Having to finish his homework,the boy needs a pen..这里的不定式是充当原因状语还是目的状语？

the boy needs a pen to finish his homework。。这句的话，我就知道不定式是充当目的状语。。求助大神。

好奇怪的句子。
为什么不直接写成To finish his homework,the boy needs a pen.才是最地道的表达啊
口语中也常用。由此可看，是原因状语。

目的状语。。

to finish his homework 目的状语

你好！ 好奇怪的句子。 为什么不直接写成To finish his homework,the boy needs a pen.才是最地道的表达啊 口语中也常用。由此可看，是原因状语。 仅代表个人观点，不喜勿喷，谢谢。