Si compres sucre, compra també sal.

In Catalan, si without an accent means if.

• si = if
• sí = yes

So in Si compres sucre, compra també sal, the word is si because it introduces a condition.

Compres is the 2nd person singular present indicative form of comprar (to buy).

So:

• jo compro = I buy
• tu compres = you buy
• ell/ella compra = he/she buys

After si meaning if, Catalan normally uses the indicative, not the imperative. So si compres means if you buy.

Because the two verbs do different jobs:

• compres = you buy → a normal present-tense verb in the if-clause
• compra = buy! → the imperative form, giving an instruction

So the structure is:

• Si compres sucre = if you buy sugar
• compra també sal = buy salt too

This is very natural in Catalan: a condition first, then a command.

Because compres is not the normal affirmative command form for tu.

For comprar, the affirmative imperative for tu is:

• compra! = buy!

Not:

• compres! ✗

A useful pattern is:

• present indicative tu: compres
• imperative tu: compra

For many -ar verbs, the tu imperative looks like the ell/ella present form:

• parles → parla!
• escoltes → escolta!
• compres → compra!

Catalan usually leaves out subject pronouns when they are clear from the verb ending.

So instead of saying:

• Si tu compres sucre, compra també sal

Catalan normally says:

• Si compres sucre, compra també sal

The endings already show that the sentence is addressing tu.

Including tu is possible, but it usually adds emphasis or contrast.

It is informal singular, addressed to tu.

That is why you see:

• compres = you buy
• compra = buy!

If you wanted the formal singular (vostè), you would say:

• Si compra sucre, compri també sal.

If you wanted informal plural (vosaltres), you would say:

• Si compreu sucre, compreu també sal.

També means also, too, or as well.

In this sentence, it adds the idea of in addition:

• compra també sal = buy salt too / also buy salt

Its position is natural here, after the verb:

• compra també sal

That is a very common placement in Catalan. It sounds smooth and idiomatic.

Because Catalan often omits the article with mass nouns like sugar and salt when talking about buying some amount of them in a general way.

So:

• compres sucre = you buy sugar
• compra també sal = buy salt too

This is similar to English, where we also usually say buy sugar rather than buy the sugar, unless we mean a specific sugar already known to both speakers.

If you added the article, it would usually sound more specific:

• el sucre = the sugar
• la sal = the salt

The comma is standard and helpful here because the sentence begins with a conditional clause:

• Si compres sucre, ...

Then comes the main clause:

• ..., compra també sal.

In short informal writing, people sometimes leave out commas, but using the comma is the safest and most standard choice.

Not in this kind of sentence.

With a real or likely condition, Catalan normally uses the indicative after si:

• Si compres sucre... = if you buy sugar...

So compres here is indicative, not subjunctive.

For a learner, the important thing is: after si meaning if, Catalan very often uses ordinary tense forms like the present indicative.