Learn Hardcore German: Ich trinke seltener Kaffee, weil ich sonst schlecht schlafe. - I drink coffee less often because otherwise I sleep badly.

Weil introduces a subordinate clause (Nebensatz). In German, in most subordinate clauses the conjugated verb goes to the end of the clause.

Main clause: Ich trinke seltener Kaffee. → verb in 2nd position: trinke
Subordinate clause: …, weil ich sonst schlecht schlafe. → verb at the end: schlafe

This is a standard rule with conjunctions like weil, dass, wenn, obwohl, damit etc.

Could I say …, weil ich sonst schlecht schlafe with the verb in the second position, like …, weil ich sonst schlafe schlecht?

No. In modern standard German, after weil the finite verb must go to the end:

✅ …, weil ich sonst schlecht schlafe.
❌ …, weil ich sonst schlafe schlecht.

Older or very colloquial speech sometimes uses weil with verb‑second, but that’s not recommended for learners and is still considered incorrect in formal German.

Why is there no article before Kaffee? Why not Ich trinke seltener den Kaffee?

In German, when you talk about something in general (not a specific coffee), you normally use a bare noun without an article:

Ich trinke Kaffee. = I drink coffee (in general).
Ich trinke seltener Kaffee. = I drink coffee less often (in general).

If you say den Kaffee, you point to a specific coffee, for example:

Ich trinke den Kaffee nicht, weil er kalt ist.
= I’m not drinking this coffee, because it’s cold.

So in your sentence, the general meaning is intended, so no article.

What exactly does seltener mean here? Is it “less coffee” or “less often”?

Seltener is the comparative of selten = “rarely, seldom”.

selten = rarely
seltener = more rarely, less often

So:

Ich trinke seltener Kaffee.
= I drink coffee less often (not as frequently as before).

If you wanted to say that you drink a smaller amount of coffee (quantity), you’d use weniger:

Ich trinke weniger Kaffee.
= I drink less coffee (a smaller amount).

Your sentence focuses on frequency, not volume.

Why is it seltener Kaffee and not selteneren Kaffee?

Here seltener is not an adjective describing the noun Kaffee. It’s an adverb describing the verb trinke (“drink less often”).

So the structure is:

Ich trinke [seltener] [Kaffee].
= I drink coffee less often.

If you were using seltener as an adjective directly with a noun, you would need endings:

ein seltener Kaffee = a rare coffee (unusual kind)
einen selteneren Kaffee = a rarer coffee

But that would change the meaning completely. In your sentence, seltener modifies the action (how often you drink), not the coffee itself.

Can I also say Ich trinke Kaffee seltener? Is that the same?

Yes, Ich trinke Kaffee seltener is grammatically correct and means almost the same thing.

Word order nuances:

Ich trinke seltener Kaffee.
Slightly more neutral; frequent way to say “I drink coffee less often.”
Ich trinke Kaffee seltener.
Also fine; some speakers might feel a tiny emphasis on Kaffee (compared with other drinks), but in everyday usage the difference is minimal.

Both are good and natural; the original version is very common.

What does sonst mean in this sentence? Is it “otherwise”?

Yes, sonst here means “otherwise” / “or else”.

Your sentence:

…, weil ich sonst schlecht schlafe.
= “…because otherwise I sleep badly.”

So the logic is:

I drink coffee less often,
because if I don’t do that, otherwise I’ll sleep badly.

In such causal sentences, sonst often expresses a negative consequence that would happen if you didn’t do the action in the main clause.

Could I use denn instead of weil?

You can, but the sentence structure changes.

With weil (subordinate clause → verb at the end):
Ich trinke seltener Kaffee, weil ich sonst schlecht schlafe.
With denn (coordinating conjunction → normal word order):
Ich trinke seltener Kaffee, denn ich schlafe sonst schlecht.

Both are grammatically correct. Differences:

weil usually sounds a bit more conversational and directly causal.
denn is often used more in written style or slightly formal speech.

Meaning is basically the same.

Why is it schlecht schlafe and not schlafe schlecht?

Because you’re in a subordinate clause introduced by weil. In such clauses, the finite verb goes to the end, and everything else (subject, objects, adverbs) goes before it:

Main clause: Ich schlafe schlecht. → Verb in 2nd position
Subordinate clause: …, weil ich schlecht schlafe. → Verb at the end

So:

✅ …, weil ich sonst schlecht schlafe.
As a main clause: ✅ Ich schlafe sonst schlecht.

Is schlecht schlafen a fixed expression? Could I say nicht gut schlafe instead of schlecht schlafe?

Schlecht schlafen is very common and idiomatic: to sleep badly / to sleep poorly.

You can say:

…, weil ich sonst nicht gut schlafe.
= “…because otherwise I don’t sleep well.”

Both schlecht schlafen and nicht gut schlafen are natural.
Schlecht schlafen is a bit shorter and a very typical phrase.

Why is the sentence in the present tense? In English I might say “I drink less coffee because otherwise I will sleep badly.”

German often uses the present tense where English would use the future. The context makes it clear that it’s about a general or future consequence.

Your sentence:

Ich trinke seltener Kaffee, weil ich sonst schlecht schlafe.
= Literally: “I drink coffee less often, because otherwise I sleep badly.”

English often prefers “will sleep” here, but in German present tense is completely natural for:

general truths
habits
expected future outcomes

You could say …, weil ich sonst schlecht schlafen werde, but that sounds more formal and is rarely needed in everyday speech.

Could I say Ich trinke selten Kaffee instead of Ich trinke seltener Kaffee?

Yes, but the meaning changes slightly:

Ich trinke selten Kaffee.
= I rarely drink coffee. (In general, it doesn’t happen often.)
Ich trinke seltener Kaffee.
= I drink coffee less often (than before / than usual / than others).

Selten describes a general low frequency.
Seltener is a comparative: “less often (than X)”.
Often the comparison (than before) is just implied by context.

Could this sentence start with weil? For example: Weil ich sonst schlecht schlafe, trinke ich seltener Kaffee.

Yes, that’s perfectly correct and common:

Weil ich sonst schlecht schlafe, trinke ich seltener Kaffee.

When a subordinate clause comes first:

The subordinate clause keeps the verb at the end: …, schlafe.
The main clause that follows still has the verb in 2nd position, so the subject and verb are inverted:
- not: ❌ …, ich trinke seltener Kaffee.
- but: ✅ …, trinke ich seltener Kaffee.

Both orders are natural:

Ich trinke seltener Kaffee, weil ich sonst schlecht schlafe.
Weil ich sonst schlecht schlafe, trinke ich seltener Kaffee.