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Any detailed meaning of using 'OF' in the beginning of this sentence? Or we actually can substitute 'OF' for other articles without changing any details?

Thanks in advance!


It's literally the same as saying "The sinoatrial (SA) node is of critical importance." However, by constructing it as originally written, the writer alerts the reader that the upcoming subject of the sentence (the SA node) is worth paying attention to, bringing enhanced attention to it rather than pointing out its importance afterward.


For one, "of" is not an article. Replacing it with one here (such as "the") would be incorrect. The preposition "of" marks the genitive case, and essentially serves to turn the noun phrase "critical importance" into a sort of adjective. I.e., "of critical importance" is semantically identical to "critically important." The only difference, other than a stylistic one, is that "of critical importance" sounds natural coming before that which it describes, whereas "critically important" would sound rather artificial:

"Critically important is the sinoatrial node" is not wrong, grammatically speaking — it's just unnatural and awkward. Instead one would always say, "The sinoatrial node is critically important." This is contrasted with "of critical importance," where I feel it is equally acceptable to say both "Of critical importance is the sinoatrial node," and "The sinoatrial node is of critical importance."

Some other examples of using a genitive noun phrase to function as an adjective:

  • "Of note" = noteworthy
  • "Of interest" = interesting

There may be a slight difference in formality (using of could be perceived as more formal) is certain circumstances.

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