Den tolfte oktober kan vi inte komma, eftersom vi redan har andra planer.

In Swedish, dates are normally said with an ordinal number, not a cardinal number.

So:

• tolv = twelve
• tolfte = twelfth

That is why Swedish uses den tolfte oktober for a calendar date.

A very literal breakdown is:

• den = the
• tolfte = twelfth
• oktober = October

So Swedish is structurally closer to the twelfth of October than to October twelve.

In Swedish, a full spoken date is very often formed as den + ordinal + month:

• den första maj
• den tredje juni
• den tolfte oktober

So den is part of the normal date pattern here. You will also see dates written numerically, like 12 oktober, especially in writing, but when the date is said out loud, den is very common and natural.

Tolfte is the ordinal form of tolv.

Compare:

• ett → första
• två → andra
• tre → tredje
• tolv → tolfte

So this is just the Swedish word for twelfth. Dates use these ordinal forms.

Because in Swedish, months are not normally capitalized.

So Swedish writes:

• oktober
• november
• december

The same goes for days of the week:

• måndag
• tisdag

This is different from English, where October and Monday must be capitalized.

This is because Swedish follows the V2 rule in main clauses: the finite verb usually comes in the second position.

Here, the sentence begins with the date expression:

• Den tolfte oktober = first element

So the finite verb must come next:

• kan

Then the subject comes after it:

• vi

So the order becomes:

• Den tolfte oktober kan vi inte komma

If you did not start with the date, you could say:

• Vi kan inte komma den tolfte oktober

That version is also correct. It is just less focused on the date.

In this main clause, the pattern is:

• first element
• finite verb
• subject
• inte
• infinitive

So:

• Den tolfte oktober / kan / vi / inte / komma

If the sentence started with the subject, it would be:

• Vi kan inte komma

So inte is in a normal position here. It comes after the finite verb and after the subject in this kind of main clause structure.

Yes, absolutely.

Both are correct:

• Den tolfte oktober kan vi inte komma
• Vi kan inte komma den tolfte oktober

The difference is mainly focus:

• Den tolfte oktober kan vi inte komma puts more emphasis on the date
• Vi kan inte komma den tolfte oktober is a more neutral statement

Swedish often moves a time expression to the front when that information is important in the conversation.

Because eftersom introduces a subordinate clause, and Swedish word order changes in subordinate clauses.

In a subordinate clause, adverbs like inte, redan, alltid, ofta often come before the finite verb.

So:

• eftersom vi redan har andra planer

Compare a main clause:

• Vi har redan andra planer

But after eftersom, the subordinate-clause order is natural:

• eftersom vi redan har andra planer

This is a very important Swedish pattern.

Not in this sentence.

Here eftersom means because/since.

So:

• eftersom vi redan har andra planer = because we already have other plans

English speakers often try to use för att for because, but för att usually means in order to, or sometimes that after certain verbs.

So:

• correct here: eftersom or därför att
• not natural here: för att

No. In this sentence, andra means other.

So:

• andra planer = other plans

This can be confusing, because andra can also mean second in other contexts:

• den andra dagen = the second day

But here, with planer, it clearly means other.

Because the sentence is talking about some other plans, not the other plans.

So:

• andra planer = other plans, nonspecific
• de andra planerna = the other plans, specific

Here the speaker is simply saying they already have other plans in general, so the indefinite form is the natural choice.

Not always.

The comma in:

• Den tolfte oktober kan vi inte komma, eftersom vi redan har andra planer.

is acceptable, but Swedish often uses fewer commas than English. Many writers would also write:

• Den tolfte oktober kan vi inte komma eftersom vi redan har andra planer.

So the comma is more a matter of style, rhythm, or clarity than a strict requirement in a sentence like this.