Questions & Answers about Мы смотрели этот старый фильм.
Why do we use the imperfective verb смотрели here instead of the perfective посмотрели?
The English translation is 'were watching', which describes an ongoing, continuous action in the past. In Russian, ongoing actions use the imperfective aspect. If the sentence meant 'We watched the movie' as a single completed event from start to finish, you would use the perfective verb посмотрели.
фильм is the direct object being watched. Why doesn't its ending change?
As the direct object, фильм is in the accusative case. However, because it is a masculine, inanimate (non-living) noun, its accusative form looks exactly the same as its basic dictionary form.
Why do the words этот and старый also look like they are in their dictionary forms?
Words that describe a noun must match its gender, number, and case. Since фильм is in the masculine inanimate accusative case, its modifiers (этот and старый) also take that form, which happens to look identical to their basic nominative forms.
What does the -и at the end of смотрели tell us?
In the past tense, Russian verbs change based on the gender and number of the subject. Because Мы (we) is plural, the verb takes the plural past tense ending -и.