What is the difference between なぜなら、だから、and なので？

Question

I'm trying to get clarification on how to use these three pieces of grammar and whether or not they all hold some kind of "Because" meaning.

Answer 1

They can be used to express the entailment B → A, but they are syntactically different.

Conjunctions

• から 'because'. Attaches to an indicative from of a clause. Can appear in a focus position.

  B から A。
  'A because B'

  A のは B からだ。
  'It is because B that A'

• ので 'because'. Attaches to the attributive form of a clause. Cannot appear in a focus position.

  　B ので A。
  　'A because B'

  × A のは B のでだ。
  　'It is because B that A'

Adverbials

• なぜなら 'that is because'. Initiates a sentece, and concords with からだ.

  A。なぜなら、B からだ。
  A. That is because B.

• だから, なので (colloquial) 'therefore'. Initiates a sentence.

  B。だから/なので、A。
  B. Therefore, A.

I feel that there is a subtle difference in meaning. The following may not be strictly followed, but is a tendency that I think holds.

• conjunction から, adverbial なので tend to be used for subjective/humane reasoning.

  あのラーメン屋は人を待たせるから、行かないことにした。
  あのラーメン屋は人を待たせる。なので、行かないことにした。
  'Since that ramen shop makes the customer wait, I decided (from my own will) that I will not go there anymore.'

• conjunction ので, adverbial なぜなら, だから tend to be used for objective/logical reasoning.

  あのラーメン屋は人を待たせるので、行かないことにした。
  あのラーメン屋は人を待たせる。だから、行かないことにした。
  'That ramen shop makes the customer wait. Therefore, it follows that I decide that I will not go there anymore.'

Answer 2

なぜなら(ば) is used in formal written Japanese. It brings strong focus on the reason.

X。なぜなら、Y。("Y is the reason for X")

It can be paraphrased using から or ので (can be used in both spoken and written Japanese):

YからX。

YのでX。

The difference between から and ので is that ので indicates objective causality. This means that ので cannot be used for a command, request, suggestion, invitation or opinion.

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The だ in だから:

It's used when it is in sentence-initial position. Or when a noun precedes から and is expressed as a cause rather than a place of origin.

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The な in なので:

It's the attributive form that allows nouns to be connected.

[Noun]だ

[Noun]なので

[Noun]だので (Incorrect)