Disclaimer: (1) this is an oversimplification, (2) I’ve zero formal training in phonology, (3) I’m only familiar with Hollandic Dutch.

Just like other West Germanic languages, vowel length is important in Dutch. They are often referred to as “long” and “short” vowels, but more accurately they can be described as “tense” and “lax” vowel since not only duration but also articulation is different between some pairs.

The way I learnt them was to look as them in two big groups according too their ortography: monophthongs and diphthongs. Notice this distinction is only ortographic, and not really phonetic.

Orthographic monophthongs and consonant duplication

Dutch orthographic monophthongs are:

  • ⟨a⟩ tense /aː/ and lax /ɑ/,
  • ⟨e⟩ tense /eː/ and lax /ɛ/,
  • ⟨i⟩ lax /ɪ/,
  • ⟨o⟩ tense /oː/ and lax /ɔ/,
  • ⟨u⟩ tense /yː/ and lax /ʏ/.

Here are two diagrams that show the rough positions, note that the tense vowels are written as double vowels. Also note that: some orthographic monophthongs are actually phonetic up-glides.

Rough position of tense and lax orthographic monophthongs, as written:

Rough position of tense and lax orthographic monophthongs, as written

Rough positions of tense and lax orthographic monophthongs, as pronounced:

Rough positions of tense and lax orthographic monophthongs, as pronounced

Disclaimer: the “lax e” from this text can be realised as a mid-open front vowel /ɛ/, or a schwa /ə/. IMHO, this distinction is not that important.

The tricky part of writing these vowels, however, is to understand when to double them in orthography and when not. First we need to understand what “open” and “closed” syllables are:

Open syllables have no coda, or no consonant at the end, as in “hi”. Closed syllables have a coda, or a consonant at the end, as in “hit”.

Follow the following rules, in order, to figure out how to pronounce an (orthographic) monophthongs:

  • In the last (or only) syllable of a word, ⟨e⟩ is lax and ⟨ee⟩ is tense (regardless if the syllable is open or closed).
  • In an open syllable ⟨e⟩ is ambiguous, sorry! You’ll get the hang of it.
  • In an open syllable, all other vowels are tense.
  • In a closed syllable, single vowels are lax, and double vowels are tense.

Now some examples:

  • mee (along) has a tense e, but de (the) has a lax e.
  • leren (to learn) first has a tense e, then a lax e; but luisteren (to listen) has two lax e’s.
  • ga (I go), has a tense a; the u in menu is tense.
  • kom (I come) has a lax o; but loop (I walk) has a tense o.

An implicit rule of Dutch is that vowel tenseness does usually not change when a word inflects. And when it does, it can be considered an exception.

For example: when a verb is conjugated, a noun is pluralised, or an adjective agrees.

This implies that, to preserve the tenseness of a vowel in spelling, both vowels and consonants may be written single or double at the word boundary.

An example of variable vowel spelling: gaan (to go) is a tense-vowel stem. But the conjugation for “I go” drops the -n ending. That becomes ik ga ✓ and not ik gaa ✗.

An example of a variable consonant spelling: slak (snail) is a lax-vowel stem. But slakken ✓ (snails) is written with a double k so that the stem is kept “closed”. Slaken ✗ would be wrong and pronounced differently, although it is a valid word but has a different meaning.

But note: unlike in Italian or Japanese, there are no long consonants (gemination) in Dutch.

Orthographic diphthongs

Dutch (orthographic) diphthongs are always the nuclei of long syllables.

They are:

  • ⟨au⟩ /ɑu̯/
  • ⟨ei⟩ /ɛi̯/
  • ⟨ie⟩ /iː/
  • ⟨ij⟩ /ɛi̯/
  • ⟨oe⟩ /uː/
  • ⟨ou⟩ /ɑu̯/

Rough positions of orthographic diphthongs:

Rough positions of orthographic diphthongs

⚠️ Notice that some orthographic diphthongs are actually phonetic monophthongs.

Also, they are easy to spell since they are always long syllables. Hence there are never double consonants after orthographic diphthongs.
Exceptions

There are more exceptions not covered here, such as, when compounding words, we don’t need to alter the individual parts’ orthography. But that is easy or uncommon enough to learn hereafter, so they’re not covered in this text.
Funny IJ pet-peeves

This is my pet-peeves of Dutch orthography. Almost everything else is so well designed except this digraph.

Remembering the rules above, except with e as a nucleus, open syllables are always long and spelt with a single “pure” vowel, or with a diphthong—which is necessarily two different letters.

But ⟨ij⟩ should be capitalised together as in the river IJ that runs along Amsterdam. This is likely due to it developing out of a long ⟨i⟩, that was alternatively spelt ⟨ii⟩ or ⟨ie⟩ or ⟨y⟩ until standardisation. And because it comes from a formerly single letter, it may be inconsistently treated as single or double letter for capitalisation, stylisation, encoding, collation, education purposes.

Ridiculous.