Learn Hardcore Japanese: kono eiga ha mizikai desu.

In Japanese, は marks the topic of the sentence—what you are talking about. Here, この映画は literally means “As for this movie…,” and then you state something about it (that it’s short). If you used が (この映画が短いです), it would mark 映画 as the grammatical subject and often shifts the nuance toward “this is the movie that’s short” or highlights it among others. For a simple description of a known topic, は is the natural choice.

What does この mean, and how is it different from その or あの?

この is a demonstrative adjective meaning “this (something close to the speaker)”.

その means “that (something close to the listener)”.
あの means “that (something far from both speaker and listener)”.
Here, この映画 = “this movie (we’re talking about right now).”

Why is 短い placed before です, and what does 短いです represent?

短い is an i-adjective (“short”). In polite Japanese, you can attach です after an i-adjective to make it polite. So:
・短い = plain i-adjective (“short”)
・ 短いです = polite present affirmative (“is short”).
Word order: [topic] + [adjective + です] = “As for X, it is Y.”

What kind of adjective is 短い, and how do Japanese adjectives differ from English?

短い is an i-adjective, one of two adjective types in Japanese:

i-adjectives (end in い in their dictionary form), which can directly modify nouns or serve as predicates.
na-adjectives (require な when they modify a noun).
Japanese adjectives inflect (change form) for tense and politeness, so you don’t need a separate verb like “to be”—the adjective itself carries the meaning.

Do we always need です at the end? When can it be omitted?

You don’t always need です.
• です makes a sentence polite.
• In casual speech or writing among friends/family, you can drop です and say この映画は短い.
• In very informal contexts, you might even drop the い and say この映画短い (spoken style).

How would you say “short movie” as a noun phrase instead of a full sentence?

To turn the idea into an attributive phrase (modifying 映画), place the adjective directly before the noun without です:
• 短い映画 = “a short movie.”
If you need politeness when describing the noun in a clause, you’d use な-adjectives or other structures, but basic i-adjectives stay the same.

Why isn’t the sentence この映画が短いです?

While が marks the grammatical subject, using it here changes the nuance.
• この映画は短いです (topic-marking は) = “As for this movie, it is short.” (general statement)
• この映画が短いです (subject-marking が) = often implies “This movie (and not others) is short” or answers a question like “Which movie is short?” In everyday description, は is preferred.

Why are there spaces between the words in this example?

Standard written Japanese doesn’t use spaces; words run together. In learning materials, spaces are sometimes inserted to help beginners see word boundaries and particles clearly. Once you’re comfortable, you read without relying on spaces.