false reasoning, vicious reasoning, circular reasoning; petitio principii [Lat.], ignoratio elenchi [Lat.]; post hoc ergo propter hoc [Lat.]; non sequitur, ignotum per ignotius

It would therefore be an ignoratio elenchi to allow oneself to be disposed of in such a manner.

Why does he immediately add that for the pluralist to plead the non-mutation of such abstractions would be an ignoratio elenchi?

They were cautioned or ridiculed as the case might be, on the score of "confusion of thought" and "inaccuracy of mind"; they were convicted of great logical sins, ignoratio elenchi, or undistributed middle terms; and bold theories began to make their appearance about religious principles and teaching, which did not easily accommodate themselves to popular conceptions.