～ため(に)— Purpose or Cause

• 留学するために、お金を貯めています。

  Ryuugaku suru tame ni, okane o tamete imasu.

  I'm saving money in order to study abroad.

  Volitional verb 留学する + ために = purpose ('in order to')

• 大雨のため、電車が止まった。

  Ooame no tame, densha ga tomatta.

  Due to the heavy rain, the trains stopped.

  Noun 大雨 + の + ため = cause ('because of')

• 事故があったために、道が渋滞している。

  Jiko ga atta tame ni, michi ga juutai shite iru.

  Because there was an accident, the road is congested.

  Past plain あった + ために = reason for the resulting situation

• ・Purpose reading needs a controllable/volitional verb before ために.
• ・Cause reading works with states, past events, or nouns (＋の) and often describes notable or formal reasons.
• ・Register: neutral to formal; the cause use is common in announcements.

Commonly confused with

The JLPT rarely asks whether you recognise a pattern — it asks which of several similar patterns fits. These are the ones ～ため(に) is tested against.

• ～あまり(に) — So Much That It Overwhelms
• ～おかげで — Thanks To
• ～せいで — Because Of (And I Blame It)
• ～せいか — Perhaps Because Of
• ～からといって — Just Because
• ～ことから — Judging From The Fact
• 次第だ／次第で — It All Depends
• だけあって — Living Up to It