Common 2-letter combinations

Digraphs are 2-letter combinations found in words inherited from classical Latin and Greek. In some cases, the digraphs have been replaced by a single letter in modern English writing; in others their spellings are variable.

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Australians vary in their use of the digraph ae. We tend to make it just e when it occurs in the middle of a multisyllable word, but usually keep ae at the beginning of a word or in the first syllable:

encyclopedia     leukemia     medieval
aesthetic     aetiology     faeces     haematology

The ae digraph that marks the plural form of Latin nouns ending in -a (eg larvae, pupae) is usually retained in scientific writing. Other kinds of Latin nouns (eg formula, persona) usually take English plurals (formulas, personas).

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Australians vary in their use of the digraph oe. We use it regularly at the beginning of a word, but less consistently in the middle of a multisyllable word, where it may be reduced to a single vowel:

oedema     oestrogen     oestrus
amoeba     diarrhoea     homeostasis
Did you know? The spelling foetus is probably based on false analogy with Greek-derived words such as oedema and oestrogen. Fetus (which is a Latin word) is preferred in the medical literature, including in Australian medical journals and fetal medicine organisations; see Embryology and ‘Foetus’ or ‘fetus’ – which should it be?
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Different words use ph or f, depending on the word origin. English words with a Greek origin tend to use ph; others use f:

catastrophe     graph     professor     serif

In a few cases, the word can be spelled either way. This is most familiar in the choice between sulphur and sulfur, where sulfur is mandated as the scientific spelling by the International Union of Pure and Applied Chemistry (see Spelling in chemistry). Sulphur remains in the names of fauna (eg sulphur-crested cockatoo) and in literary usage as sulphurous.

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