The Trema and the Apostrophe

Dutch uses two small marks that English speakers tend to treat as optional decoration and then get wrong: the trema (the two dots, ë ï ö ü — also called the diaeresis) and the apostrophe. Neither is decorative. The trema is a piece of syllable grammar: it tells the reader where one syllable ends and the next begins, changing how the word is read aloud. The apostrophe is part of Dutch plural and genitive morphology: leaving it out (or adding it the English way) produces a misspelling and sometimes a misreading. This page covers both. The acute and grave accents of emphasis and loanwords (café, één, scène) are a separate topic — see accent marks.

The trema: breaking up a false digraph

Dutch has many vowel digraphs — two letters read as one sound: aa, ee, oo, uu, ie, oe, eu, ij, ei, au, ou. The reader's default is to swallow adjacent vowels into one of these. The trema exists to block that default when the two vowels actually belong to separate syllables. The two dots say: "read me on my own — start a new syllable here."

Compare what would happen without it:

So the trema is genuinely grammatical: ruïne and a hypothetical ruine would be syllabified — and pronounced — differently. This is the key insight English speakers miss. In English a diaeresis (as in the old spelling coöperate) is a quaint typographical flourish; in Dutch it is load-bearing.

The everyday trema words

Two patterns generate most tremas:

• The -ën plural on a word already ending in a vowel-letter that would clash: knie → knieën, zee → zeeën, idee → ideeën, industrie → industrieën. Without the dots, ee
  • en would read as one long ee.
• The -iën / -ën noun and country endings: financiën, België, bacteriën, provincie → provinciën.

The 2006 reform: trema vs hyphen in compounds

There is one nuance worth knowing. The trema is used inside a single word stem. But when the vowel clash happens at the seam of a compound (two whole words joined), the modern rule (since the 2006 spelling reform) uses a hyphen, not a trema. So:

• Within a stem: coördinatie, reünie → trema.
• At a compound seam: zee + eend → zee-eend (a duck species), na + apen → na-apen (to mimic), auto + ongeluk → auto-ongeluk (car accident) → hyphen.

The logic: the trema lives inside one word; once you cross a word boundary, the hyphen marks the join instead. (Older texts you'll still see use zeeëend; the modern standard is zee-eend.)

The apostrophe: plurals, genitives, and abbreviations

The Dutch apostrophe does three specific jobs. It is not an all-purpose plural marker the way English speakers fear — it appears only in these cases.

1. Plural of words ending in a single stressed vowel-letter

When a word ends in a, o, u, i, y (a single vowel letter carrying length), the plural is 's — the apostrophe keeps that vowel long, since a bare -s might invite a short reading.

Common members: foto's, auto's, baby's, oma's, opa's, menu's, taxi's, paraplu's, ski's, hobby's, sms'je (the diminutive of an abbreviation also takes the apostrophe). Words ending in a consonant or in a vowel digraph do not take it: tafels, huizen, ideeën.

2. The genitive of names ending in a sibilant or long vowel

To show possession ("Anna's car"), Dutch adds 's to a name that ends in a long vowel or a vowel-letter — exactly the same apostrophe-plus-s as English, here:

But a name already ending in an s, x, z (a sibilant) takes only a bare apostrophe — no second s — because the s sound is already there:

3. The set phrases with 's (a frozen old genitive)

A handful of fixed expressions begin with 's — a shrunken remnant of the old genitive article des ("of the"). You can't generate these; you learn them:

• 's morgens, 's middags, 's avonds, 's nachts — "in the morning / afternoon / evening / at night".
• 's-Gravenhage — the formal name of The Hague (literally "the count's hedge/grove"); also 's-Hertogenbosch.
• 's zomers, 's winters — "in summer / in winter" (a slightly old-fashioned register).

Note the capitalisation quirk in 's-Gravenhage: the 's stays lowercase and the next letter is the capital (G). At the start of a sentence, 's morgens likewise keeps the 's lowercase and capitalises the following word ('s Morgens...).

Common Mistakes

Key Takeaways

• The trema (ë ï ö ü) breaks two vowels into separate syllables, blocking a false digraph: coördinatie, reünie, ruïne, geïnteresseerd, financiën, België, drieëntwintig. It is grammatical, not decorative.
• The -ën plural (knieën, ideeën) and country/noun endings (België, financiën) are the main trema generators.
• Since 2006, a vowel clash at a compound seam uses a hyphen, not a trema: zee-eend, na-apen, auto-ongeluk.
• The apostrophe forms the plural of single-vowel words (foto's, baby's, oma's) and the genitive of names (Anna's auto; bare apostrophe after a sibilant: Hans').
• Never put an apostrophe on an ordinary plural (tafels, not tafel's).
• Fixed 's phrases ('s morgens, 's-Gravenhage) are a frozen old genitive — memorise them.