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Ligatures: Benefits and Pitfalls

Accessibility Considerations for Designing with Ligatures in InDesign and Illustrator

9/29/2021 3:35:21 PM

Lowercase letters F i (not touching), arrow pointing to lowercase letters f i with horizontal bar of f touching top of the i.

By Jeremy DePew, Senior Designer at Minnesota IT Services

Anyone who creates documents or uses graphic design software has probably encountered a typographic feature called ligatures. A common feature in OpenType fonts, ligatures are replacement characters for certain letter pairs, such as fi, fl, ff, ffi, ffl, etc. They can improve the appearance of characters that have features that visually collide when used next to each other. In the example above, the letters “f” and “i” display as distinctly separate characters (left), as well as in ligature form (right). 

In the example where the characters are distinctly separate, the dot of the letter “i” awkwardly bumps into the ascender (top) of the letter “f.” In the ligature example:

  • the two letters have joined crossbars,
  • the dot of the “i” is missing, and 
  •  the ascender of the letter “f” travels over the letter “i.” 

You may not consciously think about ligatures as you type, since you can select characters individually and spell checkers don’t flag them as misspellings. However, there are some accessibility considerations that you should think about when you use them as you design documents, graphics, or websites. 

This article will give a high-level overview of problems ligatures can cause, as well as provide some workarounds for solving those issues. These observations and suggestions are for Adobe InDesign and Adobe Illustrator, two common applications used by graphic designers.

Less character separation = less readability for some audiences

When you increase the spacing between characters, many of us can more easily read content. We may be: 

  • in a hurry 
  • reading on a small device 
  • or trying to copy the letters into another application. 

But for some people, the spacing is essential. This includes people that have a disability that impacts reading, such as people with dyslexia and some individuals that have had strokes or brain injuries. Accuracy and speed of reading increases for these people when document authors and designers follow readability best practices. In his article "A Guide to Understanding What Makes a Typeface Accessible,"  Gareth Ford Williams includes:

  • Letters should be easily distinguishable from one another.
  • Ensure the typeface has adequate letter spacing.
  • There should be a visible difference between capital height and ascenders.

Character encoding errors 

When you generate a PDF from InDesign or Illustrator for a document that uses ligatures, and then run an accessibility check on that PDF in Adobe Acrobat Pro, you may run into a “character encoding – failed” error. The Worldwide Web Consortium (W3C) describes character encoding as “a set of mappings between the bytes in the computer and the characters in the character set.” There are many different encoding types. The failure of a glyph (graphical depiction of a character) to map correctly could cause individual font glyphs to be displayed incorrectly or not at all in documents (discussed in PDF/A in a Nutshell - PDF). It could also potentially impact the ability of assistive technology to read or pronounce words correctly, even if they are visually present. For example, I saved a test PDF document from Illustrator containing three different words with ligatures. A JAWS screen reader (version 2021.2107.12) read: 

  • Coee (should have been “coffee,” but ff was a ligature) 
  • t (should have been “fit,” but fi was a ligature) 
  • avor (should have been “flavor,” but fl was a ligature) 

In the testing I performed, PDFs containing ligatures generated from Adobe Illustrator consistently had character encoding errors.

Acrobat accessibility checker flagging a character encoding - failed error in a PDF. Content highlighted is 2 letter fs that visually appear joined together.

Figure 1 - Acrobat accessibility checker flagging a “character encoding – failed” error in a PDF exported from Illustrator.

Older versions of InDesign also caused this error in PDFs, though it wasn’t present in the most recent version of InDesign I tested with, version 16.3 x64.

Acrobat accessibility checker passing character encoding. Content contains letter combinations of 2 ffs, fi, and fl that visually appear joined together.

Figure 2 - Acrobat accessibility checker showing that character encoding passed in a PDF exported from InDesign version 16.3 x64.

If you’re having trouble with ligatures

If you’re having trouble with character encoding issues in PDFs, or want to better support readers who need greater character separation, you can choose to turn the ligatures off. Your characters will then appear as individual letterforms and use the default kerning information (space between individual letters) that is built into the font.

You can easily remove the ligatures from selected text or entire text boxes. You can also define ligature activation through your styles. However, there is no apparent way to globally disable ligatures in Adobe Creative Cloud applications (such as through a setting in Preferences > Type).

How to turn off ligatures in Adobe InDesign

  1. Open the Character panel by going to Window > Type > Character.
  2. Open the panel menu and select Ligatures to activate or deactivate them.
  3. If you turn ligatures off with no text or frame selected, you are turning off ligatures for any subsequent text items you create within this document. Note: ligatures will be enabled by default the next time you create a new document.

Character panel flyout menu showing ligatures menu item with check mark.

Disabling ligatures using InDesign styles

  • You can turn off ligatures in your paragraph and character styles.
  • Find this setting under the "Basic character formats" tab.
New Paragraph Style menu in Adobe InDesign showing Ligatures option checked in Basic Character Formats tab Turn ligatures off in Illustrator.

Turn ligatures off in Illustrator

  1. Access the OpenType panel by going to Window > Type > OpenType. 
  2. On this panel, the first menu item activates Standard Ligatures, while the third button activates Discretionary Ligatures. This article only deals with the more common standard ligatures.
OpenType panel flyout menu in Adobe Illustrator showing check mark next to Standard Ligatures.
Though ligatures are pretty, there are accessibility considerations that a designer or document creator should be aware of with their use. Fortunately, those issues are easily solved through the workarounds described above.


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