Broad and Slender Vowels: Caol le Caol agus Leathan le Leathan

Irish has a spelling rule so important that it has its own slogan: caol le caol agus leathan le leathan — "slender with slender and broad with broad".

The two types of vowels

Type	Irish name	Vowels
Broad	leathan	a, o, u (and á, ó, ú)
Slender	caol	e, i (and é, í)

The rule

A consonant (or group of consonants) sitting between two vowels must have vowels of the same type on both sides. If the vowel before is slender, the vowel after must be slender too. If it's broad, the next one must be broad.

This is why you see extra vowels in Irish words, added only to keep the pattern.

Examples with plurals and cases

When a word changes form, a vowel is often added:

Singular	Plural or changed form	Meaning
bád	báid	boat / boats
fear	fir	man / men
leabhar	leabhair	book / books
cat	cait	cat / cats
bord	boird	table / tables

In báid, an i is added before the final d so that the consonant is slender.

How it affects pronunciation

The type of vowel changes how the neighbouring consonant sounds:

• Broad consonants are pronounced with the back of the tongue raised, giving a deeper sound.
• Slender consonants have a lighter, "y"-like glide.

So the d in bád and the d in báid sound different, even though the letter is the same.

Why learners find this useful

1. Spelling: the rule explains many "extra" vowels.
2. Pronunciation: you can read unfamiliar words more accurately.
3. Grammar: endings change to keep the pattern.

Practice

Which vowels are broad and which are slender in these words?

• bean (woman) — e, then a
• doras (door) — o, then a
• cistin (kitchen) — i, i

Tips

1. Memorise the two groups: a, o, u are broad; e, i are slender.
2. When you meet a new form, check whether the rule explains it.
3. Use the dictionary to look up plural forms.

Look up any word with English Irish Dictionary →