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

に伴って・に伴い and と共に both express things happening in connection with another event. と共に emphasizes simultaneity or shared experience, e.g. '成長と共に責任も増える' ('Responsibility grows along with maturity'). に伴って・に伴い emphasizes causality or consequential change, often in formal contexts, e.g. '経済の発展に伴って生活水準が向上した' ('As the economy developed, living standards improved').

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 relate to the idea of doing something 'together', but with different nuances and usage. 合う attaches to verb stems to convey mutual interaction, e.g. 助け合う ('help each other'), while と共に means '(A) happens together with (B)' in the sense of co-existence or simultaneity, e.g. 年を取ると共に考え方も変わった ('My thinking changed as I grew up').

と並んで and と共に both suggest pairing, but with different focuses. と並んで stresses equal footing or value, e.g. '村上春樹と並んで人気の日本人作家' ('a Japanese author as popular as Haruki Murakami'). と共に emphasizes accompaniment or simultaneity, e.g. '友人と共に旅に出る' ('go on a trip with a friend') or '厳しいと共に優しい' ('kind as well as strict').

と共に and につれて are similar in that both can be translated as 'together with', but differ in nuance. と共に can express simultaneous actions or states, or the idea of accompaniment, e.g. '厳しいと共に優しい' ('kind as well as strict'). につれて highlights proportional change over time, e.g. '年を取るにつれて体力が落ちる' ('As I get older, my stamina declines').

と同時に and と共に can both mean 'together with' or 'at the same time as', but their nuance differs. と同時に emphasizes temporal simultaneity in neutral or factual contexts, while と共に often conveys shared action, emotional resonance, or development over time.

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.