Monophthong shows that a vowel is spoken with exactly one tone and one mouth position. For example, when you say "teeth", then while you are creating the sound of the "ee", nothing changes for that sound. A monophthong

ʌ and i – divided into two syllables by the consonant sound n. So we can say that ‘funny’ contains two monophthongs: ʌ and i.





Now say the word ‘guy’. Here we have the same two vowel sounds but this time they are stuck together in one syllable, without any consonant dividing them. So we can say that ‘guy’ contains one diphthong: ʌi. To put it simply: a monophthong is a single vowel and a diphthong is a double vowel.





A monophthong is where there is one vowel sound in a syllable, and a diphthong is where there are two vowel sounds in a syllable.





Let’s look at another example: the word ‘behind’. Here we have three vowel sounds: ə, ʌ and i. The ə is on its own, separated from the other two vowel sounds by the consonant sound h. However the ʌ and i are stuck together to make a double vowel, ʌi, which is the same diphthong in the word ‘guy’. So the word ‘behind’ has three basic vowel sounds divided into two syllables, the first of which contains a monophthong, ə, and the second of which contains a diphthong, ʌi: bəhʌind.





In English we also have a couple of triple vowels called triphthongs, such as in the word ‘fire’, which has three vowels ʌ, ɪ and ə stuck together in one syllable: fʌɪə.

Long and short monophthongs

This section gives an overview of the reasons for distinguishing short and long vowels. These are

1. 
   that phonetic measurements show a difference in duration and frequency values, and
   
2. 
   that there are pairs of words with a different meaning which only differ as to the length of their vowels.
   

Since Frisian has short and long monophthongs, the dimension of vowel length must be accounted for (see Odden (2011) on this dimension in general). There need not be a one-to-one relation between the phonological length of a vowel and its actual phonetic duration. The latter is highly variable, dependent as it is on parameters such as speech rate and speech style. Be that as it may, phonetic measurements — see Graaf (1985) — reveal that an average the short monophthongs have a duration of 116 milliseconds, whereas this is 250 milliseconds for the long ones: the latter have a mean duration which is more than twice as long as that of the former. The short monophthongs are also realized with lower frequency values for both the first and second formant, which implies that they occupy a more central position in the vowel space.

The above is a first reason for distinguishing short from long vowels. But there is also a compelling, purely phonological, reason to do so. There are pairs of words with a different meaning which only differ in vowel length; this means that the vocalic length differences are exploited to create phonological oppositions or, put differently, that they figure in lexical contrasts. Contrasting morpheme pairs for each vowel pair are listed below:

Table 1