さAdjective-to-noun suffix
さ turns an adjective into a noun naming its quality, state, or degree: for example, “high” becomes “height.”
The result behaves like a noun
After adding さ, the new word is a noun. It can be modified by another noun with の and can take ordinary noun particles such as は, が, を, and に.
Naming a quality or degree
A neutral degree versus a characteristic quality
さ is the broad, neutral default for naming a quality or its degree. み is used with a more limited set of established words and often presents a quality as something sensed, distinctive, or concretely present. Do not assume that every adjective can freely take み.
このコーヒーは苦さが強いが、後に残る苦みはない。
This coffee is very bitter, but it has no lingering bitter taste.
Analyze苦さ expresses the degree of bitterness, while 苦み presents bitterness as a taste quality.
More examples
この箱の重さは二キロです。
This box weighs two kilograms.
Analyze計画には柔軟さが必要です。
A plan needs flexibility.
Analyze山の美しさを写真だけで伝えるのは難しい。
It is difficult to convey the beauty of the mountain through photographs alone.
Analyze子どもにもこのゲームの面白さが分かった。
The child also came to appreciate what makes this game interesting.
Analyze部屋の明るさを少し下げました。
I lowered the brightness of the room a little.
Analyze使ってみて、この製品の便利さに気づきました。
After trying it, I realized how convenient this product is.
Analyze