確率

• Reading: かくりつ
• Romaji: kakuritsu
• Kanji breakdown: 確 (kaku) — certain, definite; 率 (ritsu) — rate, ratio
• Pronunciation: /ka.kɯ.ɾi.tsɯ/

Meaning

Probability; likelihood. A numerical measure of the likelihood that a given event will occur, expressed as a value between 0 and 1.

One of the most fundamental concepts in mathematics and statistics. 確率論 (probability theory) underpins statistics, quantum mechanics, information theory, and finance. In everyday Japanese, 確率 is commonly used to express odds or chances (e.g., 雨が降る確率は70パーセント — there is a 70% chance of rain). Related terms: 条件付き確率 (conditional probability), 確率変数 (random variable), 確率分布 (probability distribution). Distinguished from 可能性 (kanōsei — possibility), which is more informal.

Examples

1. このコインを投げたとき、表が出る確率は理論上50パーセントだ。 When this coin is tossed, the theoretical probability of it landing heads is 50%.
2. 統計学における確率論は、不確実な現象を定量的に扱うための数学的基盤を提供する。 Probability theory in statistics provides the mathematical foundation for quantitatively handling uncertain phenomena.
3. 機械学習モデルは各クラスに属する確率を出力し、最も高い値のラベルを予測として返す。 A machine learning model outputs the probability of belonging to each class and returns the label with the highest value as its prediction.

Usage Guide

Context: mathematics, statistics, physics, data science, everyday language

Tone: technical to neutral

Origin & History

Meiji-era Sino-Japanese translation: 確 (kaku) — certain, definite + 率 (ritsu) — rate, ratio. Coined to render the mathematical concept of 'probability' from Western mathematics. 率 is widely used in Japanese for ratios and rates (利率, 速率, 税率).

Cultural Context

Era: Meiji-Modern

Generation: All ages

Social background: Universal