On stackoverflow.com I found 3 instances of empiric solution and 4 instances of empirical solution.
What does this mean, if it means something—perhaps empiric and empirical are completely interchangeable? Or, does there exist some differences in usage?
Best Answer
As an adjective, empiric means empirical. It can additionally be used as a noun, while empirical cannot. So as long as you're using it as an adjective, then yes, empiric and empirical are interchangeable. (I think the -ical version usually sounds better, but that's just personal preference.)
Note that empiric was originally a noun only. The suffix -al was added to make it into the adjective empirical, but empiric itself came to be used as an adjective as well. Since this happened over four hundred years ago, and since both words have continued to be used with the same meaning, you can use whichever you like.
I should add, though, that empirical is more common in most contexts. (This probably has something to do with why I think it "usually sounds better", as I wrote above.)