Questions & Answers about Mi ne kredas tiun mensogon.
Because tiun mensogon is the direct object of kredas.
In Esperanto, the direct object usually takes the accusative ending -n. Words that go together also agree with each other, so:
- tiu mensogo = that lie
- tiun mensogon = that lie (as a direct object)
Here, the speaker is not believing that lie, so that lie is the thing being acted on by the verb kredas.
Tiu is the basic form meaning that one / that.
When it modifies a noun and the whole noun phrase is a direct object, it changes to tiun to match the accusative:
- tiu mensogo = that lie
- tiun mensogon = that lie (object form)
So tiun is not a different word; it is just tiu with the object ending -n.
For the same reason: mensogo is the noun, and as a direct object it takes -n.
- mensogo = a lie / lie
- mensogon = a lie / lie as the direct object
Since the sentence is about not believing the lie, is the object of .