Demostrar Conjugation in Spanish

The Spanish verb demostrar means to demonstrate, and it is a verb you will use again and again once you know it. Demostrar means to demonstrate or to prove: you demonstrate a theory with evidence, or you demonstrate a feeling with actions. It is stronger and more formal than mostrar. Like every Spanish verb, demostrar 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 Yo demuestro su talento en el escenario — "I demonstrate his talent on stage". 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.

The stem vowel changes in the stressed forms of the present: demuestro, demuestras, demuestra and demuestran — but nosotros and vosotros keep the plain stem: demostramos, demostráis.

Quick facts

  • Infinitive: demostrar
  • English: to demonstrate
  • Verb type: stem-changing -ar verb (o → ue)
  • Ending: -ar
  • Gerund: demostrando
  • Past participle: demostrado
  • Auxiliary verb: haber (all perfect tenses are formed with haber + demostrado)

Pronunciation is not listed on this page: the verified tables do not include IPA for demostrar, so no pronunciation is given rather than an invented one.

Full conjugation tables

Every form below comes from the verified conjugation tables for demostrar. The imperfect subjunctive is shown in its -ra forms; the -se forms use the same stem.

Present indicative

| Person | Form | |---|---|---| | yo | demuestro | | tú | demuestras | | él/ella/Ud. | demuestra | | nosotros/as | demostramos | | vosotros/as | demostráis | | ellos/ellas/Uds. | demuestran |

Preterite

| Person | Form | |---|---|---| | yo | demostré | | tú | demostraste | | él/ella/Ud. | demostró | | nosotros/as | demostramos | | vosotros/as | demostrasteis | | ellos/ellas/Uds. | demostraron |

Imperfect

| Person | Form | |---|---|---| | yo | demostraba | | tú | demostrabas | | él/ella/Ud. | demostraba | | nosotros/as | demostrábamos | | vosotros/as | demostrabais | | ellos/ellas/Uds. | demostraban |

Future

| Person | Form | |---|---|---| | yo | demostraré | | tú | demostrarás | | él/ella/Ud. | demostrará | | nosotros/as | demostraremos | | vosotros/as | demostraréis | | ellos/ellas/Uds. | demostrarán |

Conditional

| Person | Form | |---|---|---| | yo | demostraría | | tú | demostrarías | | él/ella/Ud. | demostraría | | nosotros/as | demostraríamos | | vosotros/as | demostraríais | | ellos/ellas/Uds. | demostrarían |

Present perfect

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

Pluperfect

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

Future perfect

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

Conditional perfect

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

Present subjunctive

| Person | Form | |---|---|---| | yo | demuestre | | tú | demuestres | | él/ella/Ud. | demuestre | | nosotros/as | demostremos | | vosotros/as | demostréis | | ellos/ellas/Uds. | demuestren |

Imperfect subjunctive (-ra)

| Person | Form | |---|---|---| | yo | demostrara | | tú | demostraras | | él/ella/Ud. | demostrara | | nosotros/as | demostráramos | | vosotros/as | demostrarais | | ellos/ellas/Uds. | demostraran |

Imperative (affirmative)

| Person | Form | |---|---|---| | tú | demuestra | | él/ella/Ud. | demuestre | | nosotros/as | demostremos | | vosotros/as | demostrad | | ellos/ellas/Uds. | demuestren |

Imperative (negative)

| Person | Form | |---|---|---| | tú | demuestres | | él/ella/Ud. | demuestre | | nosotros/as | demostremos | | vosotros/as | demostréis | | ellos/ellas/Uds. | demuestren |

Gerund and past participle

Form Spanish Use
Gerund demostrando with estar for the progressive: está demostrando
Past participle demostrado with haber for the perfect tenses: he demostrado

How to use each tense

Present indicative

Use the present for routines, general facts and what is happening right now. The stem vowel changes in the stressed forms of the present: demuestro, demuestras, demuestra and demuestran — but nosotros and vosotros keep the plain stem: demostramos, demostráis. For demostrar, the present indicative looks like this in a real sentence: Yo demuestro su talento en el escenario — "I demonstrate his talent on stage".

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 demostrar, the preterite looks like this in a real sentence: Ayer, yo demostré la teoría con un experimento — "Yesterday, I demonstrated the theory with an experiment".

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 demostrar, the imperfect looks like this in a real sentence: De niño, yo demostraba su afecto con un regalo — "As a child, I used to demonstrate his affection with a gift".

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 demostrar, the future looks like this in a real sentence: Mañana, yo demostraré su inocencia ante el juez — "Tomorrow, I will demonstrate his innocence before the judge".

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 demostrar, the conditional looks like this in a real sentence: Yo demostraría su talento en el escenario si pudiera — "I would demonstrate his talent on stage if I could".

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 demostrar, the present perfect looks like this in a real sentence: Hoy, yo he demostrado la teoría con un experimento — "Today, I have demonstrated the theory with an experiment".

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 demostrar, the pluperfect looks like this in a real sentence: Yo ya había demostrado su afecto con un regalo antes de salir — "I already had demonstrated his affection with a gift before leaving".

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 demostrar, the future perfect looks like this in a real sentence: Para mañana, yo habré demostrado su inocencia ante el juez — "By tomorrow, I will have demonstrated his innocence before the judge".

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 demostrar, the conditional perfect looks like this in a real sentence: Yo habría demostrado su talento en el escenario con más tiempo — "I would have demonstrated his talent on stage with more time".

Present subjunctive

Use the present subjunctive after expressions of wish, doubt, emotion and hope, such as espero que or quiero que. The stem vowel changes in the stressed forms of the present: demuestro, demuestras, demuestra and demuestran — but nosotros and vosotros keep the plain stem: demostramos, demostráis. For demostrar, the present subjunctive looks like this in a real sentence: Espero que él demuestre la teoría con un experimento — "I hope he demonstrates the theory with an experiment".

Imperfect subjunctive (-ra)

Use the imperfect subjunctive after past wishes and in si clauses about the past. The -ra forms are 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 demostrar, the imperfect subjunctive (-ra) looks like this in a real sentence: Si yo demostrara su afecto con un regalo, todo cambiaría — "If I demonstrated his affection with a gift, everything would change".

Imperative (affirmative)

Use the affirmative imperative for direct commands, instructions and invitations. The stem vowel changes in the stressed forms of the present: demuestro, demuestras, demuestra and demuestran — but nosotros and vosotros keep the plain stem: demostramos, demostráis. For demostrar, the imperative (affirmative) looks like this in a real sentence: Demuestra su inocencia ante el juez. — "Demonstrate his innocence before the judge.".

Imperative (negative)

Use the negative imperative, always with no, to tell someone not to do something. The stem vowel changes in the stressed forms of the present: demuestro, demuestras, demuestra and demuestran — but nosotros and vosotros keep the plain stem: demostramos, demostráis. For demostrar, the imperative (negative) looks like this in a real sentence: No demuestres su talento en el escenario. — "Do not demonstrate his talent on stage.".

Example sentences

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

  1. Yo demuestro su talento en el escenario — "I demonstrate his talent on stage"
  2. Mi amigo demuestra la teoría con un experimento — "My friend demonstrates the theory with an experiment"
  3. Ayer, yo demostré su afecto con un regalo — "Yesterday, I demonstrated his affection with a gift"
  4. Antes, nosotros demostrábamos su inocencia ante el juez — "Before, we used to demonstrate his innocence before the judge"
  5. Mañana, tú demostrarás interés por el proyecto — "Tomorrow, you will demonstrate interest in the project"
  6. Yo demostraría su talento en el escenario si tuviera más tiempo — "I would demonstrate his talent on stage if I had more time"
  7. Él ha demostrado la teoría con un experimento — "He has demonstrated the theory with an experiment"
  8. Espero que él demuestre su afecto con un regalo — "I hope he demonstrates his affection with a gift"
  9. Yo ya había demostrado su inocencia ante el juez antes de salir — "I already had demonstrated his innocence before the judge before leaving"
  10. Ellos demostraban interés por el proyecto cuando eran jóvenes — "They used to demonstrate interest in the project when they were young"

Common mistakes

  1. Wrong: Yo demostro la teoría con un experimento. — Right: Yo demuestro la teoría con un experimento. — demostrar is a stem-changing verb (o → ue): the stem vowel changes in the stressed present forms, so the yo form is demuestro, not demostro.
  2. Wrong: Espero que él demuestra la teoría con un experimento — Right: Espero que él demuestre la teoría con un experimento — After espero que, Spanish requires the subjunctive: Espero que él demuestre la teoría con un experimento — not the indicative Espero que él demuestra la teoría con un experimento.
  3. Wrong: Ayer, yo demuestro su afecto con un regalo — Right: Ayer, yo demostré su afecto con un regalo — Ayer points to a finished action in the past, so it needs the preterite: Ayer, yo demostré su afecto con un regalo.
  4. Wrong: De niño, yo demostré su inocencia ante el juez todos los días — Right: De niño, yo demostraba su inocencia ante el juez todos los días — For a repeated habit in the past, use the imperfect, not the preterite: De niño, yo demostraba su inocencia ante el juez todos los días.
  5. Wrong: Yo demuestro en su talento en el escenario. — Right: Yo demuestro su talento en el escenario. — demostrar takes this complement directly, with no preposition: Yo demuestro su talento en el escenario.

Quiz: test yourself

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

  1. Complete the sentence: Yo ______ su talento en el escenario — "I demonstrate his talent on stage" (present) A. demuestras B. demuestra C. demostramos D. demuestro

  2. Complete the sentence: Él ______ la teoría con un experimento — "He demonstrated the theory with an experiment" (preterite) A. demostró B. demostré C. demostraste D. demostramos

  3. Complete the sentence: Nosotros ______ su afecto con un regalo — "We used to demonstrate his affection with a gift" (imperfect) A. demostraba B. demostrabas C. demostrabais D. demostrábamos

  4. Complete the sentence: Tú ______ su inocencia ante el juez — "You will demonstrate his innocence before the judge" (future) A. demostraré B. demostrará C. demostraremos D. demostrarás

  5. Complete the sentence: Yo ______ interés por el proyecto — "I would demonstrate interest in the project" (conditional) A. demostraría B. demostrarías C. demostraríamos D. demostraríais

  6. Complete the sentence: Espero que él ______ su talento en el escenario — "I hope he demonstrates his talent on stage" (present subjunctive) A. demuestres B. demostremos C. demostréis D. demuestre

  7. Complete the sentence: Si yo ______ la teoría con un experimento, todo cambiaría — "If I demonstrated the theory with an experiment, everything would change" (imperfect subjunctive) A. demostrara B. demostraras C. demostráramos D. demostrarais

  8. Complete the sentence: Nosotros ______ su afecto con un regalo — "We have demonstrated his affection with a gift" (present perfect) A. hemos demostrado B. he demostrado C. has demostrado D. ha demostrado

  9. Complete the sentence: No ______ su inocencia ante el juez. — "Do not demonstrate his innocence before the judge." (negative imperative) A. demuestre B. demostremos C. demostréis D. demuestres

  10. Which is the gerund of demostrar, used with estar for the progressive? A. demostré B. demostrando C. demostrado D. demuestro

Answer key

  1. demuestro — The present form for yo is demuestro.
  2. demostró — The preterite form for él/ella/Ud. is demostró.
  3. demostrábamos — The imperfect form for nosotros/as is demostrábamos.
  4. demostrarás — The future form for tú is demostrarás.
  5. demostraría — The conditional form for yo is demostraría.
  6. demuestre — The present subjunctive form for él/ella/Ud. is demuestre.
  7. demostrara — The imperfect subjunctive form for yo is demostrara.
  8. hemos demostrado — The present perfect form for nosotros/as is hemos demostrado.
  9. demuestres — The negative imperative form is demuestres.
  10. demostrando — The gerund of demostrar is demostrando: estoy demostrando. The participle demostrado is used with haber instead.

Frequently asked questions

What does demostrar mean in English?

demostrar means to demonstrate. It is used in everyday situations such as Yo demuestro su talento en el escenario — "I demonstrate his talent on stage". The exact English wording depends on the context, but the core meaning stays the same across the tenses.

Is demostrar regular?

No. demostrar is a stem-changing -ar verb (o → ue). The stem vowel changes in the stressed forms of the present: demuestro, demuestras, demuestra and demuestran — but nosotros and vosotros keep the plain stem: demostramos, demostráis. The nosotros and vosotros forms keep the plain stem, which is the part learners most often get right by accident.

What is the gerund and the past participle of demostrar?

The gerund is demostrando and the past participle is demostrado. Use the gerund with estar for the progressive, and the participle with haber for the perfect tenses.

How do I say "I demonstrate" in the past?

It depends on the kind of past. For one finished action, use the preterite: Ayer, yo demostré la teoría con un experimento — "Yesterday, I demonstrated the theory with an experiment". For a repeated habit or background in the past, use the imperfect: De niño, yo demostraba su afecto con un regalo — "As a child, I used to demonstrate his affection with a gift". For something that has just happened, use the present perfect: Hoy, yo he demostrado la teoría con un experimento — "Today, I have demonstrated the theory with an experiment".

What is the difference between demostrar and mostrar?

Mostrar is simply to show something. Demostrar is to show it with proof or with evidence — you demuestras tu inocencia, but muestras tu pasaporte. Demostrar means to demonstrate or to prove: you demonstrate a theory with evidence, or you demonstrate a feeling with actions. It is stronger and more formal than mostrar.

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