Translation guide
The English verb 'deepen' can be used for physical depth, intensifying abstract qualities, or making something more profound. In Japanese, there is no single direct equivalent; the translation depends heavily on the context. This guide covers the most common ways to express these ideas naturally.
To increase the physical depth of something, such as a hole, a river, or a container.
The most straightforward way to say 'make deeper'. It uses the adjective 深い (deep) in its adverbial form 深く plus する (to do/make).
川を深くする工事が始まった。
Construction work to deepen the river has begun.
Please make the hole a little deeper.
Literally 'dig down', used when deepening by digging, such as a hole or a trench. It can also be used metaphorically for delving into a topic.
井戸を掘り下げる必要がある。
We need to deepen the well.
A transitive verb meaning 'to deepen', but it is rarely used for physical depth. It is more common in abstract contexts (see next meaning). Using it for physical depth can sound literary or unusual.
Avoid using 深める for physical depth in everyday speech; use 深くする instead.
池の底を深める。
Deepen the bottom of the pond. (literary/technical)
To make a feeling, relationship, understanding, color, or other abstract quality stronger or more intense.
The most common transitive verb for abstract deepening. It is used with nouns like 理解 (understanding), 関係 (relationship), 絆 (bonds), 知識 (knowledge), etc.
お互いの理解を深めることが大切です。
It is important to deepen mutual understanding.
友情を深めるために旅行に行った。
We went on a trip to deepen our friendship.
Means 'to strengthen' or 'intensify'. It is used when 'deepen' implies making something more powerful or pronounced, such as a color, impression, or suspicion.
Intransitive verb meaning 'to deepen' (become deeper). Use this when the subject itself deepens, not when someone deepens something.
A more analytical phrase using 深くする, similar to the physical meaning but applied to abstract nouns. It is less common than 深める but still natural.
知識を深くするために勉強を続けている。
I continue studying to deepen my knowledge.
A formal, technical term meaning 'to deepen' or 'to intensify', often used in academic or business contexts. It is a Sino-Japanese compound (深化 + させる).
両国の協力関係を深化させる必要がある。
It is necessary to deepen the cooperative relationship between the two countries.
To make a voice or sound deeper, as in lower pitch.
Literally 'make one's voice low'. This is the most natural way to say 'deepen one's voice'.
彼は意識的に声を低くして話した。
He deliberately deepened his voice when speaking.
Transitive verb meaning 'to lower (pitch, volume, etc.)'. It can be used for voices or sounds.
声のトーンを低める。
Lower/deepen the tone of one's voice.
To become deeper in a physical or abstract sense, without an agent causing it.
The most common intransitive expression for physical or abstract deepening. It uses the adjective 深い (deep) in its adverbial form 深く plus なる (to become).
川が雨で深くなった。
The river deepened due to the rain.
彼の知識は日々深くなっている。
His knowledge is deepening day by day.
Intransitive verb meaning 'to deepen', often used for abstract things like seasons, relationships, or understanding. It implies a natural progression.
深める (fukameru) is transitive (someone deepens something), while 深まる (fukamaru) is intransitive (something deepens on its own). Choose based on whether there is a direct object.
Do not assume 'deepen' can always be translated as 深める. For physical depth, 深くする is more natural. For intensifying colors or sounds, 強める or 低くする may be better.
It was a remark that deepened the suspicion.
色を強めるために絵の具を足した。
I added paint to deepen the color.
As autumn deepens, the leaves become more beautiful.
二人の絆が深まった。
The bond between the two deepened.
秋が深まる。
Autumn deepens.