Note 38 — VOWEL-LIGATURES[38] (Æ AND Œ)
Reading edition
The separately written oe, ae are ‘digraphs’, because the sounds they represent are in modern pronunciation not diphthongs, though they were such in classical Latin; but ch, ph, sh are also digraphs. Æ, æ, Œ, œ, are rather single letters than digraphs, though they might be called ligatured digraphs.—H. B.