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Discretionary ligatures are non-standard ligatures such as:
Atlantica LF: st ct
st and ct in Atlantica LF font

Are they purely visual or is there any other reasoning to back it up? Psychological? Letter-press related? (Did they even exist in times of letterpress printing?)

Related article on Upper & Lower Case Magazine say these are "… more decorative in nature than standard ligature[s] …" But is that all?

Personally, I find them a bit distracting, especially if they're used in long body types. Also it's hard to imagine they would have any practical value in handwriting — at least I draw the letters from top to bottom, and extra ties between letters would disrupt the flow.

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    I think there's really two separate questions here, discretionary v. standard, and why use ligatures at all - see my answer. – e100 Feb 17 '11 at 20:01
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Standard ligatures and discretionary ligatures are features of a particular font, and the notion of discretionary ligatures only dates back to the introduction of OpenType fonts around ten years ago.

The font designer determines that "standard" ligatures should be used to replace certain letter pairs/triples, whereas "discretionary" ones may be used. The automatic application of either can be specified by the end designer in software.

Yes, there are very common ligatures, e.g. fi, but no real standard across typefaces.

The reasons why ligatures exist or are used at all is probably better handled as a separate question.

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  • Not sure why I said "as per your screenshot". Unless there was one at some point... – e100 Nov 27 '12 at 22:41
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Discretionary ligatures, by definition, are intended to not be on by default. Standard ligatures are those that the type designer thought should be on by default.

The particular ligatures shown, the ct and st ligatures, are historical ligatures that date back centuries. They are considered rather archaic now, and would only be appropriate if one wanted an archaic effect.

No research has been done on discretionary ligatures having a benefit other than aesthetic. However, research has been done that shows that typography that is more appealing but not more functional (that is, typesetting that "looks nicer" but has no impact on reading speed or comprehension) have other, more subtle benefits in mood and performance on subsequent tasks.

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  • An answer from a true expert! Would it be fair to say you had at least some input into the implementation Thomas? – e100 Feb 20 '12 at 17:16
  • Is it known why, centuries ago, someone thought adding an arc to st and ct was a good idea? – Anton Sherwood Aug 4 '16 at 5:09
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It's decoration. Used at the discretion of the typesetter.

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  • Do you mean their sole purpose is decoration or are you just stating that they are decorative? – Jari Keinänen Feb 16 '11 at 21:55
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    Both statements are true. It's purely for decoration. There's a line between useful ligatures (reducing copy size, fitting type) and discretionary decorative ligatures. Where the line is will differ from typeface to typeface, designer to designer, project to project. – DA01 Feb 16 '11 at 23:47
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Ligatures were originally created to decrease the amount of time to write something and layout type. There are numerous examples that go back thousands of years, but I think they became most popular with monks making copies of the Bible and later with early presses to reduce the number of type objects being grabbed from type drawers. Advances in press technology reduced their need over time. Now they are just for decoration (and I, for one, hope they never go away).

As for being distracting, I agree that those in the example are distracting, and I wouldn't even call them "true" ligatures. They really ought to just flow into the text, much like really tight kerning between "f" and "i".

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  • Neither I call them true ligatures; in fact, I called them discretionary ligatures and stated them as "non-standard" in the first sentence. You slightly misunderstood my question. – Jari Keinänen Feb 16 '11 at 21:53
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    Perhaps, but I would say these days all ligatures are purely discretionary. They are a dying art. – Philip Regan Feb 16 '11 at 22:15
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    I could agree they are all discretionary, but I wouldn't call them a dying art. With OpenType, we're see a resurgence in faces supporting a wide variety of ligatures. – DA01 Feb 17 '11 at 23:36
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    Without ligatures, typographers would be greatly limited in their designs, especially with elaborate script typefaces. Both normal and discretionary ligatures, as well as alternate glyphs, are important tools in modern typography that greatly expand the flexibility and usefulness of typefaces. – Lèse majesté Feb 20 '12 at 17:23
  • @Lèsemajesté: In actual lead type, I've often seen "Qu" as a ligature, but I don't think I've ever noticed it in a computer font except for things that are supposed to function like dice in the Boggle® brand game. – supercat Jun 17 '14 at 2:55
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Whilst ligatures may have lost much of their original function in modern print, that is to say printing from digital files, they were (and still are) an essential part of traditional letterpress printing - that is, printing from metal type. Original metal type is cast so that each letterform sits on its own block, or 'body'. When certain combinations of letters are used, (for example 'fi' or 'fl') it is physically impossible to reduce the spacing, or 'kerning', enough so that these combinations appear to have the same kerning as the rest of the type. This is due to the width of the block, or body of the type, that the letterform sits on. If you were to scan your eyes over something letterpress printed from metal type where ligatures had not been used, the spaces between combinations such as 'fi' and 'fl' would appear too large. So the only way to achieve kerning that is visually correct, is to cast these letter combinations into one single block, known as a ligature. This allows the two letterforms to invade or overhang each other's space slightly, since they sit on the same body, and results in visually correct kerning.

I would conclude that traditionally, in letterpress printing, some ligatures such as the 'fi' and 'fl' combinations served the purpose of ensuring visually correct kerning as described above. You would, of course, still be able to read and make sense of text that had been typeset without using ligatures, but it wouldn't be as aesthetically pleasing, and would appear 'gappy'. Fast-forward several centuries to modern type design and the same principals apply. Many faces are still designed to include common ligatures such as the 'fi' and 'fl' combinations, because it simply looks better if these combinations are allowed to encroach on each others' space, when using default kerning. In contrast, you can see from the images at the top of this post that the 'ct' and 'st' combinations don't really need to encroach on each others' space. You could draw a vertical line cleanly between the 'c' and the 't', and likewise the 's' and the 't'. So I think these particular combinations are more likely to be decorative as opposed to functional in terms of visually correct kerning - they wouldn't have needed to have been produced as ligatures. But their presence in type may well date back to their historical use in handwriting, when perhaps joining those combinations of letters together allowed for faster writing, or represented a contraction eg. 'saint' became 'st'. Bearing in mind the fact that before the invention of letterpress printing it took around 3 years to produce a single hand-written copy of the Bible, scribes were undoubtedly looking for short-cuts to speed up that process!

So should you use standard ligatures as default in desktop publishing? I would say yes, because they have been designed to ensure that type reads smoothly without looking 'gappy' when set using default kerning (spacing between letterforms). Discretionary ligatures are more likely to include more decorative letter pairings such as the 'st' and 'ct' pairings at the top of this post. As a graphic designer I might use them as an interesting visual element, for example in a headline on a magazine page where I wanted to make a feature of the type. But I probably wouldn't use them for the body copy on that same page, as, over a long read they could be quite distracting.

Hope that helps answer your question.

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