Placing the direct object: definite vs indefinite

The direct object is the thing the action is done to: in Ik heb de brief gepost (I posted the letter), de brief is the direct object. In the middle of a Dutch main clause it has no single fixed spot. Where it lands depends on whether it is definite (something already known — de brief, the letter) or indefinite (something new — een brief, a letter): Ik heb de brief vanmorgen gepost but Ik heb vanmorgen een brief gepost.

A definite object sits early in the middle field, before adverbs of time, manner and place; an indefinite object sits late, just before the verbs at the end of the clause.

1. Decide whether the object is definite or indefinite (the next section lists what counts).
2. Definite → place it right after the front block (subject + finite verb), before any time/manner/place words: Ze heeft de auto gisteren gewassen. (She washed the car yesterday.)
3. Indefinite → place it after the time/manner/place words, next to the final verb(s): Ze heeft gisteren een auto gewassen. (She washed a car yesterday.)

A definite object may also move to the end for emphasis (Ze heeft gisteren de auto gewassen stresses which car), but the early position is the neutral one. An indefinite object has no such freedom — it stays at the end.

Definiteness here is about the words that open the object, not the meaning you feel.

• Definite: starts with de or het (het boek), a possessive (mijn fiets, my bike), a demonstrative (deze, die, dit, dat), or is a proper name (Ik heb Anna gebeld — I called Anna).
• Indefinite: starts with een (een boek), has no article because it is a bare plural (Ik koop appels — I buy apples), starts with a number (vier appels), or with an indefinite word like geen (no), veel (much/many) or wat (some).
• A personal pronoun object (het, hem, ze) counts as definite, but it goes even further forward, hugging the finite verb — see where object pronouns sit.

Because a definite object sits early, whole-sentence niet comes after it: Ik heb de film niet gezien. (I didn't see the film.) An indefinite object is normally negated with geen, not niet + een: Ik heb geen film gezien. (I didn't see a/any film.) The choice between niet and geen is covered under niet or geen and where niet goes.

English keeps the object right after the verb (I posted a letter this morning), so learners copy that order and write Ik heb een brief vanmorgen gepost. In Dutch an indefinite object cannot stand before the time word — it must go to the end: Ik heb vanmorgen een brief gepost. Move the een-object (or a bare plural or a number) to just before the final verb and the sentence comes right.