You know Smith's TMS thought experiment "Were it possible that a human 
creature could grow up to manhood in some solitary place, without any 
communication with his own species, he could  ..." (110, see also 192).

In something I read I saw the author use an expression to criticize the 
thought experiment, a Latin expression, as I recall, that I believe 
meant that the posited thing is impossible.

I've been scouring electronic texts, searching on "grow up to manhood", 
etc., and I've read up on latin terms for philosophy, etc., but I can't 
come up with it.

Does anyone know the Latin term I mean, or the source that applies it to 
Smith's thought experiment?

Thanks,

/Dan Klein