と同時に|とどうじに
- 1One event occurs at the same moment as another, or immediately after it.Ex. 1
- 2One person or thing has two qualities or roles at the same time.Ex. 2
Pairing: the second clause often contains も when presenting coexisting roles or qualities
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Neutral to slightly formal, と同時に is used for an immediate reaction to an event or to present two coexisting aspects of one subject. Unlike ながら or つつ, its event sense can pinpoint the moment something happens rather than describe two ongoing actions.
Do not use と同時に for gradual, proportional change over time.
Note that the event sense accepts 動詞た形 as well as 動詞辞書形, as in 鳴ったと同時に.
- と共にN3「と共に」 is close to 「と同時に」 in the senses of 'happening at the same time' and 'combining two sides,' and in those uses the two are interchangeable, but 「と共に」 is more literary and does not stress the exact same instant. It can also mean 'together with...' or 'changing along with...,' uses 「と同時に」 does not have.
- ながら / いながら / ながらもN3「ながら」 attaches to the ます-stem and describes two actions by the same subject continuing in parallel, while 「と同時に」 stresses the very same instant and allows different subjects. 「ながら(も)」 can also express contrast, which differs from the 'both... and...' sense of 「と同時に」.
- つつN2「つつ」 attaches to a verb's 連用形 (continuative form), is literary in style, and describes two actions by the same subject continuing in parallel; it also has a concessive (contrast) use. 「と同時に」 stresses that things happen at the very same instant, allows different subjects, and can also express two sides of something, so the two are generally not interchangeable.
- につれてN3「につれて」 describes the two parts changing gradually and in mutual linkage, while 「と同時に」 stresses occurrence at the same moment; when describing two changes advancing in sync, the two can sometimes be interchanged, but the emphasis differs. The 'both... and...' sense has nothing to do with 「につれて」.
- 一方でN3「一方で」 has no use for expressing simultaneity in time; it is close to 「と同時に」 only in the 'combining two sides' sense, where the two are interchangeable. However, 「一方で」 focuses more on contrasting opposite sides, can also contrast different subjects, and can even stand alone at the start of a sentence as a connective.
- にしたがってN3「にしたがって」 indicates a gradual change bringing about the change that follows, or 'in accordance with' a rule, while 「と同時に」 stresses the same moment or the combination of two sides; when two changes advance in step, either can be used, but 「にしたがって」 emphasizes gradual linkage. Note that 「にしたがって」 does not attach to the た form.
と共に can also express simultaneity but additionally means “together with”; ながら, いながら, ながらも, and つつ can describe overlapping actions or express contrast. につれて and にしたがって indicate gradual change, while 一方で contrasts two aspects rather than simply presenting them together.
