(Edited for typos and to hand-tweak the typography. See new appendix at bottom.)
Are there any rules or standards telling me when I should use a ligature and when I shouldn’t?
In version 3.2 of Robert Bringhurst’s The Elements of Typographic Style (Hartley & Marks, 2008), the main discussion of ligatures occurs on pages 50–53, under the section ‘3.3 Ligatures’, which has two subjections I shall describe below. Signiﬁcant mentions of ligatures also occur at perhaps a half-dozen other points in this book.
This is one text that truly cannot come too highly recommended. If you do not own it, you should. It comes in both trade-paper and hardcover editions. Buy it. No scanned version is available via Google Books, and it is unlikely that it ever shall be — for reasons that should become quickly apparent once you crack its spine. The hardcover has a sewn binding with a built-in red silk bookmark, and costs only $10 more than the trade paper; seems worth the upgrade to me. But both bindings are remarkably well-made books. Just make sure to get the most recent version; as of this writing, that is version 3.2 from 2008.
The ﬁrst subsection of ‘3.3 Ligatures’, which is on page 50, is entitled:
3.3.1 Use the ligatures required by the font, and the characters required by the language, in which you are setting the type.
In most roman faces the letter f reaches into the space beyond it. In most italics, the f reaches into the space on both sides. Typographers call these overlaps kerns. Only a few kerns, like those in the arm of the f and the tail of the j, are implicit in a normal typefont, while others, like the overlap in the combination To, are optional reﬁnements, independent of the letterforms.
Reaching into the space in front of it, the arm of the f will collide with certain letters – b, f, h, i, j, k, l – and with question marks, quotation marks or parentheses, if these are in its way.
As the craft of typography spread through Europe, new regional ligatures were added. An fj and æ were needed in Norway and Denmark for words just as fjeld and fjord and nær. In France an œ, and in Germany an ß (eszett or double-s) were required, along with accented and umlauted vowels. Double letters which are read as one – ll in Spanish, ij in Dutch, and ch in German, for example – were cast as single sorts for regional markets. An ffj was needed in Iceland. … Purely decorative ligatures were added to many fonts as well.
If your software is inserting ligatures automatically, take a moment to verify two things: (1) that the software is inserting all the ligatures you want and none that you do not want; (2) that all these ligatures are staying where they’re put.
That goes on for quite some time, and is important. I’ll try to summarize all this below instead of typing it all in. The other subsection, which isn’t until page 52, is entitled:
3.3.2 If you wish to avoid ligatures altogether, restrict yourself to faces that don’t require them.
It is quite possible to avoid the use of ligatures completely and still set beautiful type. All that is required is a face with non-kerning roman and italic f – and some of the ﬁnest twentieth-century faces have been deliberately equipped with just this feature. Aldus, Melior, Menoza, Palantino, Sabon, Trajanus and Trump Mediäval, for example, all set handsomely without ligatures. Full or partial ligatures do exist for these faces, and the ligatures may add a touch of reﬁnement – but when ligatures are omitted from these faces, no unsightly collisions occur.
As always in Bringhurst, you should pay careful attention to the thoughtful and revealing sidenotes in this section. They contain myriad wonderful examples of typefaces and effects that are completely impossible to reproduce here. It’s much too much for me to type in, but do please read it. Here’s just one from page 51:
Decorative ligatures such as ﬆ and Th are now deservedly rare. The ligature ffﬂ is rarer still, but it has been cut for at least one typeface(Jonathan Hoeﬂer’s Requiem italic).
What I will type in in toto, however, is the deﬁnition from the glossary from page 312:
ligatures Basic ISO fonts are limited to typographic ligatures, ﬁ and ﬂ. Rigid deﬁnitions of the glyph set, leaving no provision for additional
ligatures (such as ff, fﬁ, fﬂ, fj) are a hazard to typography. Ligatures required by the design of the individual typeface should always reside on the basic font.
The lexical ligatures ligatures æ, Æ, œ, Œ and ß are bonaﬁde Unicode characters, separately listed in this appendix. Typographic ligatures such as ﬁ and ﬆ are glyphs, not characters, but many are now included in Unicode as “presentations forms.” [U+FB00—FB06]
When Bringhurst writes ‘glyph’ above, he means what a hand compositor would call a ‘sort’: something that would have its own slot in the compositor’s case. Most (but not all) digital fonts are distressingly impoverished when it comes to glyph variants. For his 42-line Bible, Gutenberg needed perhaps 40 sorts; he used 290. That tells you how important they are.
However, you should not encode attempt to encode any typographic ligatures into your text, even for those few for which Unicode code points exist. (Edit: but see the bottom of this posting for why I have been forced to do so here.) Rather, this is something that must be done for you automatically by your typesetting software. You may be able to enable or disable such implicit selection, or distinguish between basic (typographic) ligatures and discretionary (typographic) ligatures.
Here are several discrete font suggestions with good typographic ligatures:
One Western (Latin, Greek, and Cyrillic) OpenType face particularly rich in typographic ligatures, and which also includes the best Unicode support (highest number of glyphs, including many variants) seen to date, is Richard Slimbach’s Arno Pro, released in 2007. Slimbach is also the designer of Minion and Poetica. I can’t begin to describe how nifty this font is. (Well, I suppose I could, considering that I have an entire 19-page write-up of it which still only barely scratches the surface. But I have no space for that here.) It is based on early Renaissance forms, and is quite possibly already on your computer, as it was included with Adobe’s CS3. If you like fonts cut by Claude Garamond (or Garamont), Robert Granjon, or Jean Jannon, then you will like Slimbach’s Arno Pro.
For typographic ligatures in general roman and italic faces, little can compare with Zuzana Ličko’s lavish Mrs Eaves (1996), which sports some 71 typographic ligatures. It is based on (the original) Baskerville. That’s for basic Latin, though. It does not have anything like the Unicode support that Slimbach’s much more recent Arno Pro offers.
For script faces, master punchcutter and designer Hermann Zapf ’s Zapﬁno and its OpenType version, Zapﬁno Extra (2004), are without peer. In Zapﬁno, the very word Zapﬁno is itself a ligature, and comes with several outstanding variants. There really is no other font like Zapﬁno; Bringhurst calls it a calligraphic tour de force: “It is an exemplary marriage of artistic and technical ability. Effective use of such a type requires considerable patience and skill.”
For Greeks, Matthew Carter’s Wilson (2005) is highly recommended. Like Zapﬁno, Wilson is sui generis. It is an exceptionally well-cut chancery Greek, which means it is highly embellished, full of elaborate ligatures and alternate forms. In this it is reminiscent of Robert Granjon’s chancery Greek that he cut in the 1560s, but Wilson gets its name from the fonts it is more directly based on, those of the eighteenth-century master, Alexander Wilson of Glasgow, who was also an astronomer and a physician.
Those fonts I’ve listed above all handle typographic ligatures exceptionally well. But as I’ve said, you should not encode typographic ligatures in your own text. (Edit: But see the bottom of this posting for why I’ve been forced to do so here.) That is for the font to decide for you. See also the Unicode FAQ on Ligatures, Digraphs, and Presentation Forms, and take especial note of this answer:
A: The existing ligatures exist basically for compatibility and round-tripping with non-Unicode character sets. Their use is discouraged. No more will be encoded in any circumstances.
Ligaturing is a behavior encoded in fonts: if a modern font is asked to display “h” followed by “r”, and the font has an “hr” ligature in it, it can display the ligature. Some fonts have no ligatures, some (especially for non-Latin scripts) have hundreds. It does not make sense to assign Unicode code points to all these font-speciﬁc possibilities.
However, you should deﬁnitely let the font use them if they are needed in that font. It’s the same as with kerning. If the font needs it to avoid collisions, you must use it or else use a different font; see the second of Bringhurt’s ligature subsections.
For example, in Georgia (which I believe you are reading this in right now), you cannot write things like f ’ and f ” without unacceptably horrible collisions producing f’ and f”. That’s just one reason web pages, even this one, frankly look like crap. Fonts designed with typographic ligatures and kerning in mind cannot be acceptably used without them.
Lastly we come to lexical ligatures. Here the story is quite different. There are absolutely required by the language. For example, the name of famed Icelandic programmer Ævar Arnfjörð Bjarmason cannot be written any other way. Writing *AEvar or *Aevar would simply be wrong. In the same way, if you were talking about the Old English word that became modern wrath, you would have to write wrǽððu or wrǽþþu (both were known to occur). Similarly, French words and phrases like un œuf, hors d’œuvres, and ma jolie sœur are not supposed to be written broken up; it is highly frowned upon in French. The Encyclopædia Britannica actually has that lexical ligature in its registered trademark, and so must be maintained. And IPA uses both œ and ɶ (the small caps version) to mean separate vowels; you mustn’t mess with those. All those are lexical ligatures.
For other cases in English, the style has largely shifted, although it does still depend to some degree on the publication and nation of origin. Where we once wrote œnophile and amœba, Cæsar and archœology, we tend now to write those with the letters ‘broken apart’, so to speak.
My own recommendation is to use lexical ligatures if you are quoting another source that uses them, especially if they are originally in another language than English, or, if in English, you are trying to reproduce the original. This is the same rule of thumb used for diacritics.
For example, in a poem written in honor of the 19th centenary of Virgil’s death, Alfred, Lord Tennyson wrote such lines as Thou that seëst Universal / Nature moved by Universal Mind alike with Now thy Forum roars no longer, / fallen every purple Cæsar's dome— and you would be remiss not to reproduce those as the poet wrote them. Similarly in Lord Byron’s Episode of Nisus and Euralyus when he wrote Yet wakeful Rhæsus sees the threatening steel or When great Æneas wears Hesperia's crown.
If the original had them, then you likely should, too.
However, I dare say that maintaining those historical forms when writing your own new material upon Caesar or Aeneas is a bit too precious. There’s a reason that some ligatures get called ‘quaints’ by typesetters. You might not care to appear so quaint.
Then again, perhaps you might. It’s really up to you.
Because ELU is presented to us in Georgia, I have hand-tweaked some of the typesetting, because with extremely rare exception, web browsers are far too stupid to use the mandatory ligatures and kerns that are absolutely required with this font.
I have therefore actually used the only three Latin typographic ligatures that Georgia provides: ﬁ for fi, ﬂ for fl, and although it appears to be unnecessary, ﬀ for ff. Only the first of those appears to have been strictly necessary for this font, and so it is a bug that browsers don’t do it.
I have also in several places hand-kerned the f so that a following quotation mark, single or double, no longer collides with it. I have done this by placing a U+200A hair space after the f and before the quotation mark, making f’ ﬁnally correctly render as f ’, and f” as f ”.
I should not have to do these things, but web browser technology is extremely primitive when it comes to typography. Gutenberg was far superior to anything we have yet achieved in web browsers, which means that we have still not caught up to the very ﬁrst instance of movable type of almost half a millennium ago; pretty sad, isn’t it? However, browser awareness of OpenType hinting is apparently coming, at which point all this silliness should no longer be needed.
I’m sure Georgia is used here because it is the only universally available font that by default uses text ﬁgures instead of titling ﬁgures, as is of course properly done. Unfortunately, Georgia is also one of those fonts that cannot be correctly rendered without typographic ligatures and kerning hints being automatically applied — which is why I’ve been forced to make the various hand adjustments described in this edit.
Unfortunately, Georgia does not have very good Unicode support at all, nor does it have small caps, which are also required for tolerable typesetting.