"by reason that" 是一个正式的原因状语连词，意为“由于；因为；鉴于”，本质上等同于更常见的 "because" 或 "since"，但语气更正式、书面化，多用于法律文本、学术写作或正式文体中。
它的核心功能是引导原因状语从句，即后面需要接一个完整的句子（包含主语和谓语），说明事情的原因或理由。
通过例子更直观理解：
1、 He was not held responsible by reason that he was under 18 at the time of the accident.
（他没有被追究责任，因为事故发生时他未满18岁。）
2、 The contract was terminated by reason that the supplier failed to meet the quality standards.
（合同被终止，由于供应商未能达到质量标准。）
3、 She was granted an extension by reason that her mother was seriously ill.
（她获得了延期，鉴于她母亲重病在身。）
注意不要和同根短语 "by reason of" 混淆——
by reason that：后接从句（完整句子）；
by reason of：后接名词/名词短语（相当于 "due to" 或 "because of"）。
例如：
He missed the meeting by reason of illness.（他因病缺席会议。——后接名词 "illness"）
He missed the meeting by reason that he was ill.（他缺席会议，因为他生病了。——后接从句 "he was ill"）
"by reason that" 属于正式表达，口语中很少用（口语更常用 "because" "since" "as"），但在法律文件、合同、学术论文等正式语境中较常见。
总结："by reason that" = 正式版的 "because"，后接从句表原因。记住和 "by reason of"（后接名词）的区别即可正确使用～