理解 (rikai) means “understanding” or “comprehension.” As 理解する, it means to understand an idea, explanation, or situation. 分かる is common in everyday conversation, while 理解する can sound more deliberate or formal. 理解できる means “can understand.”
past forms rikaishita / rikaidekita / rikaisaseta
understanding · comprehension · grasp
Sentences
6 sentences, word by word
理解する · plain past
plain
。
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彼
かれ ［1］
he; him
pronoun · also means boyfriend in the right context
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の
の
links noun to noun
particle · A の B = B belonging to A
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説明
せつめい ［0］
explanation
noun · 説明する is the verb form
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を
を
marks the direct object
particle · pronounced お
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やっと
やっと
finally; at last
adverb · carries the relief of a wait that is over
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理解した
りかいした ［1］
understood it
plain past of 理解する · rikaishita
理解するN3to understand
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I finally understood his explanation.
理解している · the state you are in
polite
。
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ルール
ルール ［1］
rule; the rules
noun · borrowed, and more common than 規則 in speech
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は
は
as for — the topic
particle · written は, read わ
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ちゃんと
ちゃんと
properly; all of it
adverb · casual, and everywhere in spoken Japanese
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理解しています
りかいしています
I understand — and still do
polite ている of 理解する · a state, not a promise
理解しているN3understand — the state
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I understand the rules, properly.
理解できる · potential
plain
、。
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何度も
なんども
over and over
何度 how many times ＋ も, which turns a question into 'many'
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読んで
よんで
read it, and…
て-form of 読む · glues this clause onto the next
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意味
いみ ［1］
meaning; the sense of it
noun · 意味がわかる is the set phrase
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が
が
marks the subject
particle · what the sentence is about — with 好き, 分かる and potentials, the object
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理解できた
りかいできた
was able to understand it
plain past potential of 理解する · rikaidekita
理解できるN3be able to understand
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I read it over and over, and the meaning finally came clear.
理解させる · causative
plain past
。
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先生
せんせい ［3］
teacher
noun · also how you address doctors and lawyers
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は
は
as for — the topic
particle · written は, read わ
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学生
がくせい ［0］
student
noun · university students; 生徒 for school pupils
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に
に
to — the one made to do it
particle · marks the second actor in a causative
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文法
ぶんぽう ［0］
grammar
noun · 文 sentence ＋ 法 rule
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を
を
marks the direct object
particle · pronounced お
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理解させた
りかいさせた
made them understand it
plain past causative of 理解する · rikaisaseta
理解させるN3make someone understand
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The teacher got the students to understand the grammar.
理解 with no する at all
polite
。
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日本文化
にほんぶんか
Japanese culture
compound noun · 日本 ＋ 文化, and no の between them
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の
の
links noun to noun
particle · A の B = B belonging to A
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理解
りかい ［1］
understanding
noun · the thing itself, standing on its own
理解N3understanding
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を
を
marks the direct object
particle · pronounced お
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深めたい
ふかめたい
want to deepen
深める to deepen ＋ たい · 理解を深める is the set phrase
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です
です
polite ending
copula · here it only lifts 深めたい into polite speech
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I want to deepen my understanding of Japanese culture.
理解 vs 了解
plain
、。
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内容
ないよう ［0］
the content; what it says
noun · 内 inside ＋ 容 form
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は
は
as for — the topic
particle · written は, read わ
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理解した
りかいした ［1］
understood it
plain past of 理解する · the comprehension half
理解するN3to understand
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けど
けど
but
conjunction · the casual one; が and しかし are the formal twins
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了解
りょうかい ［0］
acknowledgement; consent
noun · agreeing to do it, not following why
了解N3roger; will do
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できない
できない
cannot do
negative potential of する · the する here belongs to 了解
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I understand what it says. I can't agree to it.
Forms
What forms does 理解 take?
Noun ＋ を＋理解する
問題を理解する. The thing understood is a direct object, so it takes を. Past 理解した (rikaishita), polite 理解しました.
Noun ＋ を＋理解している
理解しています explicitly describes a current state of understanding. 理解します may express intention or a general habit, depending on context.
Noun ＋ が＋理解できる
The potential often uses が: 説明が理解できる. Past 理解できた (rikaidekita) — the closest Japanese gets to “it finally clicked.”
Person ＋ に＋理解させる
Causative: 学生に文法を理解させる. The person you get through to takes に, the thing you get across takes を. Past 理解させた (rikaisaseta).
Meaning
理解 vs 分かる vs 了解 — which one do you want?
理解 is understanding as an achievement. You took something apart, saw how the pieces fit, and now you hold it. That is why it attaches to things with structure — an argument, a rule, a system, why somebody did what they did — and why it sounds a size too formal for “got it, thanks.”
分かる happens to you; 理解する is something you do.分かる is intransitive and marks what it understands with が — 日本語が分かる, Japanese makes sense to me. 理解する is transitive and takes を — 日本語を理解する, I understand Japanese, with the effort still visible in it. In conversation 分かりました is the normal reply; 理解しました lands like “I have processed your statement.”
了解 is agreement, not comprehension. It answers an instruction — got it, I will do it — and says nothing about whether you follow the reasoning. It is what you fire back to a colleague on chat. Watch the register, though: 了解しました reads brusque upward, and 承知しました or かしこまりました are the safe ones to a manager or a client.
Talking about your current understanding.理解しています clearly describes your present state. 理解します can express intention or a general habit, depending on context. In a quick reply, 分かりました is often the more natural choice. 理解していません clearly says you do not currently understand.
Inside the word
理 ＋ 解 — where the meaning comes from
理 — り · pattern, principle, reason
The oldest sense is the grain in a piece of jade: the lines already running through the stone that tell a cutter where it will split. From there it became the pattern inside anything — 理由 reason, 物理 physics, 心理 psychology, 料理 cooking, which is arranging things properly, and 無理, no pattern, impossible.
解 — かい · untie, take apart, solve
A knife 刀, a horn 角 and an ox 牛 — butchering, which in classical Chinese thought is the model of understanding something: find the joints, separate at them. It gives you 解決 resolving, 解答 an answer, 分解 taking apart, and 解く, to solve.
理解 — りかい · read the pattern, take it apart
Both characters keep their ordinary on-yomi, so the compound is just りかい — no rendaku, no irregular reading to memorise, and the accent falls on the first mora. The two halves also say what the word does. That is why 理解 is understanding you worked for, and 分かる is understanding that showed up.
Watch out
Where 理解 goes wrong
Saying 理解します when you mean “I understand”
理解します can sound like an intention in this context. For a current state you can say 理解しています, or in many conversations 分かりました.
Sending 了解しました to your boss
It is everywhere in chat between colleagues, and it is the one form that stings upward: 了解 carries a faint air of a superior acknowledging a subordinate. To a manager use 承知しました, and to customers かしこまりました.
Keeping を after adding できる
説明を理解する is right, and so is 説明が理解できる. The potential turns the object into a subject, so を becomes が. You will hear 説明を理解できる often enough that nobody will stop you, but が is what gets marked correct.
Also asked
Questions people ask about 理解
What does 理解した (rikaishita) mean?
Understood it — the plain past of 理解する, a moment of comprehension that has already landed. The polite form is 理解しました. Between friends you would actually say 分かった; 理解した belongs to writing, study and anything with an argument in it.
What does 理解できた (rikaidekita) mean?
I was able to understand it — the past potential, and the closest Japanese gets to “it clicked.” Watch the particle: 説明が理解できた with が, because the potential makes the explanation the subject. The negative 理解できなかった is how you say you could not follow it.
What does 理解させた (rikaisaseta) mean?
Made them understand it — the past causative. The person you got through to takes に and the thing you got across takes を: 学生に文法を理解させた. It is a teacher's word, and it does carry authority, so it is not what you say about persuading a friend.
理解 or 分かる — which should I use?
分かる for almost all speech. It is intransitive, takes が, and frames understanding as something that happened to you. 理解する is transitive, takes を, and frames it as work you did — right for essays, explanations, and anything with structure to it.
Is 了解 the same as 理解?
No. 了解 is “got it, will do” — it acknowledges an instruction and claims nothing about comprehension. 理解 is the comprehension and claims nothing about compliance. You can honestly say 理解はしたが、了解できない: I follow you, I am not agreeing.
How is 理解 read, and can I write it in kana?
りかい. Both characters take their ordinary on-yomi and neither changes, which is not always true of compounds. The pitch is head-high — り is high and everything after it drops, including a following particle. Kana is fine in your own notes, but both characters are standard and 理解 is written in kanji everywhere else.
References
Sources and usage notes
Kotobank: 理解 — Defines 理解 as grasping content or reasoning and understanding another person’s position.
