have lying around. I need a new author or something.

i just dont pick the book up again - then eventually i realize im not reading it anymore and it gets moved from the pile by the bed to the bookshelf

yeah it's all about piles for me too. if i'm reading non-fiction (which is kinda rare) and I REALLY disagree with something it will turn me off big time. i did that this week with Newton Arvin's Melville bio. but if i don't click with a book within the first 25-50-100 pages, it's time a new book.

My mother (the librarian) used to pick out books for me without my consultation, and if I didn't like the look of them, insist I wasn't allowed to give up until I'd read three chapters. If, after three chapters, I still wasn't interested, I was allowed to return the book.

This is still my rule of thumb. Although I didn't get past page 2 of The Da Vinci Code.

if instead of reading i am looking for something, anything, to watch on tv or idly playing on the internet, then it means i am not interested in the book and i should just read something else instead

i tend to read by accretion, just flipping to random pages and starting, then stopping. sometimes i read all the pages in a particular book, sometimes not.

Almost always, I'll plough on. I think the last book I gave up on was Moby Dick, about ten years ago.

I read the entire chapter on different kind of whales and still gave up on Moby Dick. Maybe if I hadn't known how it ends.

When I find myself skimming entire chapters just to skip the boring bits.

to this day, if I have abandoned a book, it takes me ages to admit it. the book will sit around taunting me. I'll read magazines or the internet and go bookless until I have to sort of sit myself down and go "you're not gonna finish that book. admit it." last year was a bad year for this & 2008 isn't shaping up too good 'cause it's now been a week since I touched Auto-da-Fe. Damn German writers with their crazy dwarves and stuff.

I'm still wondering if I'm going to finish Oscar Wao. I did finally get back into The Rest is Noise though. I think I'm finding it gradually more interesting as it goes because I never really cared that much about Wagner or Strauss.

One answer to original question: when library screen says "This item may not be renewed."

This is a horrible confesion but... for me it's easier to know when to stop reading "literature" than it is to stop READING.
I just had my eyes tested and not only do I have unusually large pupils but I should wear reading glasses because i have a tendency to, basically, go cross eyed while reading.
That's because I will read the ingredients on a bottle of Drano if I am bored. In the dark.
My eye doctor said I should control my reading!

I, literally, do not know when to stop reading.

However, I have stopped reading after five to ten pages of a few books.

I tend to slog through more now than in the past. Actaully was completely bored and turned off by the book I am currently reading until about 180 pages in(!) then it suddenly started cracking. So it took me two weeks to slog through the first 180 pages and I've torn through the next 180 pages in the last day or so - so I'm glad to have stuck with it, in this rare case...

I don't feel bad about giving up on a book though - it's just hard to do, because I keep thinking I want to know what's in this thing...

I have bailed out of The High Cost of Free Parking. I knew the moment had come when the author admitted to wanting to title it Aparkalypse Now (around page 8).

Still, it had a cute cover.