A question about the vocab 「了解」

[highliuk]

Can you explain the true meaning of 了解りょうかい? Besides the “roger, ok” meaning, which if you look over the web happens to be 90% of this word’s usage.

But if you read the example sentences for this word, it has very different meanings other than that, and I cannot understand the difference between similar words.

Let me explain it with the example sentences.

Example sentence #1

芸能人げいのうじんにＣＭシーエム出演しゅつえんの了解りょうかいを求もとめる。
I ask for the consent of the celebrities to appear in commercials.

How is that different from 承諾 or 同意?

Example sentence #2

両社りょうしゃの間あいだで了解りょうかいが成なり立たったので、取引とりひきをしました。
Since an agreement was established between both companies, we made a deal.

How is that different from 合意?

Example sentence #4

日本にほんには電車でんしゃやバスの中なかでは大声おおごえで話はなさないという暗黙あんもくの了解りょうかいがある。
In Japan, there is an unspoken understanding that you do not speak loudly on trains or buses.

How is that different from 理解 or 納得?

Also, example sentences from 5 to 8 are translated with understand as well, so I wonder if 理解 or 納得 are the same:

Sentence #5

この手紙てがみの内容ないようは意味いみ不明ふめいなので、この来信らいしんを了解りょうかいするわけにはいきません。
The content of this letter is meaningless, so there is no way we can understand this message.

Sentence #6

彼かれの英語えいごはたどたどしいので、何なにを言いっているか了解りょうかいできそうにありません。
His English is so halting that I can’t understand what he’s saying.

Sentence #7

相手あいてが一いち度どでこちらの要求ようきゅうを了解りょうかいしてくれたので、もう一度いちど説明せつめいをせずに済すみました。
Since the other party understood our request in one go, we didn’t have to explain again.

Sentence #8

僕ぼくは親友しんゆうが言いいたかった事ことを瞬時しゅんじに了解りょうかいする事ことが出来できた。長年ながねんコミュニケーションをしてきた甲斐かいがある。
I was able to instantly understand what my best friend wanted to say. It was worth having communicated for many years.

[drunkgome]

As I understand it, at its core 了解 means that information or a situation is being acknowledged or accepted as being understood. This can be similar to the English, “got it” or like you said “Roger” etc.

Example sentence 1

In example sentence 1. You’re seeking acknowledgement that the celebrity understand the proposal and is ok with its contents.

@highliuk

How is that different from 承諾 or 同意?

These are somewhat formal and express explicit or intentional consent. The example sentence seems like a more casual proposal to the celebrity which informs them of its contents and then simply asks “are you cool with that”

If the celebrity in question needed to sign a contract to express consent then perhaps 同意 or 承諾 would be better.

Example sentence 2

Example sentence 2 is similar to the first in that both companies discussed the situation and acknowledged that they understood the situation and reached an agreement based on that mutual understanding. So the nuance is like

了解 we’re on the same page
同意 we entered into a formal/contractual agreement.

Example sentences 4 & 5

Example 4 uses a set expression in 暗黙の了解 which is basically like our unspoken agreement or unwritten rule.

@highliuk

How is that different from 理解 or 納得?

理解 expresses some sort of intellectual understanding. 納得 Expresses understanding based on facts that you personally reasoned through. So the nuance is something like

了解 we all get, understand and accept this rule even if it’s not said.
理解 I know the rule exists
納得 I personally accept this rule as being reasonable.

5 is pretty much the same. You 理解 the words in the letter, but the overall meaning is unclear so you do not(can’t) understand and accept what must be done

Example sentences 6 & 7

For 6 I think both 理解 and 了解 are somewhat interchangeable, albeit with a slightly different nuance. I don’t think that nuance is big enough to make a substantial difference though.

7 is again similar. They both understood and acknowledged/accepted our explanation the first time so repeating the explanation wasn’t necessary. Nuance could be like
了解 they understood and accepted our request. Or they got it and were ok with it.
理解 they understood what we requested(the words), but did not necessarily accept or acknowledge that the understanding would lead to compliance. Or more simply. They understood what we meant.

Hopefully this makes sense. I also made a table that condenses the information and gives some nuance and examples of situations in which the word would be used based on my understanding of the words.