Should book text be justified or left aligned?

Justified is the convention for printed prose, and it is what almost every novel on a shelf uses. Left aligned is correct for lists, poetry, definitions and captions, where line breaks carry meaning, and it is a defensible choice for a narrow measure where justification would stretch spaces too far.

Why does my justified text have big white gaps?

Because hyphenation is switched off. Justification works by stretching or compressing the spaces between words until the line reaches the full measure. When no word can be broken at the end of a line, all of that adjustment falls on the spaces, and a line with few words has few spaces to absorb it.

What is a river in typography?

A pale channel of white running vertically down a paragraph, formed when wide word spaces on consecutive lines happen to align. It is a symptom of over-stretched justification, and once you have seen one you will see them constantly in books set without hyphenation.

How many consecutive hyphens are acceptable?

Two is the usual limit in book typography, and three is the outside maximum. A stack of hyphens down the right edge of the text block is called a ladder, and it draws the eye exactly as much as a river does. Most typesetting systems let you set this limit directly.

Should hyphenation be on for headings?

No. Headings are short, they are read as units, and a broken word in a chapter title looks like a defect. The same applies to poetry, where the line is the text and breaking a word the poet set whole changes it, and to lists and definitions where line breaks already carry meaning.

Does hyphenation matter in an ebook?

It matters more, because the reader controls the type size and the screen width. A narrow phone screen at a large type size produces very few words per line, which is the worst case for justification. Many reading systems hyphenate automatically for exactly this reason.

What is the ideal line length?

Between 60 and 70 characters including spaces is the conventional target for continuous prose. Below about 45 characters, justification starts to fail regardless of hyphenation, because there are too few word spaces on a line to absorb the adjustment invisibly.

Why justified text needs hyphenation

Justified text is the default in printed books, and it is worth knowing what the machine is doing to achieve it, because the most common typographic defect in self-published books comes directly from misunderstanding it.

What justification does

A justified line has to reach the full measure exactly. The typesetter sets words on the line until one will not fit, and then something has to give, because the line is now slightly too short.

The engine has three instruments:

Stretch the word spaces, so each gap widens slightly.
Compress the word spaces, if the line is slightly too long and squeezing is less ugly than stretching.
Break a word at the end of the line and carry the rest over, which requires hyphenation.

Take away the third instrument and the entire adjustment falls on the first two. That is the whole mechanism, and it is why turning hyphenation off does not remove the problem — it relocates it into the spaces, where it is less obvious to describe and far more visible to read.

Justification is a fixed amount of error looking for somewhere to go. Hyphenation gives it a second place to go.

Rivers

When word spaces stretch on several consecutive lines, the wide gaps sometimes line up vertically. The eye joins them into a pale channel running down the paragraph, and typographers call it a river.

Rivers are distracting in a way readers cannot name. The eye is drawn along the vertical white instead of across the horizontal text, and reading slows fractionally on every affected paragraph.

They are also, once you have noticed them, impossible to stop noticing. Open any self-published paperback with justified text and no hyphenation and you will find them within two pages.

The arithmetic of a narrow measure

The severity depends on how many word spaces a line has to absorb the adjustment.

A line of 70 characters has roughly 12 word spaces. If the line needs 12 points of extra width, each space grows by one point, which is invisible.

A line of 40 characters has roughly 7. The same 12 points means each space grows by nearly two, which is not invisible at all. And a line with one long word in it — a name, a technical term — can have three or four spaces carrying the entire adjustment.

This is why the conventional measure of 60 to 70 characters is not merely about eye travel. Below about 45 characters, justification starts to fail structurally, because there are not enough spaces on a line to hide the correction.

A book set at a narrow measure — a 5 × 8 trim with generous margins, or a two-column layout — is a book where justification needs hyphenation most, and where authors most often turn it off because the hyphens are more visible.

The other failure: ladders

Hyphenation has its own defect. When several consecutive lines end in a hyphen, they form a stack down the right edge of the text block, which is called a ladder.

A ladder draws the eye exactly as a river does. The conventional limit is two consecutive hyphenated lines, three at the very outside, and any typesetting system worth using lets you set that limit rather than leaving it to chance.

Two other conventions worth keeping:

Do not hyphenate the last word of a paragraph.
Do not hyphenate across a page break, so the reader does not have to turn the page to complete a word.

Where hyphenation should be off

Justification and hyphenation belong to running prose. They do not belong everywhere.

Headings. Short, read as units, and a broken word in a chapter title looks like a defect rather than a decision.

Poetry. The line is the text. Breaking a word the poet set whole changes the poem, and justification stretches a line to a width the poet did not choose.

Lists and definitions. Their line breaks already carry meaning, so imposing a second system of breaks on top competes with the first.

Captions and short columns. Too narrow to justify well, and short enough that ragged edges are not noticeable.

The general rule: prose that runs for many lines is justified and hyphenated. Anything whose line breaks mean something is set ragged and unhyphenated.

Language matters

Hyphenation is language-specific. The rules for breaking English words differ from German, French or Spanish, and applying English patterns to another language produces breaks that are simply wrong.

If your book has passages in another language, the text needs to be marked as that language so the engine can apply the right patterns. This is the same declaration that makes an EPUB accessible, so it is worth doing regardless.

What to actually do

Leave justification on for body prose. It is the convention and it looks right.
Leave hyphenation on with it. The two are one decision, not two.
Cap consecutive hyphens at two.
Turn both off for headings, verse, lists and captions.
Aim for 60–70 characters per line, and be more careful the narrower you go.
Mark the language of any passage that is not in the book’s main language.

The reason this matters more than it sounds is that both defects are invisible while you write and obvious once the book is a physical object. Nobody notices good justification. Everybody feels bad justification, and almost nobody can say what is wrong with it.

In Nueel, alignment and hyphenation belong to the design’s text styles rather than to individual paragraphs, and the slots that should never inherit them — verse, lists, definitions, headings — carry their own shape instead. So a book set justified does not quietly justify its poetry, and a change to the body does not have to be undone in six other places.

Common questions

Should book text be justified or left aligned?: Justified is the convention for printed prose, and it is what almost every novel on a shelf uses. Left aligned is correct for lists, poetry, definitions and captions, where line breaks carry meaning, and it is a defensible choice for a narrow measure where justification would stretch spaces too far.
Why does my justified text have big white gaps?: Because hyphenation is switched off. Justification works by stretching or compressing the spaces between words until the line reaches the full measure. When no word can be broken at the end of a line, all of that adjustment falls on the spaces, and a line with few words has few spaces to absorb it.
What is a river in typography?: A pale channel of white running vertically down a paragraph, formed when wide word spaces on consecutive lines happen to align. It is a symptom of over-stretched justification, and once you have seen one you will see them constantly in books set without hyphenation.
How many consecutive hyphens are acceptable?: Two is the usual limit in book typography, and three is the outside maximum. A stack of hyphens down the right edge of the text block is called a ladder, and it draws the eye exactly as much as a river does. Most typesetting systems let you set this limit directly.
Should hyphenation be on for headings?: No. Headings are short, they are read as units, and a broken word in a chapter title looks like a defect. The same applies to poetry, where the line is the text and breaking a word the poet set whole changes it, and to lists and definitions where line breaks already carry meaning.
Does hyphenation matter in an ebook?: It matters more, because the reader controls the type size and the screen width. A narrow phone screen at a large type size produces very few words per line, which is the worst case for justification. Many reading systems hyphenate automatically for exactly this reason.
What is the ideal line length?: Between 60 and 70 characters including spaces is the conventional target for continuous prose. Below about 45 characters, justification starts to fail regardless of hyphenation, because there are too few word spaces on a line to absorb the adjustment invisibly.