Basar Conjugation in Spanish

The Spanish verb basar means to base, and it is a verb you will use again and again once you know it. Basar means to base, and it is the transitive verb for founding an opinion, a theory, a decision or a project on something: you base your opinion on the data, you base a theory on experience. It takes en for the foundation, as in basar mi opinión en los datos. Like every Spanish verb, basar changes its ending for each person and tense, and this page gives you the complete picture: every tense, every person, the gerund and the past participle, all from the verified conjugation tables. For example, in the present tense you say baso mi opinión en los datos, and in the preterite you say basé mi decisión en los hechos. Work through the tables below, read the notes for each tense, and then test yourself with the examples, the common mistakes and the quiz at the end of the page.

Quick facts

  • Infinitive: basar
  • English: to base
  • Verb type: regular -ar verb
  • Ending: -ar
  • Gerund: basando
  • Past participle: basado
  • Auxiliary verb: haber (all perfect tenses are formed with haber + basado)

Pronunciation is not listed on this page: the verified tables do not include IPA for basar, so no pronunciation is given rather than an invented one. Basar takes en for the foundation: baso mi opinión en los datos. To say something is based on something, use the reflexive basarse.

Full conjugation tables

Every form below comes from the verified conjugation tables for basar. The imperfect subjunctive is shown in its -ra forms; the -se forms use the same stem. For reflexive verbs, the pronoun column shows the reflexive pronoun that goes before each form.

Present indicative

Person Form
yo baso
tú basas
él/ella/Ud. basa
nosotros/as basamos
vosotros/as basáis
ellos/ellas/Uds. basan

Preterite

Person Form
yo basé
tú basaste
él/ella/Ud. basó
nosotros/as basamos
vosotros/as basasteis
ellos/ellas/Uds. basaron

Imperfect

Person Form
yo basaba
tú basabas
él/ella/Ud. basaba
nosotros/as basábamos
vosotros/as basabais
ellos/ellas/Uds. basaban

Future

Person Form
yo basaré
tú basarás
él/ella/Ud. basará
nosotros/as basaremos
vosotros/as basaréis
ellos/ellas/Uds. basarán

Conditional

Person Form
yo basaría
tú basarías
él/ella/Ud. basaría
nosotros/as basaríamos
vosotros/as basaríais
ellos/ellas/Uds. basarían

Present perfect

Person Form
yo he basado
tú has basado
él/ella/Ud. ha basado
nosotros/as hemos basado
vosotros/as habéis basado
ellos/ellas/Uds. han basado

Pluperfect

Person Form
yo había basado
tú habías basado
él/ella/Ud. había basado
nosotros/as habíamos basado
vosotros/as habíais basado
ellos/ellas/Uds. habían basado

Future perfect

Person Form
yo habré basado
tú habrás basado
él/ella/Ud. habrá basado
nosotros/as habremos basado
vosotros/as habréis basado
ellos/ellas/Uds. habrán basado

Conditional perfect

Person Form
yo habría basado
tú habrías basado
él/ella/Ud. habría basado
nosotros/as habríamos basado
vosotros/as habríais basado
ellos/ellas/Uds. habrían basado

Present subjunctive

Person Form
yo base
tú bases
él/ella/Ud. base
nosotros/as basemos
vosotros/as baséis
ellos/ellas/Uds. basen

Imperfect subjunctive (-ra)

Person Form
yo basara
tú basaras
él/ella/Ud. basara
nosotros/as basáramos
vosotros/as basarais
ellos/ellas/Uds. basaran

Imperative (affirmative)

Person Form
tú basa
él/ella/Ud. base
nosotros/as basemos
vosotros/as basad
ellos/ellas/Uds. basen

Imperative (negative)

Person Form
tú bases
él/ella/Ud. base
nosotros/as basemos
vosotros/as baséis
ellos/ellas/Uds. basen

Gerund and past participle

Form Spanish Use
Gerund basando with estar for the progressive: estoy basando
Past participle basado with haber for the perfect tenses: he basado

How to use each tense

Present indicative

Use the present for routines, general facts and what is happening right now. For this verb the tense is regular, so the forms follow the standard endings for its verb class. For basar, the present looks like this in a real sentence: Baso mi opinión en los datos. Learn the present forms in the table above alongside this example, and notice how the ending, not the stem, usually carries the meaning of the tense.

Preterite

Use the preterite for finished actions with a clear end, often with ayer, el año pasado or anoche. For this verb the tense is regular, so the forms follow the standard endings for its verb class. For basar, the preterite looks like this in a real sentence: Ayer, basé la teoría en la experiencia. Learn the preterite forms in the table above alongside this example, and notice how the ending, not the stem, usually carries the meaning of the tense.

Imperfect

Use the imperfect for background, habits and actions in progress in the past, often with de niño, antes or mientras. For this verb the tense is regular, so the forms follow the standard endings for its verb class. For basar, the imperfect looks like this in a real sentence: De niño, basaba mi decisión en los hechos. Learn the imperfect forms in the table above alongside this example, and notice how the ending, not the stem, usually carries the meaning of the tense.

Future

Use the future for plans, predictions and promises, often with mañana, el año que viene or pronto. For this verb the tense is regular, so the forms follow the standard endings for its verb class. For basar, the future looks like this in a real sentence: Mañana, basaré el proyecto en un estudio. Learn the future forms in the table above alongside this example, and notice how the ending, not the stem, usually carries the meaning of the tense.

Conditional

Use the conditional for polite requests, hypotheticals and what would happen, often with si clauses. For this verb the tense is regular, so the forms follow the standard endings for its verb class. For basar, the conditional looks like this in a real sentence: Basaría mi opinión en los datos si pudiera. Learn the conditional forms in the table above alongside this example, and notice how the ending, not the stem, usually carries the meaning of the tense.

Present perfect

Use the present perfect for recent actions and experiences, often with hoy, esta semana or ya. For this verb the tense is regular, so the forms follow the standard endings for its verb class. For basar, the present perfect looks like this in a real sentence: Hoy, he basado la teoría en la experiencia. Learn the present perfect forms in the table above alongside this example, and notice how the ending, not the stem, usually carries the meaning of the tense.

Pluperfect

Use the pluperfect when one past action happened before another past action. For this verb the tense is regular, so the forms follow the standard endings for its verb class. For basar, the pluperfect looks like this in a real sentence: Había basado mi decisión en los hechos antes de salir. Learn the pluperfect forms in the table above alongside this example, and notice how the ending, not the stem, usually carries the meaning of the tense.

Future perfect

Use the future perfect for something that will already be finished by a future time. For this verb the tense is regular, so the forms follow the standard endings for its verb class. For basar, the future perfect looks like this in a real sentence: Para mañana, habré basado el proyecto en un estudio. Learn the future perfect forms in the table above alongside this example, and notice how the ending, not the stem, usually carries the meaning of the tense.

Conditional perfect

Use the conditional perfect for what would have happened under different conditions. For this verb the tense is regular, so the forms follow the standard endings for its verb class. For basar, the conditional perfect looks like this in a real sentence: Habría basado mi opinión en los datos con más tiempo. Learn the conditional perfect forms in the table above alongside this example, and notice how the ending, not the stem, usually carries the meaning of the tense.

Present subjunctive

Use the present subjunctive after expressions of wish, doubt, emotion and hope, such as espero que or quiero que. For this verb the tense is regular, so the forms follow the standard endings for its verb class. For basar, the present subjunctive looks like this in a real sentence: Espero que él base la teoría en la experiencia. Learn the present subjunctive forms in the table above alongside this example, and notice how the ending, not the stem, usually carries the meaning of the tense.

Imperfect subjunctive (-ra)

Use the imperfect subjunctive after past wishes and in si clauses about the past, and note the -ra forms shown here; the -se forms use the same stem. For this verb the tense is regular, so the forms follow the standard endings for its verb class. For basar, the imperfect subjunctive looks like this in a real sentence: Si él basara mi decisión en los hechos, todo cambiaría. Learn the imperfect subjunctive forms in the table above alongside this example, and notice how the ending, not the stem, usually carries the meaning of the tense.

Imperative (affirmative)

Use the affirmative imperative for direct commands, instructions and invitations. For this verb the tense is regular, so the forms follow the standard endings for its verb class. For basar, the affirmative imperative looks like this in a real sentence: ¡basa el proyecto en un estudio! Learn the affirmative imperative forms in the table above alongside this example, and notice how the ending, not the stem, usually carries the meaning of the tense.

Imperative (negative)

Use the negative imperative, always with no, to tell someone not to do something. For this verb the tense is regular, so the forms follow the standard endings for its verb class. For basar, the negative imperative looks like this in a real sentence: No bases mi opinión en los datos. Learn the negative imperative forms in the table above alongside this example, and notice how the ending, not the stem, usually carries the meaning of the tense.

Example sentences

Ten natural sentences with basar, covering different tenses and persons. Each one uses a form from the tables above.

  1. Baso mi opinión en los datos. — I base my opinion on the data.
  2. Basa la teoría en la experiencia. — He/she bases the theory on experience.
  3. Ayer, basé mi decisión en los hechos. — Yesterday, I based my decision on the facts.
  4. Antes, nosotros basábamos el proyecto en un estudio. — Before, we used to base the project on a study.
  5. Mañana, tú basarás mi opinión en los datos. — Tomorrow, you will base my opinion on the data.
  6. Yo basaría la teoría en la experiencia si tuviera más tiempo. — I would base the theory on experience if I had more time.
  7. Él ha basado mi decisión en los hechos. — He has based my decision on the facts.
  8. Espero que él base el proyecto en un estudio. — I hope he bases the project on a study.
  9. Yo ya había basado mi opinión en los datos antes de salir. — I had already based my opinion on the data before leaving.
  10. Ellos basaban la teoría en la experiencia cuando eran jóvenes. — They used to base the theory on experience when they were young.

Common mistakes

  1. Wrong: Yo basa mi opinión en los datos. — Right: Yo baso mi opinión en los datos. — The person matters: basa is the él/ella/Ud. form, while the yo form is baso. Using the third-person form with yo is one of the most common beginner errors.
  2. Wrong: Treating basar and basarse as identical in every context. — Right: Basar means to base, while basarse means to be based on something yourself. — They overlap, but each has uses the other does not: basar fits sentences such as Baso mi opinión en los datos, while basarse belongs in a different sentence. Check the meaning you want before choosing.
  3. Wrong: Yo soy basado la teoría en la experiencia. — Right: Yo he basado la teoría en la experiencia. — Spanish perfect tenses use haber, not ser: he basado, has basado, ha basado. Ser plus the participle makes a passive, not a perfect tense.
  4. Wrong: De niño, yo basé mi decisión en los hechos todos los días. — Right: De niño, yo basaba mi decisión en los hechos todos los días. — For a repeated habit in the past, use the imperfect (basaba), not the preterite. The preterite (basé) is for one finished action.

Quiz: test yourself

Ten questions on basar. Choose the right form, then check the answer key below.

  1. Complete the sentence: Yo ___ mi opinión en los datos. (present tense) A. baso B. basas C. basa D. basamos

  2. Complete the sentence: Ayer, él ___ la teoría en la experiencia. (preterite) A. basé B. basaste C. basaron D. basó

  3. Complete the sentence: Antes, nosotros ___ mi decisión en los hechos. (imperfect) A. basabas B. basaban C. basábamos D. basaba

  4. Complete the sentence: Mañana, tú ___ el proyecto en un estudio. (future) A. basaremos B. basarás C. basaré D. basará

  5. Complete the sentence: Yo ___ mi opinión en los datos si pudiera. (conditional) A. basaría B. basarías C. basarían D. baso

  6. Complete the sentence: Espero que él ___ la teoría en la experiencia. (present subjunctive) A. bases B. basemos C. baso D. base

  7. Complete the sentence: Si yo ___ mi decisión en los hechos, todo cambiaría. (imperfect subjunctive, -ra form) A. basáramos B. baso C. basara D. basaras

  8. Complete the sentence: Nosotros ___ el proyecto en un estudio. (present perfect) A. han basado B. hemos basado C. he basado D. has basado

  9. Complete the command: ¡___ mi opinión en los datos! (affirmative imperative, tú) A. basa B. base C. basemos D. basad

  10. Which is the gerund of basar, used with estar for the progressive? A. basado B. baso C. basé D. basando

Answer key

  1. baso — The first-person present of basar is baso. The other options are the tú, él/ella and nosotros forms.
  2. basó — The third-person preterite of basar is basó, the form for a single finished action in the past.
  3. basábamos — The nosotros imperfect of basar is basábamos, used here for a repeated past habit.
  4. basarás — The second-person future of basar is basarás.
  5. basaría — The first-person conditional of basar is basaría, the form for what would happen.
  6. base — After espero que, the subjunctive is required: the third-person present subjunctive of basar is base.
  7. basara — The first-person imperfect subjunctive (-ra) of basar is basara.
  8. hemos basado — The nosotros present perfect of basar is hemos basado: hemos + basado.
  9. basa — The affirmative tú imperative of basar is basa.
  10. basando — The gerund of basar is basando: estoy basando. The participle basado is used with haber instead.

Frequently asked questions

What does basar mean in English?

Basar means to base. It is used in everyday situations such as Baso mi opinión en los datos. The exact English wording depends on the context, but the core meaning stays the same across the tenses.

Is basar regular or irregular?

Basar is a fully regular -ar verb, so every tense follows the standard endings for its class. Once you know the regular pattern, you can produce every form on this page, including baso in the present and basé in the preterite.

What is the difference between basar and basarse?

Basar means to base, while basarse means to be based on something yourself. They are easy to confuse because they appear in similar situations, but they are not interchangeable: use basar when you mean to base, as in Baso mi opinión en los datos, and use basarse for to be based on something yourself. When in doubt, check the object of the sentence — it usually shows which verb fits.

How do I say “I base” in the past?

It depends on the kind of past. For one finished action, use the preterite: yo basé la teoría en la experiencia. For a repeated habit or background in the past, use the imperfect: yo basaba mi decisión en los hechos. For something that has just happened, use the present perfect: yo he basado la teoría en la experiencia.

How do I practise basar?

Start with the present tense table, then drill the preterite and the imperfect, since those two past tenses cause the most mistakes. Try the basar examples and quiz page for more sentences, and use the Spanish Verb Quiz to test the forms under pressure.

Related links