The difference between a book and a monitor is that when you are reading on a screen, your eyes can't scan smoothly and accurately (and quickly) back to the beginning of the line of text you've just read, so that you can read the next line. Your eyes could manage that feat easily if you were reading a book, because the book is always there, but it's not so simple when you're reading on a screen. The reason for this is that when you are looking at a screen you are looking at the equivalent of a movie made up of flashing still images that interrupt much longer periods when there's no image at all. None. As I'll detial later, this is not just of cathode ray tubes, but its of devices using alternating current generally. Don't be to sure your LCD screen is better.
Swing your eyes very rapidly back and forth from one side of a movie screen while your're watching a flick and you'll notice that it breaks up into separate and confusingly overlapped images. (So we learn not to do that, and get a bit of a glassy stare at the movies or in front of the tube.) Same with a computer screen. You can't easily follow a line of text backwards on a computer screen at a good speed because it literally isn't there most of the time that your eyes are moving - your brain gets two or three disjointed images as your eyes try to swing back to the start of the next line, at most. Trying to slowly and carefully follow these disjointed images so precisely as to get to exactly the next line without any external clues (such as a paragraph ending) to help you, really can give you a headache.
If so, your headache comes in part from straining the eye muscles to hold the eyeball extremely steady (literally.) It always takes a lot more individual muscles to move precisely than to move easily and sweepingly, and some of those muscles will have to be tensed in opposition to others. Since many of these muscles are rarely used otherwise they may complain or it may require a lot of mental effort to control them. Then again, you may just find the extra time it takes to your place at the beginning of each new line annoying.
So that's where paragraph breaks come in. On the net, we use them (albeit unconsciously for the most part) to reorient ourselves and find the next line as we read. But if what we are reading is a long sentence in the middle of a screen long paragraph, just try to read quickly and you're lost. Repeatedly. Even trying to stay on exactly the same line may be difficult. This is because you can't count down from the paragraph's start, or up from its end. The ends of the paragraph are outside your fovea's range, so you'd have to shift your eyes, losing the line you were on, anyway.
There was a time when publishing was in it's infancy, and fewer people were literate when the problem of keeping one's place was taken much more seriously. We've all heard the word "catchword" but may not know where it comes from. In earlier days, in order to help readers keep their place between pages, a "catchword", namely the first word of text on the following page, was printed in the lower right-hand corner of every page of a book. (Then again. there was a time when the Greeks didn't use spaces between words to help readers out a little.) Since monitors have made reading a bit more difficult, it's helpful to aid the reader a bit more again in keeping their place.
The most conservative rule of thumb is probably to make sure that every line of text is within four lines of the start or end of a paragraph - which means that more than eight lines for a paragraph may actually be too many, and sixteen are - on a computer. The degree to which you can move your central vision processing power (or focus of attention) away from the point where your fovea is actually looking, may change this, making larger paragraphs quite readable. However, most people don't even know this can be done, and won't find it an easy skill to pick up, particularly if they aren't frequent lucid dreamers. It's probably kindest to be conservative, therefore, and write for those who haven't developed any siddhis, or aren't wholly comfortable reading ofv monitors.
Admittedly LCD screens are a bit better than cathode ray tubes in regard to display persistence, but only modestly so. Because greater image persistence would cause "smearing" of the pointer, or of objects moving in a game, manufacturers generally opt for higher refresh rates and also the lowest possible image persistence - which is actually bad for reading. Maybe someday, on non-cathode-ray-tube screens, you'll be able to adjust image persistence so that it's more like a book when you're reading. Maybe they'll make the screens smarter so that they adjust themselves, and provide near-continuous image persistence when the image is static in any case, or when the screen contents show that you're just reading (anybody got money for a patent?) Until then, break up the paragraphs, baby. Eight to sixteen lines at most, most of the time.
That or we could all snap up those ancient monitors with cheap green phosphors on which you could watch the letters sloowwwlllyy fade away after you unplugged them.
Don't be too sure your wonderful LCD screen doesn't flicker at all: remember that alternating current is off and on. It's true that many devices "correct" AC current by transforming ot into direct current - but this almost always alters only the direction of the current, not the fact that that current is intermittent. Devices that remove the intermittency exist but are much rarer. But in any case, we don't all have fancy LCD screens yet. If nothing else, have mercy on those of us too poor to upgrade yet.
I should mention that there are other solutions to this problem that are used elsewhere on the net: one common one is to revert to a "broadsheet" style of presentation using very narrow columns. This makes the job of scanning back to the beginning of the next line much easier, which is why is was popular to begin with in much less literate times; it wasn't just a fashion statement then, and it isn't on the web, now.
Another method is to make every fourth or fifth line of text a distinctly different color, or to slightly bold it to get a similar effect, providing the equivalent of graph paper for text readers, or go down a line and a half instead of just one line. But this hasn't caught on everywhere yet and might make you feel too much like a four-year-old. It would be pleasant if your OS or browser offered this periodic bolding or coloring as an option you could toggle on if desired. Then again, as the Russians say, "If my Grandmother was an omnibus, I'd ride into town for free."
I admit, this new tradition of shorter paragraphs somewhat undermines the old semantic purpose of dividing text into sections of uniform meaning. But until the
headaches flickering decreases, we'll all just have to live with that. Perhaps you could bold the first three words of every bigtime semantic paragraph break, if you want to demonstrate visually that your writing is even more coherent than it appears, or use an html break to create subparagraphs that don't represent semantic breaks, if you really hate the idea of very frequent paragraph breaks.
In summary, sometimes technology adapts to us, sometimes we have to adapt to technology. For now, we're in one of the latter times.
Written for my sins. (in an earlier version of "Little Bubble Worlds" especially.)
First posted Jan 30 2004 or earlier
Last revised July 9, 2004