Nasal Vowel Sounds
Normally when a vowel or vowel combination is followed by the letters m or n, that vowel is nasalized. When this is the case the letters m or n are not pronounced; they serve only to mark the nasalization.
The letter combinations ain, aim, eim, ein, in, im, ym, yn and ien all have the nasalized vowel sound [ɛ̃].
Nasalized [ɛ̃]
Oral
The letter combination un is pronounced as [œ̃] .
Nasalized
Oral
The letters an, en, and em are pronounced as [ã]
The letters on are pronounced with the nasalized vowel [ɔ̃]
Nasalized
Oral
The letters n or m following a vowel combination don't always signify a nasal sound. When the n or m that follows the vowel is the last letter in a word or if only a single consonant follows the m or n, the vowel is always nasalized.
But if the m or n is followed by a mute e the vowel is not nasalized. The third person verb endings (-ent) are considered a mute e.
If a vowel immediately follows the m or n and that vowel is not a mute e, the m or n is part of the syllable of this vowel and is therefore not nasal.