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Spanish irregular verbs: what are they?

In Spanish, verbs are considered irregular if the stem is modified in one or more persons, in any or all tenses.

However, the ending remains unchanged. Irregular verbs can be classified into three categories:

• diphthong verbs;
• weakening verbs;
• alternating verbs.

Diphthong verbs

The diphthong is a modification of the verb stem. It applies a modification of the vowels when the final “-e” or “-o” of the verb root carries the tonic accent.

It applies to the three persons of the singular (“yo”; “tú”; “él”, “ella”, “usted”) as well as to the third person of the plural (“ellos”, “ellas”, “ustedes”), in the present tense (indicative, subjunctive and imperative).

There are three types of diphthongs:

• the final “-e” becomes “-ie” ;
• the final “-o” becomes “-ue”;
• the “-u” becomes “-ue”.

Verbs with an “-ie” diphthong

When the final “-e” of the verb stem has a tonic accent, the diphthong in “-ie” is applied.

The root of verbs in this category change like the verb “pensar” (to think).

	Present tense	Present subjunctive	Imperative
Yo	pienso	piense	–
Tú	piensas	pienses	piensa
Él, ella, Usted	piensa	piense	piense
Nosotros, nosotras	pensamos	pensemos	pensemos
Vosotros, vosotras	pensáis	penséis	pensad
Ellos, ellas, Ustedes	piensan	piensen	piensen

Verbs with a diphthong in “-ue”

When the final “-o” of the verb stem has a tonic accent, the diphthong in “-ue” is applied.

The radical of verbs in this category changes like the verb “contar” (to count).

	Present tense	Present subjunctive	Imperative
Yo	cuento	cuente	–
Tú	cuentas	cuentes	cuente
Él, ella, Usted	cuenta	cuente	cuente
Nosotros, nosotras	contamos	contemos	contemos
Vosotros, vosotras	contáis	contéis	contad
Ellos, ellas, Ustedes	cuentan	cuenten	cuenten

Be careful, a verb can never start with a diphthong.

Verbs that diphthong at the first vowel change their spelling. They take an “h-” as the first letter.

Example:

• Oler (to smell) → Yo huelo

The verb “jugar” (to play) is the only verb where the “-u” in the stem changes to “-ue”.

It follows the conjugation pattern of the verb “contar” (to count).

Weakening verbs

Like the diphthong, weakening is a modification that applies to the root of certain verbs.

The “-e” of the verb root is transformed into “-ie”:

• in the third person singular (“yo”; “tú”; “él”, “ella”, “usted”) and the third person plural (“ellos”, “ellas”, “ustedes”) in the present tense ;
• in the third person singular (“él”, “ella”, “usted”) and in the third person plural (“ellos”, “ellas”, “ustedes”) in the past simple;
• in all persons of the present subjunctive tense ;
• in all persons of the imperfect subjunctive tense;
• in all persons of the future subjunctive tense
• in all persons of the imperative ;
• in the gerund.

Verbs with a weakening in « -i »

The radical of the verbs in this category change like the verb “pedir” (to ask).

	Present tense	Simple past tense	Present subjunctive	Imperfect subjunctive	Future subjunctive	Imperative
Yo	pido	pedí	pida	pidiera / pidiese	pidiere	–
Tú	pides	pediste	pidas	pidieras / pidieses	pidieres	pide
Él, ella, Usted	pide	pidió	pida	pidiera / pidiese	pidiere	pida
Nosotros, nosotras	pedimos	pedimos	pidamos	pidiéramos / pidiésemos	pidiéremos	pidamos
Vosotros, vosotras	pedís	pedisteis	pidáis	pidierais / pidieseis	pidiereis	pedid
Ellos, ellas, Ustedes	piden	pidieron	pidan	pidieran / pidiesen	pidieren	pidan

Gerund

pidiendo

Verbs that weaken in “-y

Verbs that end in “-uir” become weaker. This means that the “-i” of their root changes to “-y”.

The stem of verbs in this category changes like the one of the verb “construir” (to build).

	Present tense	Simple past tense	Present subjunctive	Imperfect subjunctive	Future subjunctive	Imperative
Yo	construyo	construí	construya	construyera / construyese	construyere	–
Tú	construyes	construiste	construyas	construyeras / construyeses	construyeres	construye
Él, ella, Usted	construye	construyó	construya	construyera / construyese	construyere	construya
Nosotros, nosotras	construimos	construimos	construyamos	construyéramos / construyésemos	construyéremos	construyamos
Vosotros, vosotras	construís	construisteis	construyáis	construyerais / construyeseis	construyereis	construyid
Ellos, ellas, Ustedes	construyen	construyeron	construyan	construyeran / construyesen	construyeren	construyan

Gerund

construyendo

Verbs that weaken in « -i »

The “-e” in the root of verbs ending in “-eír” or “eñir” weaken to “-i”.

The radical of the verbs in this category change like the verb “teñir” (to dye).

	Present tense	Simple past tense	Present subjunctive	Imperfect subjunctive	Future subjunctive	Imperative
Yo	tiño	teñí	tiña	tiñera / tiñese	tiñere	–
Tú	tiñes	teñiste	tiñas	tiñeras / tiñeses	tiñeres	tiñe
Él, ella, Usted	tiñe	tiñó	tiña	tiñera / tiñese	tiñere	tiña
Nosotros, nosotras	teñimos	teñimos	tiñamos	tiñéramos / tiñésemos	tiñéremos	tiñamos
Vosotros, vosotras	teñís	teñisteis	tiñáis	tiñerais / tiñeseis	tiñereis	teñid
Ellos, ellas, Ustedes	tiñen	tiñeron	tiñan	tiñeran / tiñesen	tiñeren	tiñan

Gerund

tiñendo

Alternating verbs

These are verbs that alternate between diphthong and weakening.

They diphthong in the three persons singular (“yo”; “tú”; “él”, “ella”, “usted”) as well as in the third person plural (“ellos”, “ellas”, “ustedes”) in the present tense modes (indicative, subjunctive, imperative)

They weaken :

• in the first two persons plural (“nosotros”, “nosotras”; “vosotros”, “vosotras”) in the Present subjunctive ;
• in the third person singular and plural (“él”, “ella”, “usted”; “ellos”, “ellas”, “ustedes”) in the Simple past tense;
• in the first person plural (“nosotros”, “nosotras”) in the Imperative ;
• in Gerund.

There are two forms of alternation:

• the final “-e” becomes “-ie” and “-i”;
• the final “-o” becomes “-ue” and “-u”.

The alternation in “-ie” and “-e

The radical of the verbs in this category change like the verb “preferir” (to prefer).

	Present tense	Simple past tense	Present subjunctive	Imperfect subjunctive	Future subjunctive	Imperative
Yo	prefiero	preferí	prefiera	prefiriera / prefiriese	prefiriere	–
Tú	prefieres	preferiste	prefieras	prefirieras / prefirieses	prefirieres	prefiere
Él, ella, Usted	prefiere	prefirió	prefiera	prefiriera / prefiriese	prefiriere	prefiera
Nosotros, nosotras	preferimos	preferimos	prefiramos	prefiriéramos / prefiriésemos	prefiriéremos	prefiramos
Vosotros, vosotras	preferís	preferisteis	prefiráis	prefirierais / prefirieseis	prefiriereis	preferid
Ellos, ellas, Ustedes	prefieren	prefirieron	prefieran	prefirieran / prefiriesen	prefirieren	prefieran

Gerund

prefiriendo

The alternation in « -ue » and « -u »

The radical of the verbs in this category change like the verb “dormir” (to sleep).

	Present tense	Simple past tense	Present subjunctive	Imperfect subjunctive	Future subjunctive	Imperative
Yo	duermo	dormí	durmiera / durmiese	durmiere	–
Tú	duermes	dormiste	durmieras / durmieses	durmieres	duerme
Él, ella, Usted	duerme	durmió	duerme	durmiera / durmiese	durmiere	duerma
Nosotros, nosotras	dormimos	dormimos	durmamos	durmiéramos / durmiésemos	durmiéremos	duermamos
Vosotros, vosotras	dormís	dormisteis	durmáis	durmierais / durmieseis	durmiereis	dormid
Ellos, ellas, Ustedes	duermen	durmieron	duerman	durmieran / durmiesen	durmieren	duerman

Gerund

durmiendo

Verbs in “-acer”, “-ecer”, “-ocer” and “-ucir

The root of verbs in “-acer”, “-ecer”, “-ocer” and “-ucir” are transformed. Their “-c” becomes “-zc”:

• in the first person singular (“yo”) in the Present tense ;
• in all persons of the Present subjunctive ;
• in the third person singular (“él”, “ella”, “Usted”); in the first and third person plural (“nosotros”, “nosotras”; “ellos”, “ellas”, “Ustedes”) in the Imperative.

The radical of the verbs in this category change like the verb “nacer” (to be born).

	Present tense	Present subjunctive	Imperative
Yo	nazco	nazca	–
Tú	naces	nazcas	nace
Él, ella, Usted	nace	nazca	nazcamos
Nosotros, nosotras	nacemos	nazcamos	nazcamos
Vosotros, vosotras	nacéis	nazcáis	naced
Ellos, ellas, Ustedes	nacieron	nazcan	nazcan

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