The Dutch trema (¨): geïnteresseerd, ideeën, België

The trema (in Dutch, het trema) is the pair of dots you sometimes see over a vowel: geïnteresseerd (interested), ideeën (ideas). It tells you that two vowel letters standing next to each other belong to different syllables and must be read as two separate sounds, not glued into one.

Put a trema on the second of two vowel letters when that letter opens a new syllable and the pair would otherwise be read as a single sound. Dutch has many two-letter vowel combinations — ee, ie, oe, ei, ui, oo — that normally spell one sound, so without the dots the reader would run the letters together.

1. Spot a spot where two vowel letters meet but belong to different syllables: idee + -en → the two e's of idee and the e of the ending would look like one long ee.
2. Mark the vowel that starts the new syllable with a trema: ideeën (i-dee-en). The dots fall on the third e, the one that opens the last syllable.
3. The trema always sits on the second vowel of the clash, never the first: coördinatie (not cöordinatie), reünie, geïnteresseerd.

The trema is not an accent: it says nothing about stress and never changes which syllable is emphasised. That job belongs to the accent marks.

Compound numbers built on twee, drie and so on keep the trema where the vowels clash.

• tweeëntwintig (twenty-two) — the ë separates the ee of twee from the en join.
• drieëndertig (thirty-three), drieënveertig (forty-three): same pattern after drie.

When the vowel clash happens at the seam where two whole words are glued into a compound, the spelling reform of 1996 replaced the old trema with a hyphen. A trema stays inside a single word; a hyphen marks the join between two words.

• zee (sea) + egel (hedgehog) → zee-egel (sea urchin), with a hyphen.
• na-apen (to mimic), auto-ongeluk (car accident), toe-eigenen (to appropriate): all compounds, all hyphenated.
• Compare zeeën (seas): here -en is only a plural ending, not a second word, so it keeps the trema.

The most common slip is leaving the dots off entirely, because English does not use them. Without the trema, geinteresseerd invites the reader to say ei as one sound (as in trein), and ideeen gives no clue where to break the string of e's. Do not add a trema where the vowels are meant to stay together, though. Some words simply spell the vowel pair as a single sound, so no dots are needed: financieel (financial), politie (police). And a small set of Latin and French endings — -eum, -eus, -ei, -ien — is exempt from the trema rule, so museum (mu-se-um) takes no dots even though its e and u fall in separate syllables.