One great problem of learning from textbooks and grammar sites is that they tend to treat many aspects of Japanese as if they were a list of arbitrary rules that just have to be learned.
In most cases, such as the rules governing i- and na-adjectives or the use of sou to mean “seems like” or “I heard”, there is nothing arbitrary about them at all. Once you understand what the textbooks don’t tell you, they make perfect sense.
The same is true of ki ga suru, ki ni suru and ki ni naru. So, what is the secret? How do we tell them apart?
Watch the Particles
In a magic show you keep your eye on the magician’s hands. In Japanese you keep your eye on the particles. They are often the primary clue as to what is going on.
In all cases the particle-marked noun is ki – one’s spirit, thoughts or feelings.
Ki ga suru
気がする uses the active ga-particle. In other words, your spirit is doing something. It is active. What your spirit is doing is having a feeling or a hunch. It may also be wanting to do something. In all cases your ki takes the initiative. It is your feeling, your impetus.
Ki ni naru
In 気になる ki is marked by the passive ni-particle and uses the passive naru rather than the active suru. Something is happening to your spirit. It may be worrying you, arousing your curiosity or your desire. But it is all more passive than ki ga suru.
Ki ni suru
With 気にする we are back to the active suru verb, but the marker is the passive ni. This means that something is being done to your spirit. It is almost the reverse of ki ga suru. The tone of this is much more negative. Something is worrying you, literally preying on your mind.
Ki ni suru is often used negatively, as in ki ni shinaide (don’t worry), ki ni shinai (I don’t care/it doesn’t bother me).
While these expressions ovelap to some extent, they are distinct in nuance.
Ki ga suru and ki ni suru are the furthest apart in meaning and barely overlap at all, whereas ki ni naru comes in between and, depending on usage, will be closer to one or the other.
But as you see, it is not a question of rote-learning. The expressions mean what they mean because of the way they are constructed. Once we understand them, we are much more likely to remember them and use them correctly.
Japanese does make sense!
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