Learn Hardcore German: Es ist klug, den Antrag früh zu schicken, auch wenn das Problem ernst wirkt. - It is smart to send the application early, even if the problem seems serious.

It’s a dummy subject (an anticipatory es). The real content subject is the zu-infinitive clause den Antrag früh zu schicken. German often avoids a heavy clause in subject position by using Es up front: Es ist klug, …. You could also say Den Antrag früh zu schicken ist klug, but the version with Es sounds lighter and more neutral.

Why is it zu schicken and not just schicken?

After expressions like Es ist + adjective (here: Es ist klug), German typically uses a zu-infinitive to express what is being evaluated: Es ist klug, den Antrag früh zu schicken. A bare infinitive here is ungrammatical. An alternative would be a dass-clause: Es ist klug, dass man den Antrag früh schickt, but the zu-infinitive is more idiomatic and concise.

What’s the purpose of the commas?

The comma after klug sets off the zu-infinitive group (den Antrag früh zu schicken). In modern German it’s standard (and strongly recommended) to use a comma to separate an expanded zu-infinitive group like this.
The comma before auch wenn is mandatory because auch wenn … wirkt is a subordinate clause that must be set off by a comma.

Why is it den Antrag and not dem Antrag or einen Antrag?

den is accusative singular masculine. schicken takes a direct object in the accusative, and Antrag is masculine (der Antrag → den Antrag).
den Antrag (definite) implies a specific application known to speaker/hearer. einen Antrag would be indefinite/generic: It’s wise to send an application early (not a specific one).
dem Antrag would be dative and is wrong here because there’s no dative slot without a recipient (e.g., jemandem den Antrag schicken).

Is Antrag the right word? What about Bewerbung or Anfrage?

der Antrag = a formal request/application submitted to an authority (e.g., visa, grant, permit).
die Bewerbung = job/university application.
die Anfrage = inquiry/question/request for information. So if you mean a formal submission to an office, Antrag is appropriate.

Is schicken the best verb here? I’ve seen einreichen, stellen, abschicken.

einen Antrag einreichen = to submit an application (very common and formal/official).
einen Antrag stellen = to file an application (very common formula).
(ab)schicken = to send (physically or via email). This is fine if the act is literally sending, but for official contexts einreichen/stellen often sounds more idiomatic. With a separable verb you’d say: … frühzeitig einzureichen / früh abzuschicken.

Why is früh used? Could I say frühzeitig, zeitig, or bald?

früh = early (plain and neutral).
frühzeitig = early/in good time (preferred in formal/administrative contexts: den Antrag frühzeitig einreichen is very idiomatic).
zeitig = early/in time (colloquial/regional flavor).
bald = soon (not necessarily early relative to a deadline). All are possible depending on tone; for official advice, frühzeitig einreichen is very natural.

Is the word order inside the zu-clause fixed? Why den Antrag früh zu schicken and not früh den Antrag zu schicken?

Both are grammatical, but den Antrag früh zu schicken is the more neutral, natural order. früh den Antrag zu schicken front-loads the time adverb and can add emphasis to “early.” In everyday style, object-before-adverb here feels smoother.

How do I form zu-infinitives with separable verbs like abschicken and einreichen?

Insert zu between the prefix and the verb stem:

abschicken → abzuschicken
einreichen → einzureichen So: Es ist klug, den Antrag früh abzuschicken / frühzeitig einzureichen.

Why wirkt and not ist? What about scheint?

wirken means “to appear/seem” in the sense of giving an impression: Das Problem wirkt ernst = It comes across as serious.
sein states a fact: Das Problem ist ernst.
scheinen also means “seem.” With adjectives, both Das Problem scheint ernst and Das Problem scheint ernst zu sein are used; the version with zu sein is a bit more formal/explicit.
Here wirkt highlights perceived seriousness rather than asserting it as a fact.

What’s the difference between auch wenn and obwohl (and selbst wenn)?

obwohl = although/even though (concedes a fact).
auch wenn = even if/even though (often a bit more concessive and can be hypothetical).
selbst wenn = even if (strongly hypothetical). In your sentence, auch wenn and obwohl are both fine:
…, auch wenn das Problem ernst wirkt.
…, obwohl das Problem ernst wirkt. If you want a clearly hypothetical nuance, use selbst wenn.

Why is the verb at the end of auch wenn das Problem ernst wirkt?

Because auch wenn introduces a subordinate clause, and in German subordinate clauses send the finite verb to the end: … das Problem ernst wirkt. In main clauses, the verb is in second position.

Why is it ernst and not ernste?

After linking verbs like sein, werden, bleiben, wirken, adjectives are used predicatively and do not take endings: Das Problem ist/bleibt/wirkt ernst. By contrast, attributive adjectives before nouns take endings: ein ernstes Problem, das ernste Problem.

Why are Antrag and Problem capitalized?

All nouns are capitalized in German: der Antrag, das Problem. Adjectives and adverbs like ernst and früh are not capitalized (unless they start a sentence or are part of a proper noun).

Could I say Es wäre klug, … instead of Es ist klug, …?

Yes. Es wäre klug, … (It would be wise) is a softer, more advisory tone. Es ist klug, … (It is wise) sounds more definite/general.

Can I front the auch wenn clause? Does the meaning change?

You can front it with no change in meaning: Auch wenn das Problem ernst wirkt, ist es klug, den Antrag früh zu schicken. This is common and perfectly natural; just keep the commas and verb-final order in the subordinate clause.

Can I drop Es and make the zu-clause the subject?

Yes: Den Antrag früh zu schicken ist klug. This is grammatical and emphasizes the action itself. The version with Es is stylistically smoother in many contexts.

Should I ever use the subjunctive here (e.g., wirke or würde wirken)?

Normally no. wirkt (indicative) is standard.

wirke (Konjunktiv I/II) would sound stilted or like reported speech.
würde wirken is possible in a clearly hypothetical reading (… selbst wenn das Problem ernst wirken würde), but it isn’t necessary for your sentence.

Is there any difference between früh and rechtzeitig here?

früh = early (before the usual or expected time).
rechtzeitig = in good time/by the deadline (timely).
If you mean “don’t wait until it’s too late,” rechtzeitig or frühzeitig often fits official contexts well: den Antrag rechtzeitig/frühzeitig einreichen.