A few weeks ago, I noticed that a first-year student of mine used the word "conclusory" instead of "conclusive." I corrected him -- I was polite (I think), but my job is to teach students and part of the job is to teach them how to use words properly. A "conclusory argument," I pointed out, is an argument that is long on conclusions and short on supporting evidence; "conclusive evidence," on the other hand, is evidence that points persuasively to a certain conclusion.
To my surprise, a week later I read this Language Log item, written by linguistics professor Mark Liberman:
A few days ago, when Senator Arlen Specter was asked about Attorney General Alberto Gonzales' statement on the U.S. Attorney firings, he dismissed it as "conclusory". This usage puzzled me; it's missing from the standard (non-legal) dictionaries; and it was also news to Steve of the Language Hat blog, who must surely be in the top thousandth of a percentile or so in knowledge of English vocabulary.
Huh? What do you mean, missing from standard English dictionaries? Well, sure enough, here's the entry from the Oxford English Dictionary: "Relating or tending to a conclusion; conclusive." And from the Random House, by way of dictionary.com, "conclusive."
Shocking as it is to me -- and to several lawyers that I talked to -- but "conclusory," which I'd long assumed was a standard English term with the definition I just gave, is actually legalese. We lawyers are just so steeped in legalese that there's some legalese we no longer recognize as anything but normal.
In any event, my instructions to my class were correct: In legal discourse, "conclusory" indeed means something very different than "conclusive." But of course it makes sense that the student didn't grasp this; he hasn't yet become acculturated to legal lingo the way I have.