I am having trouble figuring out which form of lavi to use, either lavis or laviĝis. Here is what I am trying to say:
Mi manĝis la pomon ke ne laviĝis.
I ate the apple that was not washed (i.e. cleaned).
Did I write that sentence correctly? In what situations do I use lavi and laviĝis?
Mi manĝis la pomon ke ne laviĝis.
The first thing that jumps out is that the word in the middle needs to be kiu. Ke is a conjunction that is used to join complete sentences. If you're translating "that" or "which" and it's the subject of the phrase, then you probably need kiu or another correlative.
The one detail that I would add to Kristan's answer is that laviĝis often has the connotation of something just sort of happening without an agent.
If there's someone who was supposed to wash the apple and it didn't happen (as in the case you described) I would use a more active construction.
You want "kiu" rather than "ke" there; "Mi manĝis la pomon kiu...". (If you can replace "that" with "which" in the sentence and have it make sense, use "kiu(n)").
The word "lavi" means "to wash", so "Mi manĝis la pomon kiu ne lavis" means "I ate the apple that didn't wash". So you could say "Mi manĝis la pomon kiu ne laviĝis", meaning "I ate the apple that didn't get washed".
Another option is to use "-ita"; "Mi manĝis la pomon kiu ne estis lavita", or more simply "Mi manĝis la nelavitan pomon", meaning "I ate the unwashed apple".
You need to use the word kiu instead of ke. Kiu describes what kind of apple it is.
I ate the apple, which was not washed = Mi manĝis la pomon, kiu ne laviĝis.
