I came across a sentence on Grammarist:
Amongst is unquestioned in British English, where it appears about once for every 18 instances of among.
Why is for used here? Can it be omitted as follows?
Amongst is unquestioned in British English, where it appears about once every 18 instances of among.
I have heard such phrases as "once every two years". Is it grammatical to say "once in every two years"?
No, you cannot drop the "for." It indicates that there is a ratio between instances of among and instances of amongst. There is one instance of "amongst" for every eighteen instances of "among." When you drop the "for," it makes it sound as though one of the 18 "among"s is actually an amongst. Because the units being compared are both independent, the sentence requires a word like "for" or "per."
Generally when we talk about things happening over time, time is the independent unit, while the other variable is dependent. In English, we frequently drop the prepositions for time, ("once per day" becomes "once a day," "twice per month" becomes "twice a month"). A notable exception would be a phrase like "once in a blue moon."
I like Katy’s answer very much. Being a somewhat literal-minded person, I would consider the two phrases when written to be literal.
When including the word “for” the phrase sounds like a ratio or average. Out of a group of sets where every set contains 18, an instance happens an average of once. But, you can not predict which item is the once. Or, if all the sets have the same number of instances. Or, if you redistribute or change the way you count the items in the sets, that each set will contain the same number of instances. It is an average ratio.
However, when you omit the word “for”, the phrase sounds like the instance is more predictable and constant. For example, the instance always happens on the first item, or always happens on the last item.
When you speak the phrases instead of writing them, they are usually more informal. Therefore, they can both mean the same thing.
