Uneven word spacing in justified Latin runs creates rivers

What it is

Latin justification stretches the spaces between words until a line fills the column. Those spaces become unequal. When wide gaps on neighbouring lines line up, the page grows a pale river. This is not uneven tracking — the seams inside letters are untouched — it is word spacing used as elastic. A river pulls the eye off the line and down the white fissure, as if the paragraph had been torn.

Why it happens

A justification engine’s main degree of freedom is the word space; letter-spacing tweaks and hyphenation come after. In a narrow column there are few words per line, so leftover width lands on two or three spaces and each one is pulled wide. If the next line happens to park a wide space at a similar horizontal position, the white joins vertically. Narrower columns, lazier hyphenation, fewer soft hyphens: stabler rivers. Chinese justification mostly compresses punctuation and em-box seams; it has almost no word spaces to stretch, so this hole is a Latin-paragraph disease, not a disease of “alignment.” Flush-left leaves leftover width at the line end, word spacing stays the face’s constant, and rivers have nothing to form from.

Where it stops holding

A wide column, hyphenation on, and an engine that hyphenates and micro-adjusts will dilute word-space variance until a river is too faint to bother. A two-line pull quote never has time to connect. Justified monospace almost always rivers, because there is no kerning to borrow and all elasticity sits in the spaces. Justification in a narrow column can also stretch letter-spacing until the alphabet looks chewed; that is a separate failure. This claim only names the vertical white made of word spaces.

Applying it

• Prefer flush-left for Latin body. If you must justify, give the column about fifty to seventy characters and turn hyphenation on.
• Print the paragraph or capture a tall screenshot and squint: does a white fissure run through three or more lines? If it does, widen the column, allow hyphens, or return to flush-left.
• Do not open tracking to “fill” a river; that splits the words. The river’s material is word spacing, not letter-spacing.

Related

• Same group: F4.12.1 Tracking that is too tight collides glyphs; too loose breaks the word · F4.12.2 CJK usually needs no extra tracking; the em box already holds the gap · F4.12.3 All-caps and small type need extra tracking to stay distinguishable
• Nearby: F4.05 Alignment · F4.03 Measure
• Search terms: rivers · justified type · word spacing