The word ため (also written with kanji as 為(ため)) is a noun that often means 'for the benefit/sake of'. In Japanese grammar, it is considered a non-independent word, which means it cannot stand alone and must always be preceded by another phrase. When the case marking particle に follows ため, it usually indicates that the preceding phrase (A) is the objective or purpose for which an action is performed.

Conversely, when ために follows a verb in its past tense, its meaning shifts to indicate a cause or reason, translating as 'due to (A)' or 'because of (A)'. A good way to think about ため in general is as 'on account of (A)'. This single interpretation works for both meanings, by showing that (A) is the main reason or circumstance that brought about the result (B).

To use ために to express a cause or reason like 'on account of', 'as a result of', or 'because of', you can attach it directly to the past form of a verb, or to a noun using the particle の. It can also follow い-Adjectives and な-Adjectives when they are in their attributive form.

• 昨日(きのう)の夜(よる)、窓(まど)を開(あ)けたまま寝(ね)てしまったために、風邪(かぜ)をひきました。
  Because I fell asleep last night with the window open, I caught a cold.
• 音(おと)がうるさいために、宿題(しゅくだい)に集中(しゅうちゅう)できませんでした。
  Due to the loud noise, I couldn't concentrate on my homework.
• この辺(あた)りは静(しず)かなために、お年寄(としよ)りが多(おお)く住(す)んでいます。
  Because this area is quiet, many elderly people live here.
• 交通(こうつう)事故(じこ)のため、電車(でんしゃ)が遅(おく)れています。
  Due to a traffic accident, the train is running late.

This 'on account of (A)' idea can apply to events that have already occurred (as seen in the examples above), as well as to future goals that motivate an action (as covered in our other grammar point on ために).

• 留学(りゅうがく)するために、毎日(まいにち)日本語(にほんご)を勉強(べんきょう)しています。
  In order to study abroad, I'm studying Japanese every day.
• 昨日(きのう)は朝(あさ)まで勉強(べんきょう)していたため、今日(きょう)の授業(じゅぎょう)は眠(ねむ)かったです。
  Because I was studying until morning yesterday, I was sleepy during class today.