Vowels of 'rhythm'

It is sometimes said that rhythm is the longest word in English without a vowel. This is an error. Although primary school children are taught that there are five vowels ('A', 'E', 'I', 'O' and 'U'), this is an over-simplification appropriate to people beginning to learn to write. The full picture is more complex. The term vowel is a term of phonetics rather than writing. In fact, the full phonetic nature of rhythm may give rise to dispute among experts; but as it usually pronounced by native English speakers, it may be said to have two vowels.

1. The letter 'Y' is best thought of (by those who have passed the primary stage) as a semivowel. It usually acts as a consonant, but sometimes it performs the function of a vowel.
2. Beginners in phonetics do not always realise that certain sonorant consonants (e.g. '-m-', '-n-', '-l-' and '-r-') can be syllabic: that is, in some contexts, to realise them requires a vowel-like breathing, or continuation. 'Bottle' and the slang 'pudd'n' are examples, as is the last syllables of the names of the Mexican mountain 'Popacatapetl', and a Mexican salamander, the 'axolotl'.

So rhythm can be said to have two vowels.