Is there any source that better explains the difference between synonyms in Korean?
For example, TTMIK has a series of videos like this: https://www.youtube.com/watch?v=Ctb2czA1nVM=em-uploademail
Explaining the difference between synonyms. In this example, the two words mean "to recommend" but 추천하다 is for recommending anything and 권하다 can be when you are offering food or drinks.
Naver Dictionary has a few example sentences to go with the word but still sort of just says "to recommend".
Should I just ask native speakers?
I think the explanation of (near)synonyms is a very difficult task. The usage may differ from one region to another, from one social group to another. There may be overlaps, there may be developments in the language that do away with distinctions that were relevant in the past.
So it's very difficult for dictionaries to give "that one allowable" usage for each of them.
Therefore, I think that a language forum like this one is a good place to ask about synonyms, but not in a general way, but rather one in each thread.
In this way, people who have experience with the language can explain their individual understanding and usage of this one pair of synonyms, and in the course of the discussion, a pattern may emerge -- or not, and this would be an insight in itself.
This is a grand Q indeed! Below are some of my thoughts on this:
1) It would help learners a lot if Duolingo Example Sentence designs take this matter into consideration - Not sure if the course contributors can do much about this at this point or else.
A well-designed example sentence in Korean should be able to teach a lot of things at once: grammar rules, tricky spellings, exact usage of certain confusing vocabulary and idiomatic expressions etc.
2) Hope you expose yourself to Korean contents more (preferably videos rather than audio and text, something more straightforward rather than something open for various interpretations) to strengthen your understanding of vocabulary you built initially. Grasping which words and expressions you initially memorized are used in exactly which contexts are very important.
"Follow Me" by BBC and "French Action" by Princeton Univ. are all taking full advantage of videos to help the learners of English/ French learn new words and expressions by giving rich contextual info in the form of short stories. Not sure what the exact equivalent is for Korean yet.
Maybe you can watch the news in Korean on SBS since you are a Queenslander perhaps? Believe it is the same English news for Australians delivered in Korean meaning you know what they are talking about and all you need to do is just observe which words, expressions are used.
This channel should also help a bit:
Actually, Naver is an excellent source. You might try looking up each Korean word in both translation sections (국어 and 엉어) If you click on the word (in either section) another page will open up with many more examples. Then you might try entering the English word, and can arrive at http://endic.naver.com/search.nhn?sLn=kr&isOnlyViewEE=N&query=recommend
You can search further by clicking on the word again (in blue) and it will take you to another page with more examples. http://endic.naver.com/enkrEntry.nhn?sLn=kr&entryId=472081b5aae847c0bb2db4107287565a&query=recommend
Even though both 추천하다 and , 권하다 can both be defined as "recommend", they are not really synonyms in the strictest sense of the word. since they are used in different situations to convey different meanings as the TTMIK video points out. Language is made more interesting and challenging by the fact a given word can have multiple meanings.
Interestingly, Naver lists 권고하다, or 종용하다 as synonyms for 권하다. For 추천하다, it lists 밀다, or 소개하다.
As you point out, 추천하다 is used for saying something or some person is good, when you recommend a good book, a movie, a restaurant, a person, etc.
권하다 is for much more than just offering food or drink. It is used when "recommend" has the meaning of advise or suggest, usually relative to a course of action.