What is a ligature in typography?

A single glyph drawn to replace two or more letters that collide when set next to each other. The common case is f followed by i: the f's overhanging hook runs into the i's dot, so the typeface provides one character where the hook and the dot are resolved. It is a fix for a physical problem that began with metal type and survives because the collision is still there in digital faces.

Should ligatures be on or off in body text?

The standard ligatures should be on, because they solve real collisions in f-combinations. Discretionary ligatures should be off. Butterick's position is stricter than most: turn them on when characters actually collide, and otherwise leave them off, since they can make body text look quaint. For a book the practical answer is standard on, discretionary off, which is what most typesetting defaults to.

What is the difference between standard and discretionary ligatures?

Standard ligatures fix collisions — fi, fl, ff, ffi, ffl. Discretionary ligatures are decorative and optional: ct with a swash joining the two letters, st, sp, and similar historical pairs. Standard ones are invisible when they work. Discretionary ones are meant to be noticed, which is why they suit a title page or a display line rather than 300 pages of prose.

Why do ligatures look wrong in some words?

Because a ligature should not cross a word boundary inside a compound. In shelfful or offhand, the letters that meet belong to different parts of the word, and joining them visually links things the reader parses separately. German typesetting has long treated this as a rule; English practice is less strict, but the effect is the same and the best faces and layout engines suppress the ligature there.

Do ligatures break search or spell-check?

Not when the font applies them. The text underneath stays as ordinary letters and the ligature is a rendering decision, so searching for 'find' still finds it. What does break things is typing the ligature character yourself: a literal ﬁ in the manuscript can confuse spell-checkers, hyphenation and search indexing. Butterick's advice is to never insert them by hand.

Do ligatures survive into an EPUB?

They depend on the reading system and the font it uses. If the reader has switched to their own typeface, your font's ligatures are gone with it, which is fine — the substitute face applies its own. This is one more reason not to type ligature characters into the text: as literal characters they persist even where they no longer make sense.

Ligatures in a book, and when to turn them off

Set the word find in a serif face and look at the join between the f and the i. In most faces the f has a hook that reaches to the right, over the space where the next letter starts, and the i has a dot sitting exactly there. In metal type those two pieces of lead physically collided, and the fix was to cut a single sort carrying both letters with the collision already resolved.

That single sort is a ligature. Digital faces inherit it because the collision is still there.

Ligatures were doing a second job at the start, which explains why early type had so many of them. Gutenberg’s case for the 42-line Bible held something like 290 characters — ligatures, scribal abbreviations, and narrow and wide cuts of the same letter — and a compositor reached for them to tighten or fill a line so the two columns could justify without the gaping word spaces justification usually causes. A ligature was a fitting tool as much as a fix for a clash. Modern engines do that work by adjusting spacing instead, which is why the surviving ligature set is small.

The ones that fix something

Standard ligatures are the f combinations: fi, fl, ff, ffi, ffl. They exist because the f’s hook is the one part of the roman alphabet that habitually invades its neighbour.

These should be on in body text. When they work you do not see them, which is the point — you see the absence of a clash you were never conscious of.

The ones that decorate

Discretionary ligatures are a different proposition: ct and st joined by a swash arch, and various historical pairs. Nothing collides. They are ornament, deliberately visible, and they carry a period flavour with them.

On a title page or a chapter display line, that can be exactly right. Across three hundred pages of prose it becomes a mannerism, and Butterick’s blunt version of the risk is that ligatures beyond the necessary ones can make text look quaint.

The default for a book: standard on, discretionary off. If you turn the discretionary ones on, do it somewhere the reader looks at the type rather than through it.

Where an automatic ligature is wrong

A ligature says these letters belong together. Inside a compound word, sometimes they do not.

Shelfful is shelf plus ful. Offhand is off plus hand. The ff that meets in the middle spans a seam the reader’s eye is parsing, and joining the letters visually welds across it.

German typography has treated this as a rule for a long time, since compounds are constant there. English practice is looser, but the effect does not care about the tradition, and good faces and layout engines suppress ligatures at those boundaries.

This is a rare enough case that it is not worth auditing a manuscript for. It is worth knowing when a word looks subtly wrong on the page and you cannot say why.

Never type them

The ligature glyph has its own Unicode character, and you can insert it directly. Do not.

When the font applies a ligature, the underlying text is still f and i. Search finds the word, the spell-checker reads it, the hyphenation engine breaks it correctly, and a screen reader says it. When you paste in a literal ﬁ, none of that is guaranteed: Butterick’s summary is that manual ligatures confuse spelling checkers, hyphenation engines and search indexers, and cause more problems than they solve.

There is a related import problem worth checking. Text extracted from a PDF often arrives with real ligature characters baked in, because the extraction read glyphs rather than text. A manuscript assembled that way carries hundreds of them. Searching a draft for ﬁ and ﬂ takes a moment and is occasionally alarming.

What this looks like in Nueel

Standard ligatures are on in body text and discretionary ligatures are off, applied by the shaping engine at layout time rather than stored in your text. The characters in the manuscript stay ordinary letters throughout, so the same file exports to EPUB and DOCX with nothing baked in that a different typeface would have to undo.

The useful distinction is between a ligature that solves a collision and one that performs a period. Keep the first, and spend the second where somebody is looking at the letters.

Sources

Matthew Butterick, Ligatures in Practical Typography — mandatory versus optional ligatures, and the warning against inserting them by hand
FinalType, The justification of the Gutenberg Bible — the 290-character case, and ligatures used as a justification tool

Common questions

What is a ligature in typography?: A single glyph drawn to replace two or more letters that collide when set next to each other. The common case is f followed by i: the f's overhanging hook runs into the i's dot, so the typeface provides one character where the hook and the dot are resolved. It is a fix for a physical problem that began with metal type and survives because the collision is still there in digital faces.
Should ligatures be on or off in body text?: The standard ligatures should be on, because they solve real collisions in f-combinations. Discretionary ligatures should be off. Butterick's position is stricter than most: turn them on when characters actually collide, and otherwise leave them off, since they can make body text look quaint. For a book the practical answer is standard on, discretionary off, which is what most typesetting defaults to.
What is the difference between standard and discretionary ligatures?: Standard ligatures fix collisions — fi, fl, ff, ffi, ffl. Discretionary ligatures are decorative and optional: ct with a swash joining the two letters, st, sp, and similar historical pairs. Standard ones are invisible when they work. Discretionary ones are meant to be noticed, which is why they suit a title page or a display line rather than 300 pages of prose.
Why do ligatures look wrong in some words?: Because a ligature should not cross a word boundary inside a compound. In shelfful or offhand, the letters that meet belong to different parts of the word, and joining them visually links things the reader parses separately. German typesetting has long treated this as a rule; English practice is less strict, but the effect is the same and the best faces and layout engines suppress the ligature there.
Do ligatures break search or spell-check?: Not when the font applies them. The text underneath stays as ordinary letters and the ligature is a rendering decision, so searching for 'find' still finds it. What does break things is typing the ligature character yourself: a literal ﬁ in the manuscript can confuse spell-checkers, hyphenation and search indexing. Butterick's advice is to never insert them by hand.
Do ligatures survive into an EPUB?: They depend on the reading system and the font it uses. If the reader has switched to their own typeface, your font's ligatures are gone with it, which is fine — the substitute face applies its own. This is one more reason not to type ligature characters into the text: as literal characters they persist even where they no longer make sense.