erop, ermee, eraan: er + a preposition

In Dutch you cannot put a preposition in front of the thing-pronoun het (it) or ze (them). Instead, the pronoun becomes er and the preposition hooks onto the back of it: op het → erop (on it), met het → ermee (with it), aan het → eraan (about/on it). Waar wacht je op? — Ik wacht erop. (What are you waiting for? — I'm waiting for it.) Grammar books call this an er + preposition combination a pronominal adverb.

Take the preposition that belongs to the verb and glue it after er as one word: er + preposition. It replaces preposition + it/them whenever that 'it' is a thing, not a person.

1. Find the preposition: denken aan (to think about), wachten op (to wait for), houden van (to like).
2. Attach it to er: eraan, erop, ervan. Ik hou van deze stad → Ik hou ervan. (I like it.)
3. Two prepositions change shape here: met becomes mee → ermee (with it), and tot becomes toe → ertoe (to it).

This trick is only for things. When the object is a person, keep the ordinary preposition + object pronoun: Ik wacht op hem (I'm waiting for him), not ik wacht erop in that sense. For people after a preposition, Dutch uses hem/haar/hen; for things it uses er.

Very often er and its preposition are pulled apart, with other words wedged between them. The er moves forward in the sentence and the preposition drops back toward the end, just before any final verbs.

• Add a word like niet or nog and the pair splits: Ik reken erop → Ik reken er niet op. (I'm not counting on it.)
• A time word splits it too: Ik heb er lang op gewacht. (I waited for it a long time.)
• In a longer clause the preposition lands right before the verb at the end: Ik heb er nog nooit over nagedacht. (I have never thought about it.)

• After a verb locked to a fixed preposition, when the object is a thing you have already mentioned: wachten op → erop, denken aan → eraan, zoeken naar → ernaar.
• To answer or continue about a thing without repeating the noun: Wat vind je van de film? — Ik vind er niets aan. (What do you think of the film? — I don't like it.)
• The question and relative versions work the same way with waar: waarop, waarmee, waarover (see waarmee, waarover).

Learners try to translate with it word-for-word as met het and on it as op het. Dutch does not allow a preposition before het here — say ermee and erop. The second common slip is forgetting to split: once you add another word, er and the preposition come apart. Ik denk eraan niet is wrong; it is Ik denk er niet aan.