Doubtlessly, + clause
置于句首并用逗号隔开，表示说话人对整个句子的判断十分肯定，语气偏正式。
Doubtlessly, she will be the first to arrive.
毫无疑问，她会第一个到。
无疑地；确定地
毫无疑问地,肯定地；毫无疑问
毫无疑问地,肯定地
without doubt; certainly
She doubtlessly knows the answer to that question.
她毫无疑问知道那个问题的答案。
用法提示：此处 doubtlessly 作副词，修饰动词 knows，表示‘毫无疑问地’。
This painting is doubtlessly one of his finest works.
这幅画毫无疑问是他最杰出的作品之一。
用法提示：doubtlessly 修饰整个句子，表达对陈述的肯定程度。
The team will doubtlessly win the championship this year.
这支队伍今年毫无疑问会赢得冠军。
用法提示：doubtlessly 置于助动词 will 之前，强调对未来事件的确定性。
置于句首并用逗号隔开，表示说话人对整个句子的判断十分肯定，语气偏正式。
Doubtlessly, she will be the first to arrive.
毫无疑问，她会第一个到。
放在情态动词或助动词之后、主要动词之前，是副词最常见的位置。
This discovery will doubtlessly change the whole field.
这一发现无疑会改变整个领域。
用于系动词之后、形容词之前，修饰表语，强调判断确凿无误。
The results are doubtlessly accurate.
这些结果无疑是准确的。
grammar · medium
易错句子There is no doubtlessly that he will pass the exam.
正确表达There is no doubt that he will pass the exam.
“no doubt”是固定名词短语，意为“毫无疑问”；doubtlessly 是副词，不能紧跟在 no 后作名词中心词。改为 no doubt 后语法正确且保留原意。
grammar · medium
易错句子She looked at the letter doubtlessly, not knowing what to do.
正确表达She looked at the letter doubtfully, not knowing what to do.
doubtlessly 表示“毫无疑问地”，而这里描述因不知道该怎么办而看信的神态，应是“心存疑惑地”，须用 doubtfully；两词意义相反，不能混用。
grammar · medium
易错句子It is doubtlessly that the plan will succeed.
正确表达It is doubtless that the plan will succeed.
系动词 is 后需要形容词作表语，doubtless 可作形容词表示“确定的”；doubtlessly 是副词，不能单独放在 is 后构成“It is ... that”结构。
与 doubtlessly 意思几乎相同，都表示“毫无怀疑地”，但 undoubtedly 是现代英语中最常用的说法，适用于口语和正式书面语；doubtlessly 罕见、偏书面甚至显得陈旧，日常表达中应优先用 undoubtedly。
doubtless 既能作副词（Doubtless he will agree.），也能作形容词（较罕见），而 doubtlessly 只能作副词；作副词时 doubtless 更常见，且常弱化为“大概、想必”的推测语气，肯定程度不如 doubtlessly 强。
两者只差一个字母，但态度相反：doubtfully 指“带着怀疑、不确定”，doubtlessly 指“毫不怀疑、肯定”。描述某人以怀疑态度做某事时用 doubtfully，绝不能用 doubtlessly。
doubt（词根）
doubt + -ful
doubt + -less
un- + doubt + -ed + -ly
doubt + -er
self- + doubt
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