"Short" and "brief" are synonyms; an event that is "short" or "brief" occurs for a short period of time. Yet "shortly" and "briefly" are not synonyms; an event that shall occur "shortly" shall occur in a short time, while an event that shall occur briefly shall occur for a brief period of time.
The meaning of "briefly" follows the normal rule for forming adverbs from adjectives, but the meaning of "shortly" does not. That is:
- If I stare lecherously, that means my staring is lecherous
- If I devour greedily, that means my devouring is greedy
- If a building collapses spectacularly, that means its collapsing is spectacular
- If I will visit briefly, that means my visiting will be brief, BUT...
- If I will visit shortly, that does NOT mean my visiting will be short, which breaks the pattern
How, and when, did this puzzling state of affairs come to be? It's not even as though English lacks other words to express the meaning "shortly" has - we have the perfectly good words "soon" and "imminently", after all - so how and why did people ever even begin to use "shortly" in this seemingly illogical manner?