Modern Greek perfect:
>The auxiliary always agrees with the subject, and the pronoun is
>only employed for emphasis. Other than that, it is all very similar
>to French, German, English etc. and fits with what you have been
>saying.
This is not entirely true, since in the German/Romance perfect the
participle has at least partly an adjectival function - hence its agreement.
But the Greek equivalent cannot be called a participle, and does not change.
It has grown out of an older aorist infinitive, which now survives nowhere
else.
A lesser difference is that the German/Romance perfect can function as a
simple past tense (e.g in spoken French, Northern Italian or Southern
German), whereas the Greek perfect is at least theoretically always
distinguished in meaning from a simple past - it refers to a completed
action whose consequences are being described in the present. There are
many instances where simple past and perfect appear interchangeable in
Greek, but many others where they are not. This is not the situation in
Southern German or spoken French, where the perfect has replaced the simple
past.
Peter