So I know that to make an adverb, you use 'de/di' and put it before the verb like:
我兴奋地打开了我的礼物
But in my studies this week I saw this:
...病症的人逐年增加
and
逐渐成长为独立
Am I right in thinking that these are simply adverbs but to make an adverb from an adjective like 好 or 兴奋 you need a 地？
地 only CHANGES ADJECTIVES to adverb. Any adverbs without being conjugated from adjectives can exist without 地.
地 is commonly omitted. This happens usually when the adjective has ONE CHARACTER only. For example: 慢慢走 or 慢走. 地 is omitted since 慢 has only ONE character. The repetition of 慢 here is only for the purpose of expressing the action in a more visualized or vivid way.
兴奋 has two characters, and you cannot shorten it to one character to have the same meaning, so we usually don't omit 地 in this case.
(It's been a week, but hope this helps)
There are plenty. Consider:
這台機器早晚會出事情。
快給我你的帳單！
我時常搭地鐵去上班。
In these phrases, the functions of 早晚, 快 and 時常 are mostly apt to be seen as adverbs. This being said, the POS in Chinese is not very well-agreed.
This is due to lack of morphological markers.
In the ancient time there is no 地 marker, and adjectives also functions as adverbs (like German).
In these cases, arguably they also look like the complementary adjectives of the subject.
I guess its advent is probably 20 century, when phrases are so complicated that we often have difficulty parsing, and English-like structures are borrowed into written Chinese.
So back to the question, I would say that when a adverb doesn't cause ambiguity, 地 is often not added. The examples
(a)我兴奋地打开了我的礼物。
(b)我兴奋打开了我的礼物。
In (b), it cause some confusion (at least when the eye has parsed to 兴奋) what 兴奋 functions as. But in (b), suffices to say, 地 clears up confusion by reminding you a verb is following.
Last I shall note that even scholars often disagree, as modern Mandarin grammar is not well restricted, and native speakers are generally very tolerant with non-standard phrases.
I found a discussion. You shall notice that the general consensus does not deem 地 to be not compulsory.
So, append 地 from an adjective if the adjective is several-Charactered (so more difficult to parse), or when the phrase is complicated so that confusion arises.
An adv doesn't have to be followed by a “地“, such like in "慢慢走“／”好好干“. However, you can always check if a word is an adv by adding a "地" and see if it still make sense. If "yes", then it's an adv. E.g., "慢慢地走"／“好好地干”。
