Once upon a time I misformed the gerund of studeō by writing ad studiendum [sic]. It seemed natural, and I even began to second-guess myself: is this a 2nd conjugation verb (studeō, studēre)? Maybe I've misremembered and it's 3rd-iō (studiō, studere [sic]). But that just couldn't be the case. So why did I make the mistake?
I've since seen the same error in the latest edition of John Traupman's venerable and handy New College Latin Dictionary. In the English-Latin section, under 'study period' (i.e., 'study hall') you'll find spatium ad studiendum [sic].
So why did he and I make this mistake? We're joined by many others, both on the web and in manuscripts dating to at least the 14th century.
I can only guess that it's from the -i- in studium. Is the noun more common than the verb? Any similar errors committed by readers?
Possibly related:
