Portuguese uses oral vowels, nasal vowels, and consonants organized into a relatively stable inventory. Each vowel can change quality depending on the region and tonic stress, but remains as a unit of the system. Consonants are distributed by position in the syllable and can form clusters with predictable rules. Writing represents sounds partially, with much regularity in stressed vowels and in stable consonants.

The basic system has five oral vowels: a, e, i, o, u. These vowels can sound more open or closed without ceasing to be recognizable as the same letter. In stressed syllables, the distinction between open e and closed e, and between open o and closed o, becomes phonemic in many varieties. In unstressed syllables, vowels tend to centralize or reduce, especially e and o.

Nasal vowels are produced by letting air pass through the nose and mouth at the same time. In Portuguese, nasalization is marked in writing by til and by a nasal consonant at the end of a syllable. The perception of nasality depends on duration and context, especially in short words. Nasality can create contrasts in meaning with oral vowels.

Some consonants maintain stable pronunciation in most contexts of Portuguese. P, b, t, d, k, g are plosives and are realized in a way close to the written form. F, v, s, z are fricatives and are distinguished mainly by voicing. M and N are nasal and function as full consonants at the start of a syllable. L and R at the start of a syllable are also predictable.

Some consonants change realization depending on position in the word and the variety of Portuguese. S and z vary strongly at the end of syllables. R varies in word-initial position, between vowels and at the end of syllables. D and t before i or palatal sounds can undergo palatalization in some regions. These variations are systematic and do not prevent understanding among speakers.

Portuguese organizes words into syllables with a preference for simple structure: a consonant followed by a vowel. Tonicity is the primary force of a syllable in the word and determines much of vowel quality. In oxytone words, the last syllable is stressed; in paroxytone words, the penultimate; in proparoxytone words, the antepenultimate. The writing uses diacritics to mark tonic stress when there is a risk of ambiguity.

Vowels in unstressed syllables tend to reduce, especially e and o. In Brazilian Portuguese, the unstressed e can approach /ɪ/ or a central sound. The unstressed o can approach /u/ or a central sound, depending on the context. This reduction facilitates the rhythm of speech without completely erasing the vowel. In many words, reduction coexists with enough preservation to distinguish words.

Consonant clusters like pr, tr, cl, fl are stable and learned as blocks. Clusters with s or x in the middle of the word can cause voice and duration adaptations. At the end of a syllable, a consonant tends to weaken or lean on the following vowel in fast speech. Portuguese avoids long consonant clusters within the same syllable. Syllabic division favors CV and CVC structures with predictable rules.

The letter-sound correspondence is strong for stable consonants and for stressed vowels in regular contexts. C and G change sound according to the following vowel, forming a central reading pattern. X can correspond to several different sounds depending on word history, not by a general phonetic rule. Nh and lh represent palatal sounds characteristic of Portuguese. Efficient reading uses syllable predictability and stress to adjust pronunciation.

Mastering the sounds of Portuguese involves recognizing oral and nasal vowels, identifying stable consonants, and noticing predictable variations like s and r. Tonicity guides vowel quality and the clarity of the syllable in speech. Vowel reduction in unstressed syllables is a central feature of the rhythm of Portuguese. Writing provides regular cues, but auditory perception completes the system in everyday communication.