The verb places the action, state or process within the sentence and is organized by person, number, tense and mood. In Spanish, the regular conjugation starts from a stable stem and endings that mark grammatical information, as in [Regular Verbs]. When the stem changes, the verbal form preserves its function but changes its stem to reflect present, past or lexical irregularity. These alterations appear in various groups and it is useful to distinguish them from the completely irregular forms that are studied in [Irregular Verbs].

Regular verbs preserve the stem and follow a fixed paradigm for each ending. In the present indicative, the model base is o, as, a, amos, áis, an for -ar verbs, with the parallels in -er and -ir. hablar, comer and vivir show how the ending identifies the verbal group without altering the stem.

PersonaPerson.	VerboVerb.	EjemploExample.
yoI.	habloI speak.	Yo hablo con calmaI speak calmly.
túyou.	hablasyou speak.	Tú hablas y escuchasYou talk and listen.
nosotroswe.	hablamoswe speak.	Nosotros hablamos despuésWe speak afterwards.
vosotrosyou all.	habláishabláis.	Vosotros habláis muy rápidoYou all speak very fast.
ellosthey.	hablanthey speak.	Ellos hablan por la tardeThey speak in the afternoon.

Regular -ar verbs form the present with a stable stem and endings shared across the whole paradigm. This pattern allows immediate recognition of person and number, and serves as a base for comparing with later root changes. The same root-plus-ending logic appears in other verb families, though with marks unique to each group.

PersonaPerson.	VerboVerb.	EjemploExample.
yoI.	habloI speak.	Yo hablo despacioI speak slowly.
túyou.	hablasyou speak.	Tú hablas claroYou speak clearly.
élhe.	hablahe/she talks.	Él habla con el grupoHe talks with the group.
nosotroswe.	hablamoswe speak.	Nosotros hablamos en claseWe speak in class.
vosotrosyou all.	habláishabláis.	Vosotros habláis bienYou all speak well.
ellosthey.	hablanthey speak.	Ellos hablan por turnosThey speak by turns.

The -er verbs follow a pattern very close to that of -ar, but with endings of the -er group. The stem remains stable in regular conjugation and the verb form expresses person and number without altering lexical meaning. Comer represents this behavior clearly in the present.

PersonaPerson.	VerboVerb.	EjemploExample.
yoI.	comoeat.	Yo como tempranoI eat early.
túyou.	comesyou eat.	Tú comes fruta frescaYou eat fresh fruit.
élhe.	comeeats.	Él come en casaHe eats at home.
nosotroswe.	comemoswe eat.	Nosotros comemos juntosWe eat together.
vosotrosyou all.	coméisyou all eat.	Vosotros coméis bienYou all eat well.
ellosthey.	comenthey eat.	Ellos comen despuésThey eat afterwards.

The -ir verbs also maintain a stable stem in the regular present, although their own endings distinguish them from -ar and -er. Living (Vivir) shows this paradigm and helps to recognize the base form before studying groups with vowel alternation. In most regular verbs, the key is to identify first the verb ending and then the grammatical person.

PersonaPerson.	VerboVerb.	EjemploExample.
yoI.	vivoI live.	Yo vivo cercaI live nearby.
túyou.	vivesyou live.	Tú vives tranquiloYou live calmly.
élhe.	vivehe/she lives.	Él vive aquíHe lives here.
nosotroswe.	vivimoswe live.	Nosotros vivimos juntosWe live together.
vosotrosyou all.	vivísyou all live.	Vosotros vivís lejosYou all live far away.
ellosthey.	viventhey live.	Ellos viven contentosThey live happily.

In some present indicative verbs, the root vowel changes from e to ie in all forms except nosotros and vosotros. This pattern affects frequent verbs like pensar and cerrar, which alternate the vowel only when the stressed syllable falls on the root. The change does not alter the verb ending and therefore the paradigm remains recognizable.

PersonaPerson.	VerboVerb.	EjemploExample.
yoI.	piensoI think.	Yo pienso mucho antes de hablarI think a lot before speaking.
túyou.	piensasyou think.	Tú piensas rápidoYou think fast.
élhe.	piensahe/she thinks.	Él piensa con cuidadoHe thinks carefully.
nosotroswe.	pensamoswe think.	Nosotros pensamos juntosWe think together.
vosotrosyou all.	pensáisyou all think.	Vosotros pensáis en silencioYou all think in silence.
ellosthey.	piensanthey think.	Ellos piensan distintoThey think differently.

Another group of irregular present forms changes the root vowel from o to ue in the accented forms. Dormir and volver follow this pattern, while nosotros and vosotros keep the original vowel. The alternation appears in the root and not in the endings, so the conjugation remains identifiable.

PersonaPerson.	VerboVerb.	EjemploExample.
yoI.	duermoI sleep.	Yo duermo pocoI sleep little.
túyou.	duermesyou sleep.	Tú duermes tempranoYou sleep early.
élhe.	duermehe/she sleeps.	Él duerme profundamenteHe sleeps deeply.
nosotroswe.	dormimoswe sleep.	Nosotros dormimos fueraWe sleep outside.
vosotrosyou all.	dormísyou all sleep.	Vosotros dormís bienYou all sleep well.
ellosthey.	duermenthey sleep.	Ellos duermen despuésThey sleep afterwards.

In several -ir verbs, the root vowel changes from e to i in the accented present forms. Pedir and servir are common models of this group, which preserves the alternation throughout the conjugation except in nosotros and vosotros. The person and ending structure remains intact, so the change concentrates only in the root.

PersonaPerson.	VerboVerb.	EjemploExample.
yoI.	pidoI ask for.	Yo pido ayudaI ask for help.
túyou.	pidesyou ask for.	Tú pides consejoYou ask for advice.
élhe.	pidehe/she asks for.	Él pide silencioHe asks for silence.
nosotroswe.	pedimoswe ask for.	Nosotros pedimos juntosWe order together.
vosotrosyou all.	pedísyou all ask for.	Vosotros pedís rápidoYou all order quickly.
ellosthey.	pidenthey ask for.	Ellos piden noticiasThey ask for news.

A less frequent group presents the alternation from u to ue in the present. Jugar is the best-known example and shows that vowel modification can affect different vowels depending on the verb. As in other root changes, the alternation does not appear in nosotros or vosotros.

PersonaPerson.	VerboVerb.	EjemploExample.
yoI.	juegoI play.	Yo juego con amigosI play with friends.
túyou.	juegasyou play.	Tú juegas bienYou play well.
élhe.	juegahe/she plays.	Él juega por diversiónHe plays for fun.
nosotroswe.	jugamoswe play.	Nosotros jugamos juntosWe play together.
vosotrosyou all.	jugáisyou all play.	Vosotros jugáis siempreYou all always play.
ellosthey.	jueganthey play.	Ellos juegan por la tardeThey play in the afternoon.

Some verbs have a special form in the first-person singular and keep the rest of the paradigm with their own rules. Tener gives tengo, decir gives digo and conocer gives conozco, with changes concentrated in the yo form. This group also includes many verbs called yo-go and several -cer and -cir verbs, which are studied together with the most frequent irregularities of [Irregular Verbs].

PersonaPerson.	VerboVerb.	EjemploExample.
yoI.	tengoI have.	Yo tengo tiempoI have time.
yoI.	digoI say.	Yo digo la verdadI tell the truth.
yoI.	conozcoconozco.	Yo conozco la ciudadI know the city.
yoI.	hagoI do.	Yo hago la tareaI do the homework.
yoI.	salgoI leave.	Yo salgo ahoraI leave now.

In the preterite of -ir verbs with stem change, the alternation appears only in the third person singular and plural. Pedir yields pidió and pidieron, while dormir yields durmió and durmieron. This restriction makes the preterite more regular than the present in many verbs of this class.

PersonaPerson.	VerboVerb.	EjemploExample.
élhe.	pidióhe asked.	Él pidió comida anocheHe ordered food last night.
ellosthey.	pidieronthey asked.	Ellos pidieron ayuda ayerThey asked for help yesterday.
élhe.	durmióhe slept.	Él durmió prontoHe slept early.
ellosthey.	durmieronthey slept.	Ellos durmieron tardeThey slept late.
élhe.	sirvióhe served.	Él sirvió téHe served tea.
ellosthey.	sirvieronthey served.	Ellos sirvieron a todosThey served everyone.

Non-finite forms do not indicate person and serve as bases for other constructions. The infinitive ends in ar, er or ir; the gerund ends in ando or iendo; and the participle ends in ado or ido. Some participle forms are irregular and must be recognized as learned lexical forms, such as dicho, hecho and escrito.

FormaForm.	TerminaciónEnding.	EjemploExample.
infinitivoInfinitive.	arar.	hablarto speak.
gerundiogerund.	andopresent participle ending -ando.	hablandospeaking.
gerundiogerund.	iendopresent participle ending -iendo.	comiendoeating.
participioParticiple.	adopast participle ending -ado.	habladospoken.
participioParticiple.	idopast participle ending -ido.	vividolived.
participio irregularirregular participle.	especialspecial.	dichosaid.

Periphrases combine an auxiliary verb with a non-finite form to express intention, progression, obligation or recent result. Ir a + infinitive marks near future, estar + gerund expresses development, tener que + infinitive indicates necessity and acabar de + infinitive signals a recently completed action. These structures are very productive and are studied along with [Perífrasis Verbales].

EstructuraStructure.	FunciónFunction.	EjemploExample.
ir a más infinitivogo to + infinitive.	futuro próximonear future.	Voy a estudiar ahoraI am going to study now.
estar más gerundioestar + gerund.	acción en progresoaction in progress.	Estoy leyendo despacioI am reading slowly.
tener que más infinitivohave to + infinitive.	obligaciónObligation.	Tengo que salir prontoI have to leave soon.
acabar de más infinitivohave just + infinitive.	acción recienterecent action.	Acabo de llegar hace un momentoI just arrived a moment ago.

The form of address and the choice of tenses share regional variation in the Spanish-speaking world. In the Río de la Plata, vos modifies several present forms, while in many parts of Spain vosotros is used. There are also differences in the use of the present perfect and the simple past according to region and register.

RegiónRegion.	FormaForm.	Definición regionalRegional definition.	EjemploExample.
Río de la PlataRio de la Plata.	vosyou (vos).	Sustituye a tú y cambia la conjugación verbal.It substitutes for tú and changes the verb conjugation.	Vos pensás distintoYou think differently.
EspañaSpain.	vosotrosyou all.	Se usa como plural de segunda persona en el presente.It is used as the second-person plural in the present.	Vosotros habláis aquíYou all talk here.
AméricaAmerica.	pretérito simplesimple past.	Suele preferirse para acciones pasadas terminadas.It is usually preferred for completed past actions.	Ayer comí tempranoYesterday I ate early.
EspañaSpain.	pretérito perfectopresent perfect.	Suele preferirse para hechos recientes o vinculados al presente.It is typically used for recent events or events related to the present.	Hoy he comido yaToday I have already eaten.

Among irregular and stem-changing verbs, some appear very early in learning because they are common and highly frequent. Tener, decir, conocer, hacer, and salir combine first-person irregularity with highly productive lexical stems, while pensar, dormir, pedir and jugar establish the main patterns of vowel alternation. Recognizing them allows you to interpret and produce complex sentences with less effort and to better understand real-use constructions.