"know your enemy"
and
"people are greedy and stupid"
I see two possibilities for the first phrase:
Nosce hostem tuum and
Nosce inimicum tuum. The first is better if you are talking about an enemy in the military sense, the second if you are talking about a personal enemy.
The format for the second is fairly straightforward:
Populus est X et Y; the question now is what to put for X - "greedy" and Y - "stupid", as there are numerous choices; I'll summarize my own feelings on the various words below:
Greedy:
cupidus (more like "desirous, eager"; I would not recommend this one),
avidus (more like "avid" or "ardent" in the lustful sense; I don't think this is right either),
avarus (more like "stingy, covetous", cf. the English cognate "avarice"),
edax (more like "rapacious, consuming"). I think the last two are the only plausible choices here, and it depends on whether you want to emphasize the selfishness of greed (use
avarus) or its belligerence (use
edax).
Stupid:
Stultus is the first word that popped in my mind, but
ignarus (more like "unaware") and
inscitus (more like "uninformed, unskilled") are possibilities.
Imprudens, which emphasized foolishness, is another possibility.
My final verdict:
Populus est avarus et stultus, mainly because even a person who knows no Latin might puzzle this one out from English cognates.
I welcome other thoughts on this one...
