In an answer on another question, @TsuyoshiIto wrote:
[U]nlike commas in English, 読点 in Japanese is rarely (if ever) grammatically required. Authors are free to use 読点 wherever they feel that it makes sense to make a pause when pronounced.
And in a comment on yet another question, @dainichi wrote:
I think [こわいだから] might exist in some dialects, but in standard Japanese, it is ungrammatical regardless of formality. Unless it's こわい、だから[...] which is something else. (emphasis added)
What is this "something else?" According to answers on two other questions (this one and this one),
だから is simply
だ + から. Therefore, I would expect
*こわいだから to be ungrammatical because
*こわいだ is ungrammatical. In fact, I would expect
だから to only follow things that
だ can follow.
However, I'm having trouble reconciling what @dainichi and @TsuyoshiIto wrote. If
*こわいだから is ungrammatical, and 読点 aren't required, how can
こわい、だから be grammatical?
Perhaps my confusion stems from the difference between these forms:
だから be explained as
だ + から in all three cases? If so, does that mean
だ can begin a sentence or clause, or is
だから somehow special? What is the "something else" referred to by @dainichi?
In short: how can I make sense of this?