How to say "science" in Japanese

• 科学かがくJLPT N4approx.Common
  nounThe default word for science as a field of knowledge and activity. Use it in ordinary talk and writing about scientific research and progress; it is what 'science' usually means.
  科学かがくは観察かんさつに基もとづいている。↗

  Science rests upon observation.
• 理科りかJLPT N2approx.Common
  nounCovers science as a school subject and the natural-sciences grouping, which takes in mathematics, engineering and medicine, as opposed to the humanities. Typical contexts are classrooms, curricula and choice of study track.
  彼女かのじょは理科りかを勉強べんきょうしなければなりません。↗

  She has to study science.
• サイエンスCommon
  nounThe loanword from English, used chiefly in names, titles and borrowed phrases. In running prose it is seldom the word you want for 'science'; 科学 is the natural choice.
• 学術がくじゅつJLPT N2approx.Common
  nounPoints to scholarship and the academic world as a whole — 'arts and sciences' — rather than science specifically. Seldom the word you want for plain 'science'; it is closer to 'academic'.
  彼かれは学術がくじゅつ会議かいぎに出席しゅっせきした。↗

  He attended the scientific conference.
• 学問がくもんJLPT N3approx.Common
  nounA branch of learning or discipline; '(a) science' in the sense of a systematic field of study, not the natural sciences. Typical of talk about study and scholarship; for science itself use 科学.
  心理学しんりがくは心こころを科学かがく研究けんきゅうする学問がくもんである。↗

  Psychology is the scientific study of the mind.

Use 科学 for science in general, 理科 for the school subject and the natural-sciences side of study, 「サイエンス」 in names and borrowed phrases, and 学問 or 学術 for scholarship and disciplines rather than science proper.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

• 科学かがくscience
• 理科りかscience (natural sciences and related fields, incl. mathematics, engineering, medicine, etc.)
• サイエンスscience
• 学術がくじゅつscience
• サイエンスScience (journal)
• 理学りがく(physical) science
• 学問がくもんdiscipline