When the pronoun _het_ is preceded by a preposition, we replace _het_ by _er_ (see also [het turning into er](#/lesson/Pronouns.Ps09)). The same goes for _ze_ (them) and _hem_ if they refer to something inanimate.
Not only is the pronoun replaced by _er_, the preposition is also attached to _er_. Moreover, it does not precede it - as it does with a noun, but it is placed after it. The preposition, thus, turns into a postposition.
We do not say: "Ik hoop op het", but: "Ik hoop erop". Following the same rule, _in het_ becomes _erin_, _over het_ becomes _erover_, et cetera. Recall that this only applies to _het_ functioning as a pronoun, not to the [article](#/lesson/NounsAndArticles.01) _het_!
For _de zeep_ (the soap), we normally use the pronoun _hem_.
Ik heb mijn handen met zeep gewassen | I have washed my hands with soap
Ik heb er mijn handen mee gewassen | I have washed my hands with it
We do not say: "Ik heb mijn handen _met hem_ gewassen."
Normally, prepositions stay the same if we turn them into postpositions. The prepositions _met_ (with) and _tot_ (to, until) are exceptions: They turn into _mee_ and _toe_ respectively. For example: _Tot het_ becomes _ertoe_ en _met het_ becomes _ermee_.
Just like _de zeep, de paraplu_ is a _de_-noun: We would use the pronoun _hem_.
Ik heb onder een paraplu gelopen | I have walked under an umbrella
Ik heb eronder gelopen | I have walked under it
We do not say: "Ik heb _onder hem_ gelopen".
For _het hek_ we normally use the pronoun _het_.
De bal werd over het hek heen\\* gegooid. | The ball was thrown over the fence
De bal werd eroverheen gegooid | The ball was thrown over it
We do not say: "De bal werd _over het_ gegooid".
(\*) _Heen_ is a postposition that often occurs with a preposition indicating movement, in this example with _over_
For the plural noun _hoge hakken_ (high heels), we normally use the pronoun _ze_.
Ze loopt op hoge hakken. | She walks on high heels.
Ze loopt erop. | She walks on them.
We do not say: "Ze loopt _op ze_."
Note that _deze/dit_ (this) and _die/dat_ (that) are replaced by _hier_ and _daar_ in the same way (see also [dit/dat turning into hier/daar](#/lesson/Pronouns.De04)).