`` 'since, because' attaches to a clause, whereas `` 'with (the reason being)' attaches to a noun. `` is an indicative clause (ordinary sentence), so you can simply attach ``, but not ``.
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In order to use ``, you have to have a noun. To do that, you use the formal noun (or nominalizer) `` taking an appositive clause. In appositive clauses and relative clauses, na-adjectives take the adnominal ending ``.
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