The transformation of an oral open front unrounded vowel /a/ into its nasalized counterpart /ã/ is a common and natural phonetic process observed across many languages. This shift, known as vowel nasalization, typically occurs when an oral vowel is in proximity to a nasal consonant (like /m/ or /n/). The velum, or soft palate, lowers, allowing air to escape through both the mouth and the nose simultaneously, resulting in the characteristic nasal quality of the vowel. Over time, this contextual nasalization can become a distinctive feature of the language, leading to phonemic nasal vowels where the presence or absence of nasalization can differentiate word meanings.
aldeão→aldeã— In Portuguese, the masculine noun 'aldeão' (countryman) forms its feminine 'aldeã' (countrywoman) with a shift from an oral vowel (often realized as a nasal diphthong in the masculine, but the underlying oral vowel is nasalized in the feminine form) to the nasalized open front unrounded vowel /ã/.
/maw/→/mɐ̃w̃/— The word 'mau' (bad) contrasts with 'mão' (hand), where the vowel in 'mão' is a nasalized diphthong, demonstrating the phonemic contrast of nasalization involving a low vowel.
VN (oral vowel + nasal consonant)→ṼN (nasalized vowel + nasal consonant)— In the Old French period, vowels became nasalized under regressive assimilation when followed by a nasal consonant. This process, where an oral vowel followed by a nasal consonant (VN) became a nasalized vowel followed by a nasal consonant (ṼN), was a crucial step in the development of phonemic nasal vowels in Modern French.
/haː/→[hãː]— Thai exhibits predictable vowel nasalization of low vowels, such as /a/, after word-initial /h/. For instance, /haː/ 'five' becomes [hãː].
