Learn Hardcore German: Unbekannte Wörter schlage ich sofort im Onlinelexikon nach, damit ich meinen Wortschatz aktiv erweitere. - Unknown words I look up immediately in the online dictionary so that I actively expand my vocabulary.

German main clauses follow a verb-second (V2) rule: the conjugated verb must be in second position, but almost anything can be in first position.

Neutral order:
- Ich schlage unbekannte Wörter sofort im Onlinelexikon nach.
With the object in first position (for emphasis / topic):
- Unbekannte Wörter schlage ich sofort im Onlinelexikon nach.

By putting Unbekannte Wörter first, the speaker emphasizes what they look up, rather than who is doing it. It’s a stylistic choice, not a grammatical necessity. Both versions are correct.

What does schlage ... nach mean? Why is the verb split?

nachschlagen is a separable verb in German. Its basic meaning here is “to look up (in a dictionary / reference work)”.

In the infinitive form:

nachschlagen = to look up

In a main clause in the present tense, separable verbs split:

The conjugated part goes in second position.
The separable prefix goes to the end of the clause.

So:

ich schlage nach = I look up
In the sentence: Unbekannte Wörter schlage ich sofort im Onlinelexikon nach.

Other examples:

Ich stehe früh auf. (aufstehen – to get up)
Wir machen das Licht an. (anmachen – to turn on)

So schlage ... nach is just the normal present-tense main-clause form of nachschlagen.

Why is it im Onlinelexikon and not in dem Onlinelexikon?

im is a contraction of in dem:

in dem Onlinelexikon → im Onlinelexikon

German very often contracts in dem → im, just like English often contracts “do not → don’t”.

You could technically say in dem Onlinelexikon, and it would be grammatically correct, but in everyday language im is much more natural.

What case is Onlinelexikon in, and why?

Onlinelexikon is in the dative case.

Reason: the preposition in can take either accusative or dative:

in + accusative = movement into something (direction)
in + dative = location in something (no movement)

Here, the meaning is “in the online dictionary” as a location, so we use dative:

in dem Onlinelexikon → dative singular → contracted to im Onlinelexikon

Why is Unbekannte capitalized? Isn’t that just an adjective?

It looks like just an adjective, but two things are happening here:

The sentence starts with Unbekannte, so the first letter must be capitalized anyway.
More importantly, the full phrase is Unbekannte Wörter:
- Wörter is a noun and must be capitalized.
- unbekannte is an adjective and normally written in lower case:
  unbekannte Wörter = unknown words

If you wrote it in the middle of a sentence, it would be:

Ich schlage unbekannte Wörter sofort im Onlinelexikon nach.

So the capitalization here comes from:

First word of the sentence: U must be capital.
The noun Wörter is also capitalized, as all German nouns are.

Only the noun Wörter is inherently capital; unbekannte is just capitalized because it’s at the start of the sentence.

Why is it Unbekannte Wörter and not Unbekannten Wörter? How do the endings work?

This is about adjective endings.

Wörter is:

plural
nominative case
no article before it

In that situation (plural, no article, nominative), the adjective takes -e:

unbekannte Wörter
alte Bücher
teure Autos

If there were a definite article, the ending would change:

die unbekannten Wörter (plural nominative with article die → adjective gets -en)

So:

Unbekannte Wörter (no article, plural, nominative) → -e
die unbekannten Wörter (with definite article, plural, nominative) → -en

What exactly does sofort mean, and why is it placed there?

sofort means “immediately / right away”.

In terms of word order:

Commonly, time adverbs like sofort appear before the place or manner phrase but after the verb (or close to it).

The part schlage ich sofort im Onlinelexikon nach is perfectly natural:

sofort (when? → immediately)
im Onlinelexikon (where? → in the online dictionary)

Other possible (still correct) positions:

Ich schlage unbekannte Wörter sofort im Onlinelexikon nach.
Ich schlage unbekannte Wörter im Onlinelexikon sofort nach. (less common, slightly marked)

The chosen position schlage ich sofort im Onlinelexikon nach is idiomatic and clear.

What is the role of damit here? How is it different from um ... zu?

damit introduces a purpose clause (“so that / in order that”).

In the sentence:

..., damit ich meinen Wortschatz aktiv erweitere.
= “... so that I actively expand my vocabulary.”

Key points:

damit is a subordinating conjunction:
- It sends the conjugated verb to the end of the clause:
  - ich erweitere → damit ich ... erweitere
Difference from um ... zu:
- um ... zu is used when the subject is the same in both clauses:
  - Ich schlage unbekannte Wörter nach, um meinen Wortschatz aktiv zu erweitern.
- damit can be used when the subject is different, but it’s also acceptable when the subject is the same, as here:
  - ..., damit ich meinen Wortschatz aktiv erweitere.

So with this sentence, you could also say:

Unbekannte Wörter schlage ich sofort im Onlinelexikon nach, um meinen Wortschatz aktiv zu erweitern.

Both are correct; damit feels a bit more like a full finite clause (“so that I ...”).

Why is the verb erweitere at the very end of the clause?

Because it’s in a subordinate clause introduced by damit.

In German:

Main clause: conjugated verb usually in second position.
Subordinate clause (with words like dass, weil, wenn, damit): conjugated verb goes to the end.

So:

Main clause: Ich erweitere meinen Wortschatz.
Subordinate with damit:
..., damit ich meinen Wortschatz aktiv erweitere.

This verb-final position is standard for subordinate clauses in German.

Why is it meinen Wortschatz (accusative) and not mein Wortschatz?

meinen Wortschatz is in the accusative case, because it is the direct object of the verb erweitern (to expand).

Subject: ich (I)
Verb: erweitere (expand)
Direct object: meinen Wortschatz (my vocabulary)

For masculine nouns like Wortschatz (der Wortschatz):

Nominative: mein Wortschatz
Accusative: meinen Wortschatz

Since the vocabulary is what is being expanded, it must be in the accusative:

Ich erweitere meinen Wortschatz.

What is the nuance of aktiv erweitere? Why is aktiv placed before the verb?

aktiv here is an adverb meaning “actively, in an active way / deliberately”.

meinen Wortschatz erweitern = to expand my vocabulary
meinen Wortschatz aktiv erweitern = to actively expand my vocabulary, as opposed to just passively picking up words.

Placing aktiv before the verb is normal adverb placement in German:

Ich lerne aktiv.
Ich höre aktiv zu.
damit ich meinen Wortschatz aktiv erweitere.

You could also put it slightly differently (e.g. aktiv meinen Wortschatz erweitere), but meinen Wortschatz aktiv erweitere is smooth and common: object first, then the adverb modifying the action.

Is there any difference between Wörter and Worte? Why is Wörter used here?

Yes, there is a difference, even though both are plural of Wort.

Rough rule of thumb:

Wörter = individual, countable words, especially as vocabulary items.
- 20 neue Wörter lernen – to learn 20 new words
Worte = words as part of an utterance or expression, more “connected speech” or “famous words”.
- Seine letzten Worte waren ... – his last words were ...
- in anderen Worten – in other words

Here we’re talking about vocabulary items that you might look up in a dictionary, so Wörter is correct:

Unbekannte Wörter schlage ich ... nach.
= Unknown vocabulary items, not “utterances” or “sayings”.