Populus.
It saddens me that this is necessary. It wasn't long ago that Latin was part of the standard curriculum in grammar schools.
The people
For clarity: This is my answer, not the answer given by Plato (who argues that the guardians should guard themselves) or answer from Juvenal (who implicitly takes the position that this is an impossible problem).
Because studying Latin helps people learn about the grammatical structures which they use in their native tongue without understanding.
Because understanding Latin makes it much easier to learn any of the many Latin-influenced languages, or even to guess at what text means without knowing the language.
Because knowing Latin is a prerequisite for learning much of European history from primary sources.
How? Is there something magical about Latin? Would other, less dead languages have the same effect?
> Because studying Latin helps people learn about the grammatical structures which they use in their native tongue without understanding.
That's hardly unique to Latin.
> Because understanding Latin makes it much easier to learn any of the many Latin-influenced languages, or even to guess at what text means without knowing the language.
Why not learn another Latin-derived modern language, instead? You get some of that same effect, and you learn a language that isn't dead.
> Because knowing Latin is a prerequisite for learning much of European history from primary sources.
How many people are going to want to do that, ever? Consider the opportunity cost of learning Latin for those who won't. And then, of the people who will want to read those primary sources, how many of them would benefit from being able to read them in Latin rather than in a translation?
It would be much more helpful just to study those grammatical structures directly in the native tongue. Studying the grammar of your own language via latin is just an odd way of doing it. English and latin are not very similar grammatically.
[citation needed]
Really, there has been experimental research on this subject, and the best considered conclusion is that Latin doesn't have any particular virtue in training the mind in logical thought.
Note (as anyone who reads my HN profile will see) that I by no means disparage the study of foreign languages, dead or alive.
Ideas are expressed differently in different languages and there are often important nuances, where the real message is to be found, which are lost. For instance, it might have more of the intended effect to translate it as: "Who is watching the watchers?". A little paranoia here or there... today, the idea of 'guards' is pretty benign.
That Latin is a foundational language for most of the West is also an important consideration. It enables people to understand written or verbal communications which use words they haven't encountered before... Something like being able to understand a programming language you've never written in by virtue of its apparent syntax and flow control. A good illustration might be the use of "for".. you have for each, for x in y, or for(;;). Knowing the "root", "for", pretty much explains how to decode the ()'s contents in the lesser English-like C style.
Thirdly, there are many great ideas written in Latin. Those ideas have profound things to say and we risk cutting ourselves off, as a people, or maybe more importantly as individuals, from "lessons learned".
If you're going for linguistic diversity, why not go all-out and learn something completely unrelated to Latin? Maybe one of the Asian languages, for example. I know one guy who says he thinks differently when he speaks Mandarin than he does when he speaks English. Maybe that would be a little too hard, compared to Latin?
> Thirdly, there are many great ideas written in Latin. Those ideas have profound things to say and we risk cutting ourselves off, as a people, or maybe more importantly as individuals, from "lessons learned".
Surely we, as a people, can afford a few decent translators?
Understanding even only the rudiments of Latin will give you tremendous insight in to the historical development of languages and will help you a lot in learning them as spoken today.
Perhaps I should have posted a link to the Wikipedia article instead. http://en.wikipedia.org/wiki/Quis_custodiet_ipsos_custodes
[edit: added first two sentences]