I was talking with a random guy on the street, somewhere in Asia. English was clearly his second language, though my Mandarin clearly had no comparison to his English. He didn't speak Mandarin, though. Things got interesting when he used the word "oftenly".
"I skate oftenly," he said.
Technically, oftenly is not usually a word, but technically it is, but technically it's the wrong word. The word he meant to use was "frequently". If he wanted to say that he skated from time to time, specifically times that are so frequent that they "occur oftenly" (proper usage because the verb occur is about time), it would have been proper to say, "I skate often."
What's the difference and who cares, anyway!?
English speakers love to argue about grammatical distinctions that clearly provide no further clarity—and may even be right—or even wrong and right differently—and to make such arguments about these clearly unclear differences about right and wrong usage differently, even though they have nothing to do with the difference between right and wrong. And, I still have no idea why.
I even asked my friend whether in his country they liked to argue about nothing as much as English speakers did. Absolutely not! It was almost as comical for him to observe me deliberating with myself about the difference between "often" and "oftenly" as it is for a Brit to watch Monte Python banter about British nothingness—notwithstanding that it is most entertaining to watch the Brit be entertained by the bantering banterer, but I digress.
How should we ever know that we ought use the -ly suffixed adverb "frequently" and the non-suffixed "often" interchangeably in the same sentence? It all comes down to English style guide preferences.
In typical, classroom, American English, words like "tomorrow" and "yesterday" are considered adverbs. This may seem strange—and I do think it is strange indeed. Usually, adverbs describe manner or the way in which a verb is acted out.
Consider "eating". "I eat quickly." This makes sense with the adverb "quickly" as the eating is done in a quick manner. But, if I will eat "tomorrow", is the manner in which I will eat described with any more clarity? Does the word "tomorrow" really behave like an adverb?
As with "tomorrow", even if I eat multiple times everyday, "often" just doesn't seem to describe the manner of eating as much it describes the days and times when I eat; but "frequenly" does describe some of the manner. And, that brings me to Cambridge.
Cambridge has a different take than Amercia's 20th century classroom; "yesterday" and "tomorrow" are not adverbs—they are pronouns.
From the English style viewpoint of Cambridge, words like "tomorrow" don't tell one ounce about the manner and speed with which a verb is acted out. Rather, "tomorrow" represents a day as much as "me" represents myself, Jesse Steele, the writer of this ridiculously multi-topicked article with a grammatically incorrect title.
Now, I must add my own two cents about understanding grammar. By "tomorrow" being a pronoun, saying, "I will eat tomorrow," doesn't mean that I plan to eat the actual day of Thursday should I happen to be speaking on a Wednesday. In this "case", the pronoun "tomorrow" would have the "Locative Case" usage of "place in time", but that is a discussion—and an argument in favor—of grammatical noun case applicability to English. And, though I don't want to keep digressing, if using the Cambridge style, it does help to clarify the usage of "tomorrow" by identifying its functional "noun case" and while classifying it as a "modifier noun". If that doesn't make sense, that's okay, it's only two cents.
Where was I?—tomorrow!
If we view "tomorrow" and "yesterday" and words of the like as pronouns that represent days, then we would easily know that "often" is also a pronoun for time—whether time of day or any given day or month, year, et cetera. And, we already know that pronouns do not receive the adverbial suffix, -ly. "Often" should be considered a pronoun, just as "tomorrow", "today", "yesterday", and "everyday" for that matter.
Now I'm wondering, with the Cambridge style, if I were to describe an activity whose manner is best described as done in a "tomorrow" -like manner, would I say that I, "do it tomorrowly."? I think the best answer would be, if you can't save an adverb's life, it's more merciful to kill it quickly. After all, in any well-described writing, adverbs would be a redundancy, which is another argument in favor of Cambridge—"tomorrow" isn't an adverb, so there's nothing wrong with using it. But, I digress yet again.
In conclusion, we understand that the Cambridge style for English usage helps us to clear up this "often" problem. Proper usage is, "I skate frequently and often," because "frequently" is an adverb while "often", like "tomorrow", is a pronoun.
Needless to say, my friend was quite amused at the remarkable time English speakers have with which to dedicate concern about use of language. But, it is likely that he will "frequently and often" use the word "often" properly and correctly in the future. Thank you Cambridge.