惰性

• Reading: だせい
• Romaji: dasei
• Kanji breakdown: 惰 (da) — lazy, indolent, idle; 性 (sei/shō) — nature, tendency, inertia
• Pronunciation: /dase̞i/

Meaning

Inertia; force of habit; doing something out of momentum rather than intention. Continuing a behaviour simply because it has always been done.

A formal noun. In physics it refers to inertia; in emotional and behavioural contexts it describes acting on autopilot — continuing relationships, jobs, or habits not out of will or desire but out of passive momentum. Carries a mildly negative nuance, suggesting lack of reflection or initiative. The phrase 惰性で〜する (to do something out of inertia/habit) is a common construction used in self-critical or observational speech.

Examples

1. 二人の関係はすでに惰性で続いているだけで、愛情は残っていなかった。 Their relationship was continuing merely out of inertia, with no love remaining.
2. 惰性で同じ仕事を続けていても、成長はない。 You won't grow if you just keep doing the same job out of sheer momentum.
3. 彼は惰性でテレビを見ていたが、心はどこか遠くにあった。 He was watching TV out of habit, but his mind was somewhere far away.

Usage Guide

Context: relationships, work, lifestyle, self-reflection

Tone: critical

Origin & History

Compound of 惰 (da — lazy, idle, indolent) and 性 (sei/shō — nature, tendency, property). The character 性 here evokes a stable, persistent tendency — the 'nature of idleness' that keeps things moving without deliberate effort.

Cultural Context

Era: Modern

Generation: All ages

Social background: Universal