This is a list of common frequency adverbs in English with rough estimates of their absolute frequency someone has posted on an ESL study site:
Always (100% of the time)
Frequently (about 90% of the time)
Usually (about 80% of the time)
Often (about 70% of the time)
Sometimes (about 50% of the time)
Occasionally (about 40% of the time)
Seldom (about 20% of the time)
Rarely (about 10% of the time)
Never (zero percent of the time)
Clearly, the usage of "never" (0%) and "always" (100%) as it relates to an absolute frequency would never be in question, but it is unclear if it is possible to say a given usage of a frequency adverb was correct if the exact absolute frequency or range of frequencies it represents were known.
For example, take the word "sometimes" - how would you know that 20% or 80% "of the time" would be a poor usage of the term, but 50% would be okay? Clearly, statically speaking there is a huge difference between 20% and 80% of the time, but it is unclear how a given frequency adverb's usage with an absolute frequency or frequency range would be accessed to be appropriate, or for that matter, inappropriate.
Is it ever possible to prove that the usage of frequency adverb is valid or invalid based on knowing the absolute frequency or range of frequencies it represents, and if so, how? Which is to say, is it possible to assign a range of frequencies to a frequency adverb and know they're correct, and if so, how?
If so, is the list referenced above correct, and if not, why?