6.5 Digraphs (Diphthongs) and Trigraphs [V.25, X.34.b(5), XIII.42.c]

In order to preserve proper pronunciation, the letters of a digraph or a trigraph must not be separated.

A DIGRAPH is any two adjoining letters that combine to make one sound, e.g., the ph in graphic.

A DIPHTHONG is a digraph composed of two adjoining vowels that make one sound, e.g., the oi in coil.

A TRIGRAPH is three letters combining to make one sound, e.g., the eau in bureau.

Because the ae in aerial and the oe in Goering are diphthongs and cannot be separated, the er contraction cannot be used; nor can the sign for ed be used in Oedipus, encyclopaedia, or aedile. Ble cannot be contracted in tableau because to do so would separate the letters of the trigraph eau.

There is an exception to this rule. When common suffixes such as er and ed are added to base words ending in a vowel, which sometimes creates a digraph or trigraph, the er and ed contractions are used. Examples:










Note that not all adjoining vowels are diphthongs. For example, in the words coeducate and coerce the ed and er contractions are used because the oe does not combine to form a diphthong (one sound)—and all of the letters of the contraction fall into the same syllable.

• Note: The diphthongs ae and oe are sometimes printed together (ζ, oe). In braille they are transcribed as separate letters. Use a transcriber's note (to be studied later) to explain this change.