Ligature Usage

Posted on 2026-Jul-15 at 16:40:00 by Phil

When should ligatures be used?

History of ligatures

Ligatures are “combined” sets of 2 or more letters into a single glyph or piece of type. They originated because lowercase f’s often had the “hook” (the little overhanging tail at the top) left unsupported by the slug’s main body. They were intended to overhang the next letter’s main body, which would support them as the slug was pressed against paper.

Unfortunately, this overhang left the hook as being fairly fragile, and it was not uncommon for it to be snapped off, requiring that the entire slug be tossed into the scrap heap to be melted down and recast. A solution was developed to take care of the most common combinations of f followed by a “tall” letter, of ff ff, fi fi, fl fl, and extensions of ff: ffi ffi and ffl ffl. These were designed and cast as single slugs, and often featured the letters moved slightly together until they touched. For fi, the hook and tittle (i’s dot) were often merged, to either prevent a collision and fracture, or to avoid having a dot very close to a rounded hook end.

Unicode includes these five ligatures as code points (U+FB00 through U+FB04), plus ft and st (U+FB05 and U+FB06), although the latter two are more in the vein of common stylistic decorative flourishes than useful in keeping slugs from breaking. Some Latin alphabet letters might be considered (or were originally) ligatures, such as ss/sz/eszett ß (and in some fonts, its capital form), tz/TZ, ash æ and Æ, and oe/OE œ and Œ. Some fonts offer ij/IJ ij and IJ, and fj fj as ligatures. Various fonts have been seen with ct and tt ligatures, although these are usually just stylistic (i.e., decorative). Although they are separate Unicode codepoints, simply accented letters (e.g., a + acute accent á) are normally not considered ligatures.

Application of ligatures

In “cold metal” typesetting, where a compositor hand-picked letters out of a bin and assembled them into lines, breakage of certain characters (especially f) was a constant problem, and the use of various ligatures for f was welcome relief. Later “hot metal” typesetting (e.g., MonoType and LinoType machines) may not have had so much of a problem with their molds, but carried on the tradition anyway of providing ligatures. Modern printing methods, frequently using laser or ink jet printers (as at least the first step for something like photolithography), have no concerns of type breakage. Nevertheless, tradition dies hard and many computer fonts still offer various ligatures, because people expect to see them in fine typesetting.

Many users of typesetting or word processing systems are blissfully unaware of the existence of ligatures, and simply type in the sequence of letters (with the common exception of eszett as its own character on German keyboards/Western European encodings). Some display and printing systems will automatically form ligatures out of letter sequences, if available in the font used. The HarfBuzz system can do this. Many systems simply print the sequence of letters “as is” and the result, while perfectly readable, is often not considered “high quality” typesetting.

On the other hand, users should be aware of problems if they explicitly enter ligatures into their original source. One is that a given font may not include that particular ligature, even if it is a valid Unicode (or some other encoding) code point. If they’re lucky, it will simply be rendered as the sequence of letters, if the system knows enough to make the substitution. Another problem is that when using a different editor or word processor, a ligature may display oddly (e.g., as an HTML entity, as a hex code, as a gibberish character sequence, or something else, depending on how it was encoded). A more serious problem comes when some sort of “uppercasing” needs to be done, such as for titling and such applications, or for Small Caps or Petite Caps transformations. Many systems do not know how to capitalize lowercase ligatures (or, conceivably, do the reverse) and will leave the original lowercase ligatures “as is” in the text, while the rest is capitalized. While technically still readable, this looks bad.

Restrictions on using ligatures

Now that fonts have provided us with a set of ligatures (at least the basic five, in almost any font), the issue is cut and dried, right? Wherever you have a certain sequence of letters, you can just automatically replace them with a ligature (if available), and that’s that. Well, not quite.

At least in the English language, there are rules you are supposed to follow when subsituting ligatures for sequences of letters. The primary one is that ligatures should never cross morpheme boundaries. That is, a ligature should never be used to tie together the end of one morpheme and the beginning of another. The definition of a “morpheme” seems a bit nebulous, but it seems to be the basic parts of a word — the core or base or stem, and any prefixes and suffixes, each of which is a somewhat independent component (“smallest meaningful constituent”) with its own grammatical meaning. Do not confuse morphemes with syllables — they are not interchangeable terms. An example: stiffly consists of the adjective stiff plus the adverb-forming suffix ly. According to this rule, you should not use the ffl ffl ligature (“stiffly”) because that will tie together the two morphemes (and syllables). This is considered bad because it may confuse a reader as to the formation, and thus the meaning, of the word, as well as its pronunciation (as the syllable separation has been slightly damaged).

Where does this leave us?

Well, the morpheme rule above, at best, greatly increases our labor to produce text. You can’t simply turn the computer loose on a bunch of text and let it replace all of certain sequences by ligatures (even if the font supports those ligatures). You have to go case-by-case and decide which ligature, if any, can be used in each individual case (unless you’ve got a really smart typesetting system!). It’s almost not worth the bother.

My take on this is, if font designer (whether centuries or months ago) decided to include ligatures, they should be used consistently or not at all. After all, in the bad old days of cold metal type, the use of ligatures could eliminate the massive breakage of certain letters — that was their whole reason to exist! I would presume that they were always used. The sentence, “He sat stiffly as he ate his waffles,” could use ligatures “properly” per the morphemes rule: “He sat stiffly as he ate his waffles," or consistently: “He sat stiffly as he ate his waffles.” It’s not the (small) space-savings that’s of interest, it’s the consistent appearance of the text that concerns me. In fact, I think my browser may be trying to outsmart me and substitute ffl for ffl in these cases anyway (whether or not I explicitly broke them up into ff-l or f-fl)!

What do others do about this issue?

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Last updated Wed, 15 Jul 2026 at 4:40 PM

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