Over the past week, I ran a non-scientific poll on my recently-launched, writing-themed Twitter page to determine what my Twitter followers thought was the proper plural form of the singular “encyclopedia” or “encyclopaedia”, and here are the final results of the poll:
With a total of 13 votes cast, seven votes were cast for “encyclopedias”, three votes were cast for “encyclopediae”, two votes were cast for “encyclopaediae”, and one vote was cast for “encyclopaedias”. Ten votes were cast for either “encyclopedias” or “encyclopediae”, and three votes were cast for either “encycopaedias” or “encyclopaediae”, which indicates a majority preference for plurals based on the “-pedia”-suffixed form of the singular “encyclop(a)edia” over the “-paedia”-suffixed form. Eight votes were cast for either “encyclopedias” or “encyclopaedias”, and five votes were cast for either “encyclopediae” or “encyclopaediae”, which indicates a majority preference for the “-s”-suffixed plural over the “-e”-suffixed plural.
I prefer to use “encyclopedia” in the singular. However, I do not regard “encyclopaedia” to be a misspelling, as I regard “encyclopaedia” as a valid alternate spelling of the same word. I almost never use “encyclopaedia”, except when I need to acknowledge that there are multiple acceptable spellings of “encyclop(a)edia”, such as this blog post or the poll that I ran on Twitter. Usage of “encyclopedia” is commonplace in American English, but some other English dialects may use “encyclopaedia” as the common spelling.
Regarding whether I prefer to use the “-s”-suffixed plural or the “-e”-suffixed plural of “encyclopedia”, I regard the “-e”-suffixed plural to be more formal than the “-s”-suffixed plural. I will generally only use “encyclopediae” as the plural form of “encyclopedia” to express formality within formal writing, otherwise, I use “encyclopedias” in the plural.