Synonym Boundary: "決める", "決心する", "〜ことにする", "定める"

When expressing "decide" in Japanese, you must carefully distinguish between "決める", "決心する", "〜ことにする", "定める" based on context.

• 決める (きめる (kimeru) - Level: N4): Maps to "to decide" and is used when Transitive verb. Used for making a decision, setting a plan, or determining something. Can also mean to fix or settle..
• 決心する (けっしんする (kesshinsuru) - Level: N3): Maps to "to decide, to make up one's mind, to resolve" and is used when Implies a firm, strong decision or resolution, often made after careful thought or overcoming hesitation. It is a する-verb..
• 〜ことにする (〜ことにする (〜koto ni suru) - Level: N3): Maps to "to decide to, to make a point of, to choose to" and is used when Expresses a personal decision or resolution made by the speaker. It's about 'making it a rule' or 'deciding' to do something. Contrast with 「〜ことになる」which implies a decision made by others or circumstances..
• 定める (さだめる (sadameru) - Level: N2): Maps to "to decide, to establish, to set, to determine" and is used when Often implies making a formal decision, setting rules, or determining a course of action. More formal or definitive than 決める.

Mixing these up can easily lead to unnatural translations. Refer to the bilingual context cards below to master the boundaries!