Christophe Grandsire-Koevoets wrote:
> 2010/1/21 R A Brown <[log in to unmask]>
>> The ancients did better. The imperative clearly distinguished imperfective
>> ('present imperative), perfective imperative ('aorist imperative') and
>> perfect imperative ('perfect imperative' [rarer than the other two]).
> Well, Modern Greek still does (although I've never seen a perfect
> imperative, it's possible, since έχω does have an imperative έχε). 

Perfect imperatives are not common in the ancient language 
and occur mostly in the 3rd person form. Unlike modern 
Greek, the ancient language had imperative endings for both 
2nd & 3rd person (the 1st plural "Let's ....." was expressed 
by subjunctive forms).

The 3rd person perfect imperative is almost always passive 
and expresses a command that something just done or about to 
be done shall be _decisive and final_. Two examples (literal 
translation followed by paraphrase):

Let so much have been thus said
i.e. Let what has been said be sufficient

Let this have been said by way of introduction
i.e. Let this be the final word concerning introduction

This usage is found in mathematical writing, implying that 
something proved is proved _once and for all_ or that lines 
or points fixed are to remain as data in a following 
demonstration. For example, when Euclid wrote: "let any 
point D be assumed as taken in the line AB, and equal to AE 
as cut off from AC", he in fact used the perfect passive 
imperative of the verb 'to take' where English had "let ... 
be assumed to to taken" (he also, of course, used Α Β Γ Δ, 
not A B C D    :)

The second person is rare, but again stresses finality. For 
example in Democritus we find _pepauso_ - literally "Have 
stopped!" i.e. "Stop - not another word!"

One might have expected the aorist imperative (perfective 
imperative), but Democritus has in mind what led up to the 
imperative. The guy had been already said more then enough - 
the imperative is triggered by what has happened in the past 
and Democritus wants it to stop immediately once and for all.

Nid rhy hen neb i ddysgu.
There's none too old to learn.