科 — Subject, Department, Science

Meaning

The kanji 科 carries the core meaning of subject, department, course of study, and classification. It turns up across education, medicine, biology, and law — one of those characters that follows you from grade school through adulthood. In academic contexts, 科 refers to a school subject or a university department — for example, the science subject taught in school or the medical department at a hospital. In biological taxonomy, 科 denotes a family of organisms (e.g., the cat family, the rose family). In legal or classical contexts, it can also mean an offense or crime, though this usage is less common in everyday speech.

Etymologically, 科 is a compound ideograph (会意文字, kaii moji) composed of two elements: 禾 (the rice plant or grain stalk) on the left, and 斗 (a measuring ladle or dipper used to measure grain) on the right. The original meaning was "to measure and sort grain into categories." From that act of systematic sorting, the meaning expanded outward — into academic departments, medical specialties, and biological families. That leap from sorting grain to classifying knowledge shows how concrete, physical actions gave birth to abstract vocabulary.

科 has 9 strokes and is classified as a Grade 2 elementary school kanji in Japan, meaning Japanese children learn it around age 7–8. Its early placement in the curriculum reflects how central this character is to everyday Japanese.

Readings

On'yomi (音読み) — Chinese-derived readings

科 has one primary on'yomi reading: カ (ka). It derives from the old Chinese pronunciation and is overwhelmingly the most common reading today. Almost all compound words containing 科 use the カ reading. School subjects, hospital departments, and scientific terms all use this reading.

科学かがく (kagaku) — science, natural science

理科りか (rika) — science (as a school subject, especially natural sciences)

外科げか (geka) — surgery, surgical department

内科ないか (naika) — internal medicine, medical department

教科きょうか (kyōka) — school subject, academic subject

Kun'yomi (訓読み) — Native Japanese readings

科 has no standard kun'yomi reading in modern Japanese. This is common for kanji borrowed from Chinese to fill a gap — abstract concepts that had no native Japanese equivalent. All compounds use the on'yomi カ. When you see 科 in a text, read it as か (ka).

Common Words & Compounds

科 appears in a wide range of compound words spanning education, medicine, biology, and everyday life. The compounds below are organized by theme to help you build vocabulary systematically.

Education & Academic Fields

科学かがく (kagaku) — science, natural science; one of the most common words in Japanese
教科書きょうかしょ (kyōkasho) — textbook; literally "subject-lesson book"
理科りか (rika) — science class (elementary/middle school subject)
社会科しゃかいか (shakaika) — social studies (school subject)
家庭科かていか (kateika) — home economics (school subject)
学科がっか (gakka) — field of study, course, department (university)
文科ぶんか (bunka) — liberal arts, humanities department
百科事典ひゃっかじてん (hyakkajiten) — encyclopedia; literally "hundred-subject reference"

Medicine & Healthcare

外科げか (geka) — surgery department, surgical medicine
内科ないか (naika) — internal medicine department
歯科しか (shika) — dentistry, dental department
眼科がんか (ganka) — ophthalmology, eye clinic
小児科しょうにか (shōnika) — pediatrics, children's medicine

Law & Other Uses

前科ぜんか (zenka) — criminal record, prior offense
科料かりょう (karyō) — a minor fine (legal penalty)

Example Sentences

科学かがくのおかげで、多おおくの病気びょうきが治なおせるようになった。

Kagaku no okage de, ōku no byōki ga naoseru yō ni natta.

Thanks to science, many diseases can now be treated.

彼女かのじょは理科りかがとても得意とくいです。

Kanojo wa rika ga totemo tokui desu.

She is very good at science class.

教科書きょうかしょを忘わすれてしまいました。

Kyōkasho wo wasurete shimaimashita.

I accidentally forgot my textbook.

お腹おなかが痛いたいので、内科ないかに行いきました。

Onaka ga itai no de, naika ni ikimashita.

Because my stomach hurt, I went to the internal medicine department.

外科げかの手術しゅじゅつは成功せいこうしました。

Geka no shujutsu wa seikō shimashita.

The surgical operation was a success.

歯科しかに行いって、虫歯むしばを治なおしてもらいました。

Shika ni itte, mushiba wo naoshite moraimashita.

I went to the dentist and had my cavity treated.

彼かれは大学だいがくで理学りがく部ぶ物理ぶつり学科がっかに所属しょぞくしています。

Kare wa daigaku de rigakubu butsurigakka ni shozoku shite imasu.

He belongs to the physics department in the Faculty of Science at university.

百科事典ひゃっかじてんで調しらべると、詳くわしい情報じょうほうが見みつかります。

Hyakkajiten de shiraberu to, kuwashii jōhō ga mitsukarimasu.

If you look it up in an encyclopedia, you will find detailed information.

あの病院びょういんには眼科がんかと小児科しょうにかがあります。

Ano byōin ni wa ganka to shōnika ga arimasu.

That hospital has an ophthalmology department and a pediatrics department.

彼女かのじょは前科ぜんかがないので、就職しゅうしょくに問題もんだいはないでしょう。

Kanojo wa zenka ga nai no de, shūshoku ni mondai wa nai deshō.

Since she has no criminal record, there should be no problem with her job search.

Memory Tip

Picture a farmer using a large ladle (斗) to measure and sort harvested grain (禾) into separate buckets — one for each category. That sorting action is the core of 科: organizing things into their proper group. 学科, 外科, ネコ科 — each is just a different kind of bucket. The left component 禾 looks like a plant leaning in the wind; the right component 斗 suggests a scooping motion.