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Ich weiß nicht, welches Buch ich heute lesen soll.

Ich weiß nicht, welches Buch ich heute lesen soll.
I don't know which book I should read today.
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Questions & Answers about Ich weiß nicht, welches Buch ich heute lesen soll.

Why is it welches Buch and not something like welcher Buch or welche Buch?

German determiners (like welch-) have to agree with the noun in gender, number, and case.

  • Buch is neuter (das Buch).
  • In this sentence, welches Buch is the direct object of lesen → that is accusative case.
  • For a neuter, singular, accusative noun, welch- takes the ending -es: welches Buch.

Small pattern for welch- with neuter nouns:

  • Nominative singular: welches Buch (Which book is on the table?)
  • Accusative singular: welches Buch (Which book should I read?) So nominative and accusative look the same for neuter. Here it’s accusative because it is what you read.
What case is welches Buch in, and how can I tell?

Welches Buch is in the accusative case.

You can tell because:

  • The verb is lesen (to read).
  • In ich … lesen soll, the thing being read is the direct object → that’s accusative.
  • The form welches (not welchem) tells you it’s not dative; for neuter, nominative and accusative are identical: welches.

So the internal structure of the clause is:

  • ich → subject (nominative)
  • welches Buch → direct object (accusative)
  • lesen → main verb
  • soll → modal verb.
Why is Buch capitalized?

In German, all nouns are capitalized, regardless of position in the sentence.

Buch (book) is a noun, so it’s written with a capital B:

  • das Buch
  • ein interessantes Buch
  • welches Buch

This is just a standard spelling rule in German, not a special case.

Why is there a comma before welches?

The comma marks the start of a subordinate clause (a dependent clause).

  • Ich weiß nicht = main clause.
  • welches Buch ich heute lesen soll = subordinate clause that functions like the object of weiß.

In German, you must put a comma before a subordinate clause introduced by a question word (welches, was, warum, wie, etc.). So the comma is obligatory here.

Why does the verb go to the end in welches Buch ich heute lesen soll?

In German subordinate clauses, the finite verb (the conjugated verb) normally goes to the end of the clause.

Here:

  • Main clause: Ich weiß nicht → normal word order (verb in position 2).
  • Subordinate clause: welches Buch ich heute lesen soll
    • ich = subject
    • heute = time adverb
    • lesen = infinitive
    • soll = finite modal verb → goes at the very end.

So:

  • Main clauses: Ich lese heute ein Buch. (verb in 2nd position)
  • Subordinate clauses: …, dass ich heute ein Buch lese. (verb at the end)

With a modal + infinitive in a subordinate clause, the order is: … lesen soll, not … soll lesen.

Why is it lesen soll and not soll lesen at the end?

In a subordinate clause, the rule with modal verbs is:

Infinitive + finite modal verb at the end.

So you get:

  • … welches Buch ich heute lesen soll.

If this were a main clause, you would say:

  • Ich soll heute ein Buch lesen. (finite verb in 2nd position, infinitive at the end)

Compare:

  • Main clause: Ich soll das Buch lesen.
  • Subordinate clause: …, dass ich das Buch lesen soll.

So lesen soll is exactly what the grammar of subordinate clauses requires.

Why do we use soll here instead of muss or kann?

The verb sollen often corresponds to English “should” or “be supposed to”, while:

  • müssen = must / have to (strong obligation, necessity)
  • können = can / be able to (ability or possibility)

In this sentence:

  • Ich weiß nicht, welches Buch ich heute lesen soll.
    → I don’t know which book I should read today / which book I’m supposed to read today.

So soll expresses:

  • A recommendation: which one would be the right/best choice to read.
  • Or a task/assignment: which one I’m expected to read (e.g. for school).

Muss would sound like you are forced to read a book:

  • welches Buch ich heute lesen muss = which book I have to read today.

Kann would mean you are talking about what is possible for you to read:

  • welches Buch ich heute lesen kann = which book I can read today.
Why is the negation nicht placed after weiß and not after ich?

In German, nicht usually comes after the conjugated verb when you negate the whole statement.

  • Ich weiß nicht … = I do not know …
  • Putting nicht after ich (Ich nicht weiß …) is incorrect word order in standard German.

Some patterns:

  • Ich verstehe nicht. (I don’t understand.)
  • Ich glaube nicht, dass … (I don’t believe that …)
  • Ich weiß nicht, welches Buch … (I don’t know which book …)

So Ich weiß nicht is a fixed and very common pattern.

Why is it wissen (ich weiß) and not kennen in this sentence?

German distinguishes between:

  • wissen = to know a fact, information, answer, clause (that, which, when, etc.)
  • kennen = to know a person, place, or thing (to be familiar with it)

Here, what you do not know is a piece of information: which book to read.

So you must use wissen:

  • Ich weiß nicht, welches Buch ich heute lesen soll.

Examples:

  • Ich weiß nicht, wie spät es ist. (fact)
  • Ich kenne dieses Buch nicht. (I’m not familiar with this book, haven’t read it, etc.)
Why is it written weiß with ß and not weis or weiss?

The infinitive is wissen, but the first person singular is ich weiß.

  • Historically, the ß (Eszett) represents a voiceless “s” sound after a long vowel or diphthong.
  • In weiß, the vowel is long, so spelling rules give you ß.

Conjugation of wissen (present tense):

  • ich weiß
  • du weißt
  • er/sie/es weiß
  • wir wissen
  • ihr wisst
  • sie/Sie wissen

In Germany, weiß with ß is the standard spelling. In Switzerland, weiss is often used instead (they don’t use ß), but in most German-learning contexts weiß is what you’ll see.

Why is heute in the middle (ich heute lesen soll) and not at the end?

Adverbs of time like heute are quite flexible, but in a subordinate clause the typical neutral position is after the subject and before the main verb phrase:

  • welches Buch ich heute lesen soll

This mirrors a very common main-clause order:

  • Ich lese heute das Buch. (subject – verb – time – object)

Other positions are possible, but they may sound more marked or emphasize the time:

  • welches Buch ich lesen soll heute → grammatical but sounds a bit unusual or colloquial/emphatic.
  • welches Buch ich morgen lesen soll → same pattern with a different time word.

The given sentence uses the most natural, neutral-sounding placement.

Can I move heute to the end and say … welches Buch ich lesen soll heute?

Yes, it is grammatically possible:

  • Ich weiß nicht, welches Buch ich lesen soll heute.

However:

  • It sounds more colloquial and less neutral.
  • The normal, most idiomatic order is still:
    • …, welches Buch ich heute lesen soll.

So you might hear or say the version with heute at the end in spoken, informal German, but for learning and for writing, it’s better to stick to ich heute lesen soll.

Could I also say Ich weiß nicht, was für ein Buch ich heute lesen soll? What’s the difference from welches Buch?

Yes, you can say:

  • Ich weiß nicht, was für ein Buch ich heute lesen soll.

The nuance is slightly different:

  • welches Buch
    → You are choosing from a specific, known set of books (e.g. the ones on your shelf or a reading list).
    → Literally: which book (of these).

  • was für ein Buch
    → More about the type or kind of book (e.g. thriller, novel, non-fiction), or a less clearly defined set.
    → Literally: what kind of book.

In practice, context decides how big the difference feels, but welches Buch strongly implies you have concrete options in mind.