Demostrar Examples, Sentences & Quiz in Spanish

demostrar means "to demonstrate" in English, and this page shows you how it actually sounds in everyday Spanish — not just the conjugation table, but the verb in real sentences, in short dialogues, and in the mistakes learners make with 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. Below you will find twelve example sentences grouped by use, two short dialogues, the most common mistakes with corrections, and a ten-question quiz with explained answers. If you want the full tables first, start with the full conjugation of demostrar; if you want to study one tense in depth, see the demostrar present tense page.

demostrar in everyday use: examples with translations

Everyday present uses

How the verb sounds in the present, the future and in hypotheticals — the forms you will use most often.

  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. Mañana, tú demostrarás su afecto con un regalo — "Tomorrow, you will demonstrate his affection with a gift"
  4. Yo demostraría su inocencia ante el juez si pudiera — "I would demonstrate his innocence before the judge if I could"

Talking about the past

The same verb in the past: one finished action, a habit, something that has just happened, and something that had already happened.

  1. Ayer, yo demostré su talento en el escenario — "Yesterday, I demonstrated his talent on stage"
  2. Antes, nosotros demostrábamos la teoría con un experimento — "Before, we used to demonstrate the theory with an experiment"
  3. Él ha demostrado su afecto con un regalo — "He has demonstrated his affection with a gift"
  4. Yo ya había demostrado su inocencia ante el juez antes de salir — "I already had demonstrated his innocence before the judge before leaving"

Wishes, conditions and commands

The verb after espero que, in si clauses, as a command — and in the conditional perfect, for what would have happened.

  1. Espero que él demuestre su talento en el escenario — "I hope he demonstrates his talent on stage"
  2. Si yo demostrara la teoría con un experimento, todo cambiaría — "If I demonstrated the theory with an experiment, everything would change"
  3. Demuestra su afecto con un regalo. — "Demonstrate his affection with a gift."
  4. Yo habría demostrado su inocencia ante el juez con más tiempo — "I would have demonstrated his innocence before the judge with more time"

demostrar in conversation

Two short dialogues that use demostrar the way people really speak it. Notice how the verb changes with the person, and how the same verb fits different situations.

Two friends talk about it.

  • Lucía: Hola, ¿qué tal? — "Hello, how are you?"
  • Lucía: Yo demuestro su talento en el escenario — "I demonstrate his talent on stage"
  • Marcos: Él demuestra la teoría con un experimento — "He demonstrates the theory with an experiment"
  • Lucía: Ayer, yo demostré su afecto con un regalo — "Yesterday, I demonstrated his affection with a gift"
  • Marcos: Mañana, tú demostrarás su inocencia ante el juez — "Tomorrow, you will demonstrate his innocence before the judge"

A practical exchange.

  • Marcos: Hola, ¿qué tal? — "Hello, how are you?"
  • Marcos: Demuestra interés por el proyecto. — "Demonstrate interest in the project."
  • Lucía: Él ha demostrado su talento en el escenario — "He has demonstrated his talent on stage"
  • Marcos: Espero que él demuestre la teoría con un experimento — "I hope he demonstrates the theory with an experiment"
  • Lucía: Antes, yo demostraba su afecto con un regalo — "Before, I used to demonstrate his affection with a gift"

Common mistakes with demostrar

The errors learners actually make with demostrar, each with the wrong form, the right form, and why the right form is right.

✗ *Yo demostro su inocencia ante el juez.

✓ Correct: Yo demuestro su inocencia ante el juez.

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.

✗ *Espero que él demuestra su inocencia ante el juez

✓ Correct: Espero que él demuestre su inocencia ante el juez

After espero que, Spanish requires the subjunctive: Espero que él demuestre su inocencia ante el juez — not the indicative Espero que él demuestra su inocencia ante el juez.

✗ *Ayer, yo demuestro interés por el proyecto

✓ Correct: Ayer, yo demostré interés por el proyecto

Ayer points to a finished action in the past, so it needs the preterite: Ayer, yo demostré interés por el proyecto.

✗ *De niño, yo demostré su talento en el escenario todos los días

✓ Correct: De niño, yo demostraba su talento en el escenario todos los días

For a repeated habit in the past, use the imperfect, not the preterite: De niño, yo demostraba su talento en el escenario todos los días.

✗ *Yo demuestro en su afecto con un regalo.

✓ Correct: Yo demuestro su afecto con un regalo.

demostrar takes this complement directly, with no preposition: Yo demuestro su afecto con un regalo.

Quiz: demostrar in use

Ten questions on demostrar — its forms, its tenses and its everyday use. Choose the best answer for each one, then check the answer key below, where every answer is explained.

  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: Ayer, yo ______ la teoría con un experimento — "Yesterday, I demonstrated the theory with an experiment" (preterite) A. demostró B. demostramos C. demostré D. demostraste

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

  4. Complete the sentence: Mañana, tú ______ su inocencia ante el juez — "Tomorrow, 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: Él ______ su talento en el escenario — "He has demonstrated his talent on stage" (present perfect) A. hemos demostrado B. ha demostrado C. he demostrado D. has demostrado

  7. Complete the sentence: Espero que él ______ la teoría con un experimento — "I hope he demonstrates the theory with an experiment" (present subjunctive) A. demuestre B. demuestres C. demostremos D. demostréis

  8. Complete the sentence: ______ su afecto con un regalo. — "Demonstrate his affection with a gift." (affirmative imperative) A. demostrad B. demuestra C. demuestre D. demostremos

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

  10. What does demostrar mean in English? A. to show B. to enjoy C. to cross D. to demonstrate

Answer key

  1. demuestro — The present form for yo is demuestro.
  2. demostré — The preterite form for yo is demostré.
  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. ha demostrado — The present perfect form for él/ella/Ud. is ha demostrado.
  7. demuestre — The present subjunctive form for él/ella/Ud. is demuestre.
  8. demuestra — The affirmative imperative form is demuestra.
  9. demostrando — The gerund of demostrar is demostrando: estoy demostrando. The participle demostrado is used with haber instead.
  10. to demonstrate — demostrar means to demonstrate.

Frequently asked questions

What does demostrar mean in English?

demostrar means to demonstrate. For example: 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.

What preposition goes with demostrar?

demostrar takes its complement directly, with no preposition, as in the examples above. Adding an extra preposition is a common learner error.

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.

How do I practise demostrar?

Start with the present tense table on the full conjugation page, then drill the preterite and the imperfect, since those two past tenses cause the most mistakes. Try the Spanish Verb Quiz to test the forms under pressure, and come back to the sentences above until you can say them without looking.

Related links