看来有些同学对这两个词的用法并没有把握，没关系，如果你耐心点，花上十分钟看完本文，一定会信心十足。先来看看韦氏词典是如果说的：

Main Entry: importantly

Function: adverb

Date: 1611

1: in an important way

2: it is important that

usage

A number of commentators have objected to importantly as a sentence modifier (sense 2) and have recommended important instead. Actually both the adverb and the adjective are in reputable standard use in this function. Important is always used with more or most

--Merriam-Webster's Collegiate Dictionary, Eleventh Edition

再来看看美国传统字典对此是如何看的：

usage

Some critics have objected to the use of the phrase more importantly  in place of  more important  as a means of introducing an assertion,  as in More importantly, there is no party ready to step into the vacuum left by the Communists.  But both forms are widely used by reputable writers, and there is no obvious reason for preferring one or the other. In an earlier survey the introductory use of more importantly  was acceptable to half of the members of the Usage Panel.

寡人注：The Usage Panel is a group of nearly 200 prominent scholars, creative writers, journalists, diplomats, and others in occupations requiring mastery of language. The Panelists are surveyed annually to gauge the acceptability of particular usages and grammatical constructions. AHD的PANELISTS可参见

https://www.ahdictionary.com/word/usagepanel.html

另外， 我还查看了一些英国的词典，未发现以more/most important开头的用法，但有由more/most importantly 引导的例句。

More importantly， can he be trusted? (Oxford Advanced Learner’s Dictionary)

She has a pleasant personality, but more importantly, she is well qualified for the job.

If we served more soft drinks, there would be fewer hangovers and, more importantly, fewer drink-driving incidents. (Cambridge Dictionary)

Most importantly, you must keep a record of everything you do. (Longman Dictionary of Contemporary English)

由此可见，英国人在语言的运用上比美国人更严谨，保守，更能坚持语法规则，认同prescriptive grammar，而美国英语比较sloppy,更多的人赞同descriptive grammar是不难理解的。华盛顿州立大学的英语教授Paul Brians就是一个典型，像他这样的媚俗学者可能不少。语言在我看来，就像是一双布鞋，穿的人多了，必然越来越松。美国人太多了，而且很多移民其母语不是英语。以至于像“long time no see”这样的pidgin English也能被接受，许多黑人创造的英语更是当仁不让了。但即使在美国这样对语言不太讲究的国度，还是有不少愿意较真的人。请看哥伦比亚大学新闻学研究生院出版的期刊《哥伦比亚新闻评论》（注：The Columbia Journalism Review is an American magazine for professional journalists that has been published by the Columbia University Graduate School of Journalism since 1961）的编辑有关这个话题的评论。读完之后，你不难知道答案，到底那个更恰当一些。

Important/Importantly

Important ? Well, Interesting

By Evan Jenkins

Steve Parrott, associate director (later director) for university relations at the University of Iowa, e-mailed to ask, “Please consider a few words on ‘more important / more importantly.’ ”

Okay. Mr. Parrott had in mind sentences or clauses that begin with one of those phrases, like “Most importantly, the charges are tied directly to the original topic Mr. Starr was supposed to investigate.”

The short answer is that either form of the word is acceptable. Merriam-Webster’s Dictionary of English Usage (1994) has a lengthy and interesting (really) discussion of the longstanding argument (really) over important vs. importantly, with many citations, and concludes that “both are defensible grammatically and both are in respectable use.”

The tilt here, though, is toward “importantly.” The adverb can stand alone at the start of a sentence or clause — without “more” or “most” or any other modifier — and the adjective can’t.

Try it. Drop the “most” from the example quoted above; the sentence still works. Then, with “most” gone, drop the “ly” from “importantly”; the sentence no longer works.

(Some mindless aversion to “ly” adverbs at the start of a sentence — an extension of misguided rigidity about “importantly”? — must have been at work in the following sentence, since no human being ever spoke this way: “Not surprising, a variety of polls indicate...”)

The arguments for “most important” are strained, as an e-mail discussion with the freelance copy editor Christy Goldfinch of Fort Worth made clear.

“Important” commonly fails to modify any specific part of its sentence, so the adjective advocates contend that it can be understood to modify the whole thing — a “sentence adjective.” Well, “importantly” can certainly be called a “sentence adverb.”

But with “importantly” there’s no need for that dance. The adverb has an element to grab hold of within its sentence, the verb or the overall predicate. (And that, quite apart from any “sentence adverb” justification, makes the literalists’ objection to “hopefully” at the start of a sentence fallacious, as well as outmoded.)

Another argument for “most important” is that the phrase “What is” is understood to precede it. If that were a natural supposition, all sorts of adjectives (with modifiers) could start sentences. But “Most happy, the storm ended,” just doesn’t make it.

The “most” approach is acceptable (not preferable) with the one adjective “important” not on logical grounds but because it is widely used and well established. And in passages that start with modifiers ending in “ly” — “equally” comes to mind — using “important” is handy.

P.S.: Nothing in this sermon should be construed as enthusiasm for “Firstly...,” an irritating start for an even more irritating series.

CJR

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All content © Copyright 2008 Columbia Journalism Review at Columbia University's Graduate School of Journalism.

https://archives.cjr.org/resources/lc/important.php

最后，对想在英语语言文化上有点追求，有点讲究的朋友，或者想成为一名wordsmith的人，不妨多读一些英文报纸，勤翻字典，或浏览网上词典—几乎所有主要的英文词典都提供免费在线服务。在线词典比纸质的好在可以听词的发音，有更多的例句，而且有一些Word Game，vocabulary test,以及有关词的用法，历史，演化等的故事。比如这个：

Usage Notes

Is This Cat 'Uninterested' or 'Disinterested'?

https://www.merriam-webster.com/words-at-play/uninterested-or-disinterested

牛津字典、韦氏大学词典、剑桥词典，朗文词典，及美国传统字典是我最最喜欢的几本字典，质量非常高。