５課

"ためだ" and "ために" are used to express purpose, reason, or cause. The phrase "ためだ" is generally used to state the reason or purpose, while "ために" is more commonly used to indicate that an action is done with a particular goal in mind or that something happened due to a particular reason.

"によって" is used to indicate a cause, method, means, or variation depending on context. "による" is the attributive (modifying) form of "によって" and functions to modify nouns in Japanese.

Both から and ことから are used to indicate a reason or cause in Japanese, but they differ in nuance and formality.

Both おかげで and せいで are used to indicate the cause of an outcome in Japanese, but they carry different nuances. おかげで implies a positive outcome or a feeling of gratitude, while せいで indicates a negative or undesirable outcome, often assigning blame.

"のだから" (のだから) is used to emphasize a reason or justify a statement based on an obvious or known fact.