科学
かがく
kagaku
= science / natural science
科学 (kagaku) is the Japanese word for science — the systematic study of the natural world through observation and experiment. It appears everywhere from school curricula to news headlines about space exploration and medical breakthroughs.
科学 (kagaku) refers to natural science broadly — physics, biology, astronomy, earth science, and related fields — as well as the scientific method itself. In everyday speech, kagaku can mean science as a school subject, as an academic discipline, or as a general way of understanding the world through evidence.
A critical point for learners: Japanese has two words pronounced kagaku. 科学 means science (natural science broadly), while 化学 means chemistry specifically. They are pronounced identically in speech, so context and kanji are essential for distinguishing them. In written Japanese, the difference is immediately clear from the first character.
The biggest pitfall with kagaku is the homophone trap. When someone says kagaku no jugyō (a science/chemistry class), you cannot tell from sound alone whether they mean 科学 (science) or 化学 (chemistry). Pay attention to context: are they talking about a broad science topic or a specific chemistry experiment? In written Japanese, always check the first kanji — 科 for general science, 化 for chemistry.
Also note that 科学的 (kagakuteki) means scientific (as an adjective), and 科学者 (kagakusha) means scientist. These compounds use 科学, not 化学.
科学 is written with two kanji. 科 (ka) originally depicted a grain plant being measured or sorted, and carries the meaning of department, category, or subject — as in a branch of study. 学 (gaku) means learning or study. Together, 科学 literally suggests the study of categorized knowledge, i.e., systematic, disciplined inquiry.
The homophone 化学 (chemistry) uses a different first kanji: 化 (ka), meaning change or transformation — fitting for chemistry, which studies how substances transform. Keeping these two 学 compounds separate in writing is a practical skill tested in Japanese schools and standardized exams.
Everyday use
彼女は子どものころから科学に興味があった。
Kanojo wa kodomo no koro kara kagaku ni kyōmi ga atta.
She has been interested in science since she was a child.
Casual / Social Media
最新の科学ニュース、もう読んだ？火星探査の話だって。
Saishin no kagaku nyūsu, mō yonda? Kasei tansa no hanashi datte.
Have you read the latest science news? Apparently it’s about Mars exploration.
Formal / Cultural context
科学技術の発展は現代社会に不可欠な要素となっている。
Kagaku gijutsu no hatten wa gendai shakai ni fukaketsu na yōso to natte iru.
The advancement of science and technology has become an indispensable element of modern society.
Science education in Japan is taken seriously from an early age. Elementary school students study rika (理科), a subject covering natural science basics, before the word 科学 becomes more prominent in middle and high school curricula. Japan’s emphasis on science is reflected in its internationally competitive research output and its reverence for scientists like Nobel laureate Shinya Yamanaka, whose work on iPS cells drew nationwide attention.
The distinction between 科学 (science) and 科学技術 (kagaku gijutsu, science and technology) matters in public discourse. Government agencies and policy documents often use the compound kagaku gijutsu, as in the Ministry of Education, Culture, Sports, Science and Technology (文部科学省, Monbu Kagakushō). The prominence of this ministry’s name in daily life means many Japanese people encounter 科学 as part of an institutional phrase long before they study it as a vocabulary word.
Science fiction — SF (エスエフ) in Japanese — has a devoted following in Japan, and the genre regularly uses 科学 in titles and dialogue to anchor stories in a framework of plausible natural laws. The cultural appetite for science-themed storytelling, from classic robot manga to contemporary hard-SF novels, has kept 科学 a word with both pragmatic and imaginative connotations for Japanese readers.