Ligatures, kerning and small caps
A page can have the right face, the right size and the right margins and still read as a document rather than a book. What is usually missing is a set of details so small that no reader will ever name one of them.
They are worth understanding anyway, because two of the three are decided by your software rather than by you, and one of them can quietly break your file.
Ligatures: two letters drawn as one shape
Some pairs of letters collide. In most serif faces, the ball at the end of a lowercase f runs straight into the dot of a following i, or into the ascender of an l. Left alone, the result is either a visible crash or an awkward gap where the setter has pushed them apart.
A good face solves this by drawing a single character for the pair: fi, fl, and the three-letter forms ffi and ffl. The f gives up its terminal, the i gives up its dot, and what prints is one shape with the spacing built into the design rather than negotiated at setting time.
At display sizes this is a refinement. At book sizes it is the difference between a clean word and a blot. Ink spreads slightly on uncoated paper, so a collision that merely looks tight on screen prints as a dark clump at 11 points, and fi appears a few hundred times in any English chapter. The effect is cumulative and invisible: the page just looks slightly dirtier than it should.
Some faces also draw decorative ligatures — st, ct — which belong on a title page, not in body text, where they stop a reader mid-sentence.
The ligature trap that breaks your file
Here is the part that matters more than the typography.
A ligature is a separate character in the font, with its own internal code. When that character is placed in a PDF, the file has to carry a note saying that this shape means the two letters f and i. If that note is missing, the PDF looks perfect and behaves badly: searching the file for "final" finds nothing, and copying a paragraph out gives you text with holes in it where every fi and fl used to be.
This is not a hypothetical. Some export tools ship the defect, and it survives into the file you upload, where a reader searching your book — or an accessibility tool reading it aloud — hits the gap. It matters most in nonfiction and reference.
You can test any PDF in ten seconds. Open it, search for a word containing fi or fl — "find", "flow", "difficult" — and see whether it is found. Then copy a paragraph into a plain text editor and read it. If letters are missing, the file is defective whatever it looks like on screen.
In the Interior Formatter. Pair kerning and ligatures are applied by default, and every ligature is mapped back to its plain letters in the exported PDF, so search and copy return the words you actually wrote. Start a book → · about the Interior Formatter
Kerning: fixing the pairs that look wrong
Every letter in a font carries its own side bearings — a bit of built-in space on the left and the right. Those work for most combinations and fail badly for a few.
The classic failures are pairs where an open shape meets a closed one. AV and AW leave a wedge of white between the diagonals. To, Ta and Ye leave the lowercase stranded under the arm of the capital. A period after a y, a lowercase o after a V — all produce a gap that reads as a space when it is not one.
Kerning is the correction: a table inside the font listing specific pairs and how far to close or open them. A well-made book face has thousands of these pairs, and applying them is the difference between a title that looks set and one that looks typed.
Kerning is not tracking. Tracking adds or removes space uniformly between all letters. The two get confused constantly, and the distinction is practical: kerning fixes a fault, tracking changes a texture.
The rule for body text is short. Do not track body text to fix a page. Tightening a paragraph to pull up a widow works, and it is a last resort, because it changes the color of that paragraph relative to every other paragraph in the book. A reader will not know what they saw; they will see that one block is darker. Rewrite a sentence instead. See Widows, orphans and rivers: the faults readers feel.
Tracking has legitimate uses, and they are all at large or all-capital sizes. Capitals are drawn to sit beside lowercase, so a line of them looks cramped without a little extra space added. That is why running heads set in capitals or small capitals are letterspaced.
Small caps: drawn, not shrunk
A real small capital is a capital letter designed at roughly the height of the lowercase, with its stroke weights and proportions redrawn to match. It is a separate set of characters in the font.
What most software gives you instead is the full capital scaled down. The strokes scale with it, so the letters come out too light and too narrow, and they sit next to the surrounding text looking anemic. Side by side the fake is obvious; on its own it just looks weak, which is worse because you will not know why.
Where small caps belong:
- The first few words of a chapter. Setting the opening two or three words in small capitals is a quiet way to start a chapter. See Parts, sections and the pages between chapters.
- An author's name on a title page, where full capitals would shout.
- Acronyms in running text. NASA, FBI and BBC set in full capitals punch holes in a paragraph. In small capitals they sit at the weight of the text around them.
- Running heads, letterspaced.
Where they do not belong: whole sentences, headings you want people to read fast, and anything where the reader needs to pick out proper nouns quickly.
The practical consequence is a font choice, not a setting. If your book uses small capitals anywhere, choose a face that has real ones before you typeset, not after. See Choosing a typeface for the body of a book.
In the Interior Formatter. All six body faces have a true italic, and pair kerning, ligatures and letterspaced running heads come through in the exported print PDF. Start a book → · about the Interior Formatter
Make yours
Everything here is built into the tools, and they are free to use: name your book, bring your manuscript or your artwork, and work as long as you like. You only pay when you want the files without the preview watermark.
Next: Running heads and page numbers · Back to Justification, hyphenation, and the gaps between words · Also: Choosing a typeface for the body of a book · Preflight: what to check before you upload