魚心あれば水心あり: what does 心 do exactly?

Question

According to JapanDict, this proverb literally means "if a fish is friendly toward water, water will be kind to the fish too" (although Wiktionary says it's the other way around...). Is that really a literal translation? If it is, then where does this idea of friendliness come from? Do you get "a caring fish" by putting 魚 and 心 together? Can you do the same with other living creatures? Or does 魚心 only make sense when we look at the full phrase? Is it perhaps something like "when there is a fish with a (kind) heart, there is also water with a (kind) heart"?

Whatever the literal meaning is, is it obvious to a native speaker when they hear the proverb for the first time? Or do they need some mental effort to figure out how 心 works here?

Then there is stuff like 乙女心... Does it have any relation to this?

Answer 1

Well, ... if anything, since the -心【ごころ】 is productive i.e. can attach to everything, you can make a word like 魚心 that means "fish mindset" or "fish sentiment", but it still doesn't make sense.

The truth is inside dictionaries:

うお‐ごころ〔うを‐〕【魚心】
《「魚、心あれば」が誤って一語になったもの》相手に対する好意。（デジタル大辞泉）

うお‐ごころ［うを：］ 【魚心】
「うおごころ（魚心）あれば水心」によった語。「魚、心あれば」を誤って「うおごころ」と一語にしたもの。（日本国語大辞典）

So, it was actually a misreading! The correct reading was 「魚【うお】 (pause) 心【こころ】あれば、水【みず】 (pause) 心【こころ】あり」, and 心ある means "be considerate, compassionate", here is no more mystery.

This kind of phenomenon is called "rebracketing", and observable in any language. For example, English orange used to be norange, but at some time they took it as "an orange".