あります means: to have / to be
Both sentences have the same meaning I guess.
Could someone explain me both sentences and how the conjugation works?
Until now I only knew about:
polite vs informal
Example 1 is the polite way to say it (adding -ありませんでした) , example 2 is the informal way (adding -なかった)
But yes, they’re both saying the same thing 
I think this part is what confuses me.
If I do this sentence
with です it would be
Why does the 面白 looses the なかった part in sentence nr.1?
The only difference here is the conjugation of ある in the past negative, polite vs. casual.
The casual conjugation of ある in past negative is なかった. In polite conjugation it’s ありませんでした. The casual one has です tacked onto the end to make it polite as well.
The first sentence is polite, as you might know. ありませんでした is the negative form of ありました、which again is a formal version of ある. The negative form of ある, ない, ends in い, and is conjugated just like an adjective. That’s how we end up with なかった.
面白く is an adverb that affects the verb it follows, so it’s actually ありませんでした that gets modified, not the other way around.
面白い is an adjective
I mixed a lot of things together. I need to read over this again.
Of course, 面白い is an adjective, but 面白く is an adverb. Replacing the い in an adjective with くturns it into an adverb.
wow, you solved the knot in my head. 
I thought that く was part of some conjugation because of ‘く’ なかった
Could it be that you only conjugate the last word of the sentence?
It’s not really the case that you conjugate the last word of the sentence. It would depend on context.
隣人がボールを投げたのを見た (I saw the neighbour throwing a ball) is an example where you would need to conjugate several verbs in the same sentence.
隣人が「大きい」ボールを投げたのを見た。
But if I would add that the ball is big. would I need to conjugate the 「大きい」adjective?
or:
In which case do I need to conjugate adjectives?
Could it be like that:
if the focus of the sentence is on the adjective like.
私のボールは大きかったです。
I need to conjugate it.
But if its not the focus
私は大きいボールが店へ投げました。
I don’t need to?
… by the way I don’t mean golden balls 
Huh? Either is grammatically fine, there’s no rule regarding which to use. But they have different nuances.
http://www.imabi.net/adnominaladjectives.htm
Also not every adjective can do that.
Thanks for clearing that up! I need to stop giving advice when I have no idea what I’m talking about. It’s a bad habit of mine.
To answer your question, your examples are correct (as far as I know).
If the adjective is directly modifying a noun, you do not conjugate it.
But if the adjective is not in front of a noun, you do need to conjugate it.
(yes, that’s what you said, just phrased differently.)
Although, now I’m getting myself confused…which one of these sentences would be correct?
隣人が投げたボールは大きいです。
隣人が投げたボールは大きかったです。
Both of those sentences are correct. They just are present vs past.
In that case, I guess I’m confused as to when each of my sentences would be appropriate to use. In English, since the event already happened, I think I would always use the past tense.
The ball the neighbor threw is big.
The ball the neighbor threw was big.
I don’t see why it has to always be past. If the ball still exists, it’s fine to use present. The past has a feeling of telling someone about it while you are not anywhere near the ball anymore.
I’m probably overthinking it, but my intuition was that the Japanese would be more likely to use the present tense even if the ball is not nearby, because the ball is still big whether you can still see it or not.
Since you mention it, I guess I could imagine using the present tense in English exclaiming about the size if you were actually looking at the ball.
I was referring just to the English, but yeah, it would be wise to try to read as many examples as you can of Japanese tenses in real use, because there are plenty of counter-intuitive situations.
hello:grinning: