と同時に【とどうじに】

The expression と同時に means "at the same time as", "the moment that", or "as well as". It is used to express that two things happen simultaneously, or that something has two qualities or roles at once.

Simultaneous events

When attached to a verb in dictionary form, と同時に indicates that two actions or events occur at the same time or in very quick succession. It often conveys the nuance of "the instant" or "the moment" something happens.

This usage emphasizes that the second event happens right when the first one does – there is little or no gap between them.

Dual roles or qualities ("as well as")

When attached to a noun (often with である), と同時に can express that something or someone holds two roles, qualities, or identities at once. In this case it translates closer to "as well as" or "while also being".

With nouns (events)

When a noun represents an event or occasion, と同時に directly follows it to mean "at the same time as."

Notes

• と同時に is somewhat formal and is common in written Japanese, news, and formal speech. In casual conversation, speakers might use とどうじに同時に less frequently, opting for simpler structures like きごう〜たら or きごう〜と.
• Compared to きごう〜ながら, which describes two ongoing actions by the same person, と同時に focuses on the timing of two events coinciding and can involve different subjects.