Irregular verbs maintain the central function of the verb in the sentence, but deviate from regular patterns to mark tense, person or verbal form. In Portuguese, irregularity can affect the stem, the thematic vowel, the endings or even the participle, and for that reason it is important to recognize the base model before memorizing the exceptions. The regular reference forms help to perceive the contrast with Regular Verbs, especially in the conjugations in -ar, -er and -ir.

Ser and ir are totally irregular verbs and must be learned by their own forms, because they do not follow a productive paradigm. The most frequent basic forms appear early in communication and also serve as support for other grammatical constructions. In real usage, these forms often appear in simple tenses and in periphrases with auxiliary verbs.

PessoaPerson	VerboVerb	ExemploExample
EuI	souI am	Eu sou estudante, e tu és colega.I am a student, and you are a colleague.
TuYou	ésyou are	Tu és pontual, e ela é paciente.You are punctual, and she is patient.
EleHe	éis	Ele é médico, e nós somos vizinhos.He is a doctor, and we are neighbors.
EuI	vouI go	Eu vou cedo, e depois volto.I go early, and then I’ll be back.
TuYou	vaisyou go	Tu vais à escola, e ele fica em casa.You go to school, and he stays at home.
EleHe	vaihe goes	Ele vai ao mercado, e nós seguimos amanhã.He goes to the market, and we set out tomorrow.

Estar and haver also belong to the totally irregular group, but they perform very different functions. Estar expresses state, location and part of progressive periphrases, while haver appears in existential uses and as an auxiliary in compound tenses. The inflected form of haver is essential to recognize formal and archaic constructions, in addition to appearing in fixed phrases.

PessoaPerson	VerboVerb	ExemploExample
EuI	estouI am	Eu estou em casa, e ela está no trabalho.I am at home, and she is at work.
TuYou	estásyou are	Tu estás aqui, e nós estamos perto.You are here, and we are nearby.
EleHe	estáis	Ele está feliz, e a turma está calma.He is happy, and the class is calm.
Terceira pessoaThird Person	háthere is	Há tempo, e tudo muda com calma.There is time, and everything changes calmly.
PassadoPast	houveThere was	Houve reunião, e depois todos saíram.There was a meeting, and afterwards everyone left.
Forma pluralPlural Form	hãothere will be	Hão poucos casos, e o uso é literário.There are few cases, and the usage is literary.

Some verbs retain the regular paradigm but alter the root vowel in specific forms. This vowel alternation occurs especially in the present indicative and in other contexts where the word’s stress requires an internal change. Verbs such as pedir, sentir and dormir show that irregularity can be predictable by the verbal person.

PessoaPerson	VerboVerb	ExemploExample
EuI	peçoI ask for	Eu peço ajuda, e tu pedes silêncio.I ask for help, and you ask for silence.
TuYou	pedesyou ask	Tu pedes calma, e ele responde depressa.You ask for calm, and he answers quickly.
EleHe	pedeyou ask	Ele pede um livro, e nós oferecemos outro.He asks for a book, and we offer another.
EuI	sintoI feel	Eu sinto frio, e ela sente sono.I feel cold, and she feels sleepy.
TuYou	sentesyou feel	Tu sentes o vento, e eles sentem paz.You feel the wind, and they feel peace.
EleHe	dormehe sleeps	Ele dorme cedo, e nós dormimos tarde.He sleeps early, and we sleep late.

Some irregularities are orthographic and serve to keep the correct sound of the verb form. In these cases, pronunciation does not change in a relevant way, but the spelling adapts the consonant or the vowel to preserve readability. Começar and pagar are frequent examples, and the same principle appears in various forms of the pretérito perfeito.

IdeiaIdea	ExemploExample
A letra c mantém o som duro antes de e.The letter c keeps the hard sound before e.	Eu comecei cedo, e ele começou depois.I started early, and he started later.
A letra g mantém o som de j antes de e.The letter g keeps the j-sound before e.	Eu paguei a conta, e ela pagou no dia seguinte.I paid the bill, and she paid the next day.
A escrita adapta-se para conservar a pronúncia.The spelling adapts to preserve pronunciation.	Nós chegámos cedo, e eles chegaram mais tarde.We arrived early, and they arrived later.

Some verbs present a special first-person form in the present indicative, while the rest of the paradigm remains more regular. Pôr, saber and ver are central examples because the change appears in the most-used form of each verb. This irregularity helps to recognize forms such as ponho, sei and vejo in texts and conversations.

PessoaPerson	VerboVerb	ExemploExample
EuI	ponhoI put	Eu ponho a mesa, e tu pões os copos.I set the table, and you set the glasses.
EuI	seiI know	Eu sei a resposta, e ele sabe o caminho.I know the answer, and he knows the way.
EuI	vejoI see	Eu vejo a praia, e nós vemos o mar.I see the beach, and we see the sea.

The regular -ar paradigm functions as a reference model to compare simple forms and recognize irregular deviations. Amar shows the typical sequence of endings and helps identify where other forms diverge from the pattern. From this base, it becomes easier to distinguish real irregularity from simple orthographic variation.

PessoaPerson	VerboVerb	ExemploExample
EuI	amoI love	Eu amo o inverno, e tu amas o verão.I love winter, and you love summer.
TuYou	amasyou love	Tu amas música, e ela ama poesia.You love music, and she loves poetry.
EleHe	amahe loves	Ele ama o campo, e nós amamos a cidade.He loves the countryside, and we love the city.
TuYou	amasteyou loved	Tu amaste o livro, e eles amaram a história.You loved the book, and they loved the story.
EleHe	amouhe loved	Ele amou a carta, e o grupo aprovou a ideia.He loved the letter, and the group approved the idea.

The -er paradigm shows the regular structure that serves as a comparison for verbs like comer. The regular forms help to perceive the alternation between root and endings, especially when the verb does not display internal change. This model is useful for understanding simple tenses and also for recognizing regular participles linked to the base verb.

PessoaPerson	VerboVerb	ExemploExample
EuI	comoI eat	Eu como fruta, e tu comes sopa.I eat fruit, and you eat soup.
TuYou	comesyou eat	Tu comes cedo, e ele come mais tarde.You eat early, and he eats later.
EleHe	comehe eats	Ele come pão, e nós comemos queijo.He eats bread, and we eat cheese.
TuYou	comesteyou ate	Tu comeste bem, e eles comeram pouco.You ate well, and they ate little.
EleHe	comeuhe ate	Ele comeu tudo, e a família ficou satisfeita.He ate everything, and the family was satisfied.

The paradigm in ir is another regular reference model, although some verbs in this class show internal changes in other tenses. Partir shows the typical organization of regular forms and makes it easy to compare the alternations of more complex verbs. This pattern is very important for understanding the relation between root, ending and non-finite form.

PessoaPerson	VerboVerb	ExemploExample
EuI	partoI leave	Eu parto cedo, e tu partes depois.I depart early, and you depart later.
TuYou	partesyou leave	Tu partes amanhã, e ele parte agora.You leave tomorrow, and he leaves now.
EleHe	partehe leaves	Ele parte de Lisboa, e nós partimos de Porto.He leaves from Lisbon, and we leave from Porto.
TuYou	partisteyou left	Tu partiste ontem, e eles partiram antes.You left yesterday, and they left earlier.
EleHe	partiuhe left	Ele partiu tranquilo, e a viagem continuou.He left calmly, and the trip continued.

Non-finite forms do not mark person and are essential for building periphrases and compound tenses. The infinitive ends in -ar, -er or -ir, the gerund in -ando, -endo or -indo, and the participle usually ends in -ado or -ido. There are, however, irregular participles that require special attention, especially in constructions with auxiliary verbs.

FormaForm	VerboVerb	ExemploExample
InfinitivoInfinitive	amarto love	Querer amar, e depois aprender.Wanting to love, and then learning.
GerúndioGerund	amandoloving	Estar amando, e continuar feliz.Being in love, and continuing to be happy.
ParticípioParticiple	amadoloved	Ter amado, e guardar a memória.Having loved, and keeping the memory.
InfinitivoInfinitive	comerto eat	Desejar comer, e preparar a mesa.Wanting to eat, and to set the table.
GerúndioGerund	comendoeating	Estar comendo, e falar depois.Eating, and speaking later.
ParticípioParticiple	comidoeaten	Ter comido, e sentir se bem.Having eaten, and feeling well.
InfinitivoInfinitive	partirto leave	Decidir partir, e voltar amanhã.Deciding to leave, and returning tomorrow.
GerúndioGerund	partindoleaving	Estar partindo, e olhar para trás.To be leaving, and looking back.
ParticípioParticiple	partidoleft	Ter partido, e seguir em frente.Having left, and moving forward.

Several frequent verbs have irregular participles that coexist with the regular participle or replace it in specific uses. Fazer, dizer, ver and pôr show very stable forms in standard Portuguese, especially in compound tenses and in passive constructions. The choice of participle often depends on the auxiliary and the variety of language used.

VerboVerb	ParticípioParticiple	ExemploExample
fazerto do	feitodone	Ter feito o trabalho, e descansar depois.Having done the work, and rest afterwards.
dizerto say	ditosaid	Ter dito a verdade, e seguir em paz.Having told the truth, and moving on in peace.
verto see	vistoseen	Ter visto o filme, e contar a história.Having seen the film, and tell the story.
pôrto put	postoplaced	Ter posto a mesa, e chamar os convidados.Having set the table, and calling the guests.

Periphrases combine an auxiliary verb with a non-finite form to express ongoing action, intention, necessity or conclusion. In Portugal, it is very common to use estar a + infinitive for actions in progress, while in Brazil the gerund is preferred in the same function. It is also common to have ir + infinitive, acabar de + infinitive and ter de + infinitive, which organize the temporal and modal meaning of the sentence.

IdeiaIdea	ExemploExample
Ir mais infinitivo exprime futuro próximo ou intenção.Ir + infinitivo expresses near future or intention.	Vou estudar, e depois descanso.I will study, and then rest.
Estar a mais infinitivo exprime ação em curso em Portugal.Estar a + infinitivo expresses action in progress in Portugal.	Estou a ler, e não quero interrupções.I am reading, and I don’t want interruptions.
Estar mais gerúndio exprime ação em curso no Brasil.Estar + gerúndio expresses action in progress in Brazil.	Estou lendo, e a música continua baixa.I am reading, and the music keeps playing softly.
Acabar de mais infinitivo exprime conclusão recente.Acabar de + infinitivo expresses a recent completion.	Acabei de chegar, e já procuro lugar.I’ve just arrived, and I’m already looking for a place.
Ter de mais infinitivo exprime obrigação.Having to + infinitive expresses obligation.	Tenho de sair, e volto mais tarde.I have to leave, and I’ll be back later.

Irregular verbs show that Portuguese conjugation combines predictable patterns with historically and phonetically very stable changes. Ser, ir, estar and haver require direct memorization, while pedir, sentir and dormir reveal root changes that are more systematic. Mastery of non-finite forms, irregular participles and periphrases with auxiliary verbs prepares the reading of simple tenses, compound tenses and structures that appear early in Present Indicative, Compound Tenses and Subjunctive Mood.