Breakdown of Pienso que la película es buena.
ser
to be
bueno
good
pensar
to think
que
that (relative pronoun, conjunction)
Questions & Answers about Pienso que la película es buena.
Why is it pienso instead of 'penso'?
The verb is pensar (to think). It is a stem-changing verb. When you conjugate it in the present tense, the e in the stem changes to ie for most forms, including the 'I' form (yo pienso). You will also see this change in forms like tú piensas and él piensa, but not in the 'we' form (nosotros pensamos).
Can I leave out the word que like we often do in English?
Why do we use es instead of está for 'is'?
We use es (from the verb ser) because you are describing an inherent quality or characteristic of the movie. Even though this is just your opinion, being 'good' is treated as a core trait of the film itself, so ser is the right choice.
Why is the word for good spelled buena instead of bueno?
Adjectives in Spanish have to match the gender of the noun they describe. Because la película (the movie) is a feminine noun, the adjective must also be the feminine form, which is buena.