My gut tells me “investable” with “a” because the definition depends on how much you are able to invest.
The case for “investable” over “investible”
- Merriam Webster’s Collegiate Dictionary includes “investable,” but not the alternative spelling.
- Garner’s Modern American Usage calls “-ible” “dead as a combining form in English,” while “-able” is a living suffix that may be added to virtually any verb without an established suffix.” It includes “investable” among “some of the hundreds of adjectives preferably spelled -able.”
The case for “investible” over “investable”
- Google turns up about 393,000 references to”investible” vs. only 320,000 to “investable.”
- Fowler’s Modern English Usage says “The –ible form is the natural one for words derived from Latin verbs ending –ere or –ire, making adjectives in –ibilis.” I don’t know about “making adjectives in –ibilis,” but lo and behold, my dictionary says the word “invest” comes from the Latin investire. However, my copy of Fowler’s dates back to the 1960s.
- The Financial Times Lexicon goes with “investible.” Could this be a British thing?
The SEC is a draw
A search of the SEC website yielded an equal number of results for both spellings. I wonder if they use both as key words for search purposes.
Note: I updated this blog post in 2015 to delete an outdated reference to an inactive poll.