と共(とも)にTogether with, At the same time, As well as

と is a basic particle used to connect nouns, similar to 'and' in English, commonly appearing in both speech and writing. と共に, however, is a formal expression meaning 'along with' or 'at the same time as,' and is used with verbs, adjectives, or nouns. It often suggests a mutual or deeper connection, unlike と, which simply connects items without implying additional nuance.

Both と and と共に express mutual action or relation, similar to the English 'with.' と is more common and used in everyday speech and writing, but it only follows nouns (e.g., 友だちと遊ぶ = 'play with a friend'). In contrast, と共に is more formal, appearing in written Japanese or structured speech, and can follow verbs, adjectives, and nouns.