Latin: If You Don't Know It, Don't 'Throw' It
Some of us like to pepper our prose with foreign expressions. No harm in that, provided one does not overdo it. But in an attempt to appear erudite, one must be careful not to appear foolish.
We have all heard about ad hominem arguments. They come in two flavors, well described here. Some of the politically correct persuasion, however, want to speak of ad feminem arguments. But this is bad Latin based on a failure to realize that, while homo is third declension masculine, femina is first declension feminine. Correct is ad feminam.
I came across a blogger who invented a fallacy he named ab hominem, from the man. But whereas ad (like post) takes the accusative case, ab (like ex) takes the ablative. One cannot therefore just slap ab up against hominem on the model of the juxtaposition of ad and hominem. Homo has to be be put in the ablative singular. Correct is ab homine. Another blogger (or was it the same guy?) excogitated an around the man fallacy, calling it peri hominem. But peri is Greek; so perish that monstrosity.
Another vexatious matter is the insertion of a Latin nominative in a non-nominative position in an English sentence. Suppose you know that ens realissimum means most real being, and that ens summum means highest being. These expressions are nominative singular. What you want to say, using the Latin expressions, is that the concept of the most real being is the concept of the highest being. To be persnickety about it, one cannot write: The concept of the ens realissimum is the concept of the ens summus. One ought to write: The concept of the entis realissimi is the concept of the entis summi.
DISCLAIMER: My knowledge of Latin is limited and my knowledge of Greek consists of little more than knowledge of one hundred or so Greek philosophical terms. Address all questions about Latin and Greek to Dr. Gilleland, my colleague in the Classics Department of the Free University of the Blogosphere. If I have made a mistake in the foregoing, he will be sure to correct me. This is what we call blogospheric quality control.