
demostrar Preterite Conjugation
demostrar — to prove
Demostrar is regular in the preterite: demostré, demostraste, demostró, demostramos, demostrasteis, demostraron.
demostrar Preterite Forms
When to Use the Preterite
Use the preterite to talk about a specific instance where someone proved or demonstrated something, like a scientific result or a point in an argument that is now finished.
Notes on demostrar in the Preterite
Unlike the present tense, demostrar is completely regular in the preterite. There is no 'o' to 'ue' stem change here.
Example Sentences
El científico demostró su teoría con un experimento.
The scientist proved his theory with an experiment.
él/ella/usted
Ayer les demostré que yo tenía razón.
Yesterday I proved to them that I was right.
yo
Los estudiantes demostraron sus habilidades en el examen.
The students demonstrated their skills in the exam.
ellos/ellas/ustedes
Common Mistakes
Mistake: demuestré
Correct: demostré
Why: Learners often try to carry the 'ue' stem change from the present tense into the preterite, but it doesn't belong here.
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Related Tenses
Present
yo: demuestro
Demostrar is an o > ue stem-changing verb in all forms except nosotros and vosotros.
Imperfect
yo: demostraba
Demostrar is regular in the imperfect: demostraba, demostrabas, demostraba, demostrábamos, demostrabais, demostraban.
Future
yo: demostraré
The future of demostrar is regular: demostraré, demostrarás, demostrará, demostraremos, demostraréis, demostrarán.
Conditional
yo: demostraría
The conditional of demostrar is regular: demostraría, demostrarías, demostraría, demostraríamos, demostraríais, demostrarían.
Present Subjunctive
yo: demuestre
Demostrar has a stem change (o > ue) in the subjunctive, except for nosotros and vosotros.
Imperfect Subjunctive
yo: demostrara
The imperfect subjunctive is regular: demostrara, demostraras, demostrara, demostráramos, demostrarais, demostraran.
Affirmative Imperative
yo: demuestra
The imperative uses 'demuestra' (tú) and 'demuestre' (usted), following the o > ue stem change.
Negative Imperative
yo: no demuestres
The negative imperative uses the present subjunctive: no demuestres, no demuestre, no demostremos, no demostréis, no demuestren.