Aquest és un cas important.

Aquest means this and is a demonstrative adjective. It points to something near the speaker.

In Aquest és un cas important, aquest goes with cas because cas is masculine singular.

A quick comparison:

• aquest cas = this case
• aquests casos = these cases
• aquesta situació = this situation
• aquestes situacions = these situations

So aquest is there because the sentence is talking about this case.

Because aquest modifies a noun, while això stands alone.

• aquest = this
  • noun
    
    • aquest cas = this case
• això = this by itself
  
  • Això és important = This is important

In your sentence, there is a noun, cas, so Catalan uses aquest, not això.

The accent in és is important because it distinguishes it from es.

• és = is
• es = a reflexive/pronominal form, like himself/herself/itself or part of some verb structures

So in this sentence:

• Aquest és un cas important = This is an important case

The accent tells you this is the verb to be.

És is the 3rd person singular of ser (to be).

The structure is very similar to English:

• Aquest = this
• és = is
• un cas important = an important case

Catalan uses ser here to identify or classify something: this is an important case.

Un is the indefinite article, meaning a/an.

So:

• un cas = a case
• el cas = the case

In Aquest és un cas important, the sentence is classifying it as an important case, not referring to a specific already-known case with the.

In Catalan, adjectives often come after the noun.

So:

• un cas important = an important case

This is one of the first word-order differences English speakers notice. English usually puts adjectives before nouns, but Catalan often places them after.

That said, adjective position in Catalan can sometimes change for style or meaning, but with important, the normal order here is cas important.

Because important already matches the noun correctly, and in this case the masculine singular form is simply important.

With cas (masculine singular), you get:

• un cas important

If the noun were feminine singular, you would still often have:

• una situació important

And in the plural:

• casos importants
• situacions importants

So the main visible change is often in the plural: important → importants.

You usually learn the gender together with the noun.

Here, cas is masculine, which is why it takes:

• aquest
• un

So you get:

• aquest cas
• un cas

If it were a feminine noun, those words would change accordingly.

For example:

• aquesta idea
• una idea

Gender in Catalan is something you mostly memorize noun by noun, though some endings give hints.

A careful Central Catalan pronunciation would be roughly:

ah-KESHT ez oon kahz eem-por-TANT

A few helpful notes:

• aquest often ends with a sound like sht
• és is pronounced like ez
• un is not exactly English oon, but that approximation helps
• cas sounds like kahs or kahz depending on context and accent
• the stress in important falls on the last syllable: im-por-TANT

Pronunciation varies somewhat by dialect, but this approximation is a good start.

Yes, you can, but the meaning changes slightly.

• Aquest és un cas important = This is an important case
• És un cas important = It is an important case / This is an important case, depending on context

Including aquest makes the sentence more explicit and points directly to something: this one.

Yes, very close.

Catalan:

• Aquest = This
• és = is
• un cas important = an important case

So the overall pattern is:

Demonstrative + verb to be + article + noun + adjective

The main difference an English speaker will notice is that the adjective usually comes after the noun in Catalan:

• English: important case
• Catalan: cas important