Translation guide
The English suffix '-ness' turns adjectives into abstract nouns (e.g., happiness, darkness). Japanese has no single direct equivalent. Instead, use noun forms of adjectives, special suffixes, or rephrase with verbs and adjectives.
Express the quality or state of being X, where X is an adjective.
For i-adjectives, remove the final い and add さ to form a noun meaning the degree or quality of that adjective. This is the most common and productive way to express '-ness' for i-adjectives.
この部屋の広さは十分です。
The spaciousness of this room is sufficient.
I was moved by his kindness.
For na-adjectives, add さ directly to the stem to form a noun meaning the degree or quality. This is also very common.
Use こと or の to nominalize an adjective phrase, especially when describing the abstract concept rather than a measurable degree. こと is more abstract, の is more concrete or personal.
健康であることが一番大切です。
Being healthy is most important. (healthiness)
一人でいるのが好きだ。
I like being alone. (aloneness)
Some adjectives can take み to express a subjective, internal quality or flavor. This is less productive and limited to certain words (e.g., 甘み sweetness, 苦み bitterness, 深み depth).
このスープには甘みがある。
This soup has a sweetness to it.
Some adjectives have dedicated noun forms that are more natural than using さ.
The noun for 'happiness' is 幸せ, not 嬉しさ (which means degree of happiness). Use this for the state of being happy.
幸せを感じる。
I feel happiness.
The noun for 'freedom' is 自由, not 自由さ (which would mean degree of freedom).
The noun for 'health' is 健康. 健康さ would mean 'degree of healthiness'.
Japanese often prefers verbal or adjectival expressions over abstract nouns. Rephrase '-ness' words as verbs or adjectives.
Instead of saying 'the darkness of the room', say 'the room is dark' or 'the room became dark'. This is often more natural.
部屋が暗くなった。
The room became dark. (instead of 'the darkness of the room increased')
Simply state the quality as an adjective modifying the subject, rather than nominalizing it.
このケーキは甘い。
This cake is sweet. (instead of 'the sweetness of this cake')
While さ is productive, it often sounds like you're measuring a degree. For abstract concepts, use dedicated nouns or rephrase. For example, 'kindness' as a virtue is 優しさ, but 'an act of kindness' might be 親切な行為.
親切な行為
an act of kindness
さ expresses an objective, measurable degree (高さ height, 長さ length). み expresses a subjective, internal quality or flavor (甘み sweetness, 深み depth). Not all adjectives can take み.
I seek freedom.
健康が一番だ。
Health is the most important thing.