The relative pronoun wat after alles, iets, a superlative, or a whole clause

Both Alles wat klaar is and Alles dat klaar is mean ‘Everything that is ready’, so Dutch does not always force a choice between relative wat and dat. A complete preceding statement requires wat: in De levering kwam te laat, wat extra kosten veroorzaakte. (The delivery arrived late, which caused extra costs.), wat comments on the whole event.

After an indefinite pronoun or a nominalised adjective, wat is a standard option alongside dat. After a whole preceding clause, use wat, not dat. First identify what the relative clause refers back to.

1. After alles, iets, niets, and similar indefinite forms, both wat and dat are correct: Er is iets wat/dat we moeten bespreken. (There is something that we need to discuss.)
2. After het enige and a nominalised adjective or superlative, both forms are possible: Dat is het verstandigste wat/dat je nu kunt doen. (That is the wisest thing you can do now.)
3. After a complete clause or thought, use a comma plus wat: De afspraak werd geannuleerd, wat niemand had verwacht. (The appointment was cancelled, which nobody had expected.)

With indefinite forms, wat is often common and may sound more natural, especially after alles. That preference does not make alles dat wrong. The same applies to het enige dat: it is standard Dutch, just like het enige wat.

Sometimes. Relative wat can give the superlative a broad domain: all relevant things or experiences. Relative dat can recover an unspoken singular neuter noun and compare members of that noun class. This is a meaning nuance, not a claim that either form is generally incorrect.

Context can reduce or remove the difference, so do not force two readings into every sentence. The contrast is clearest when dat has an obvious neuter noun to recover and the broader set for wat is plausible.

A complete statement can act as the antecedent of a non-restrictive relative clause. Put a comma before wat: De commissie stelde het besluit uit, wat tot nieuwe vragen leidde. (The committee postponed the decision, which led to new questions.). Here wat refers to the postponement, not just to het besluit.

If the relative clause needs a preposition, replace preposition + wat with a relative waar-form: Het loket sloot vroeg, waar veel bezoekers niet op hadden gerekend. (The desk closed early, which many visitors had not expected.). The verb frame is op iets rekenen, so the clause uses waar ... op.

The noun-building patterns datgene wat and formal hetgeen belong to relatives without a separate noun. This page only cross-links them; it does not use them to redefine the choices above.

• Use wat or dat after an indefinite form: alles wat/dat, iets wat/dat, and niets wat/dat.
• Use wat or dat after het enige and nominalised adjectives or superlatives.
• Choose wat for a broad superlative reading and dat when you intend a recoverable neuter noun, if the context makes that contrast relevant.
• Use comma + wat when the antecedent is a whole preceding clause.
• Use waar + preposition when the relative role includes a preposition: waar ... mee, waar ... op, or another appropriate combination.

• Do not mark alles dat or het enige dat as an error; both have standard alternatives with wat.
• Do not use dat to comment on a whole preceding clause: write De prijs daalde, wat ons verbaasde.
• Do not confuse a noun antecedent with a clause antecedent: het bericht dat ... modifies bericht, while comma + wat can refer to the whole event.
• Do not place wat directly after a preposition in this pattern; use a waar-form where Dutch permits one.

Review ordinary relative die and dat, relative clauses with a preposition, and indefinite people and things. Keep relative wat separate from indirect-question order.