ために

The structure ために has two major uses: expressing purpose ("in order to," "for the sake of") and expressing cause/reason ("because of," "due to"). Understanding which meaning is intended depends on the form of the word before ために and the context.

Purpose – "in order to," "for the sake of"

When expressing purpose, ために follows a verb in the dictionary (non-past) form or a noun + の. The subject of both clauses is typically the same, and the main clause describes a volitional action – something the speaker deliberately does to achieve the goal.

The verb before ために must be in the dictionary form (not past tense) when expressing purpose. If you see a past-tense verb before ために, it signals a cause/reason reading instead.

Cause/Reason – "because of," "due to"

When expressing cause or reason, ために can follow a verb in any plain form (including past tense), a noun + の, an い-adjective, or a な-adjective + な. Unlike the purpose usage, the subjects of the two clauses can be different, and the result in the main clause is often unintentional or beyond the speaker's control.

The cause/reason usage tends to appear more in written or formal contexts. In casual spoken Japanese, から or ので are more common for expressing reasons.

How to distinguish the two meanings

A few clues help determine which meaning is intended:

• Past-tense verb before ために → cause/reason
• Dictionary-form verb + intentional action in the main clause → purpose
• Negative or uncontrollable result in the main clause → cause/reason
• Noun + のために can be either, depending on context:
  けんこう健康のために、やさい野菜をたべている食べている。

  I eat vegetables for (the sake of) my health.
  びょうき病気のために、しごと仕事をやすんだ休んだ。

  I was absent from work because of illness.