次第(しだい)だDepending on, So

Both can be translated as according to, but differ in nuance. に応じて emphasizes adapting or responding flexibly, as in 年齢に応じて料金が変わる (The fee changes according to age). 次第だ・次第で stresses that the outcome is directly determined by another factor, as in 成功するかどうかは準備次第である (Success depends on preparation).

にかかっている expresses strong dependence, implying that the outcome rests entirely on something, as in 成功は君にかかっている (Success depends on you). 次第だ・次第で also conveys dependence, but less emphatically, and 次第で can modify the following phrase, as in 調査の結果次第で方針を決める (We will decide the policy based on the results of the investigation).

Both expressions mean 'depending on' and can be used in similar contexts. For example, 実験の結果の如何で研究資金が決まる ('Depending on the results of the experiment, funding will be decided.') can be rephrased as 実験の結果次第で～ with no change in meaning. Note, however, that 次第 always attaches directly to nouns, while 如何 can connect either directly or with の. Also, 如何 is used in certain set expressions like ～の如何を問わず 'without considering' where 次第 is typically not used.

Both of these expressions use 次第 but differ slightly in usage. 次第 alone attaches to verb stems to emphasize timing or sequencing, expressing that one action is a condition for the next. For example, 終わり次第連絡します ('I'll contact you as soon as I'm finished'). 次第だ・次第で, by contrast, introduces conditional relationships or dependence. For example, 努力次第で結果は変わる ('The results will depend on your effort').

The grammar point 次第だ／次第で is used to indicate that a situation or course of action depends on something specified, often involving uncontrollable events or conditions. On the other hand, 〜かは〜によって違う expresses that the result or state changes depending on certain conditions or variables, focusing on how outcomes differ based on those factors.