Let's sidestep for the moment the overstretched meaning of 'de' in Esperanto, and compare.

1. Jam multajn jarojn mi ne vidis lin.
2. Eke multajn jarojn mi ne vidis lin.

The first seems to correspond very closely in meaning to Jam de multaj jaroj .. and Jam dum multaj jaroj ...

But the second does not easily translate into Eke dum multaj jaroj .. .

The first can be rewritten (albeit inelegantly) as Mi jam ne vidis lin dum multaj jaroj.

The second rewritten as Mi eke vidis lin dum multaj jaroj stretches the meaning beyond breaking point. It is not just inelegant, but almost incomprehensible.

Now what is the meaning of 'de'?

In a broad sense it is the origin of something, and it does not carry with it the idea of any extension in that origin. Sometimes 'de' serves just to characterize (ŝtofo de ruĝa koloro).

In De Parizo al Berlino, whilst Parizo has extension it is not relevant.

Mi venis de multaj mejloj jars. More comfortable is Mi venis de multaj mejloj for de ĉi tie which serves to locate.

Agreed that de multaj jaroj is established in the sense of a characterizing length of time.

So we can say amiko de multaj jaroj and even mi parolas Esperanton de multaj jaroj.

However, once you stick EK into the mix, with its meaning of beginning (or short duration), this builds a certain tension between the elastic extension of 'de' - beyond its point of origin sense to periods - and the meaning of EK.

Sudanglo, I didn't respond immediately to your last two posts as I wanted to take a little break, so that I could then try to look at the situation with a fresh mind.

To be honest, I remember that when I first saw an expression such as 'ekde du jaroj', it also made me wonder whether it is a correct form or not. I took a look in PMEG and found the example sentence "Nur de ses monatoj mi scias la veron." I immediately interpreted that as justification also for 'ekde', as I find it very difficult to see what the problem is with that. To my mind, if one accepts 'DE du jaroj', then one should equally accept 'EKDE du jaroj' - the basic concept behind these two expressions is the same.

In a sentence such as 'de du jaroj', what is the function of 'de'? According to PMEG, it "shows the beginning moment of a continuing action or state" Note the word 'beginning moment', something which 'ek-' also tends to mark.

PMEG describes 'ek-' as marking the 'beginning of an action, a sudden action' (= komenco de ago, subita ago). It's important to note that ek- does not always mean a sudden, short-lived action. It can also mark the beginning of a longer action (for example: Mi eklernis Esperanton en 2005, kaj mi ankoraŭ lernas ĝin nun!) This is why PMEG divides the examples of 'ek' into two parts: Komenciĝo (=beginning) and Subiteco (=suddenness).

sudanglo:Let's sidestep for the moment the overstretched meaning of 'de' in Esperanto, and compare.

1. Jam multajn jarojn mi ne vidis lin.
2. Eke multajn jarojn mi ne vidis lin.

The first seems to correspond very closely in meaning to Jam de multaj jaroj .. and Jam dum multaj jaroj ...

But the second does not easily translate into Eke dum multaj jaroj .. .

The first can be rewritten (albeit inelegantly) as Mi jam ne vidis lin dum multaj jaroj.

The second rewritten as Mi eke vidis lin dum multaj jaroj stretches the meaning beyond breaking point. It is not just inelegant, but almost incomprehensible.

I'm still trying to work out the examples that you give. I feel there's something not quite right with the comparison you're making there, but I can't quite put my finger on it at the moment.

sudanglo:However, once you stick EK into the mix, with its meaning of beginning (or short duration), this builds a certain tension between the elastic extension of 'de' - beyond its point of origin sense to periods - and the meaning of EK.

Yes, 'ek-' indicates the beginning of something. This aspect of ek- doesn't seem out of place in an expression such as 'ekde du jaroj', which precisely means 'since the beginning of a period of two years' - just like 'jam de du jaroj'.

PMEG says that if 'de' is placed before an expression of a time period, then it shows that the two durations (daŭroj) start at more or less the same time:

Nur de ses monatoj mi scias la veron. = Nur antaŭ ses monatoj mi EKsciis la veron. = From the beginning of a period of only six months I have known the truth. (As with 'jam de', there is an implied 'antaŭ', as Tommjames put it.)

To my mind, if one accepts 'DE du jaroj', then one should equally accept 'EKDE du jaroj' - the basic concept behind these two expressions is the same.

This goes to the heart of the matter.

I argue that de multaj jaroj characterizes, which is the function of 'de' in amiko de multaj jaroj or in ŝtofo de pura blanko.

If you interpret the 'de' in de multaj jaroj mi scias la veron as meaning from or originating, it comes to the same thing as seeing it as charactizing your knowing.

With amiko de multaj jaroj you get a diversion of meaning depending on your analysis. A friend from years ago or a long-time friend. Now I think the meaning of amiko de multaj jaroj is the latter.

I talk of amiko de miaj lernejaj jaroj. That doesn't mean that he continued to be my friend after we both left school. Amiko ekde miaj lernejaj jaroj does imply that.

Therefore 'de' doesn't equate to ekde. And ekde requires a point in time - the analysis of La Akademio.

sudanglo:I argue that de multaj jaroj characterizes, which is the function of 'de' in amiko de multaj jaroj or in ŝtofo de pura blanko.

If you interpret the 'de' in de multaj jaroj mi scias la veron as meaning from or originating, it comes to the same thing as seeing it as charactizing your knowing.

An interesting idea. I'll have to think about it...

sudanglo:
...the analysis of La Akademio.

Yes, regarding the analysis of La Akademio, nobody has yet explained the meaning of the following:

Bonvolu noti, ke en la frazoj, kiujn vi citis, oni povas interpreti
“ekde N jaroj” ankaŭ kiel indikon de komenca tempopunkto kun
la signifo “ekde la tempopunkto kiu okazis antaŭ N jaroj”. Do,
tiuj frazoj estas misinterpreteblaj, sed ne nepre misinterpretendaj

- the above quote still doesn't make any sense to me. Sudanglo, perhaps you could help me out?

So, using the above words of la Akademio:

Mi lernas Esperanton ekde du jaroj = Mi lernas Esperanton ekde tempopunkto, kiu okazis antaŭ du jaroj.

Er, am I missing something? What's the problem with that? Isn't that exactly the same meaning as 'Mi lernas Esperanton DE du jaroj'?

Presumably, if you place 'jam' before 'de', then that has the additional nuance of adding the notion of 'already'... So, if you use 'jam de du jaroj', then perhaps the time has flown by...

Ok, I now know what the representative from the Academy meant by that quote which has been bothering me. He was referring to the sentence: "Ekde tri jaroj la pesto furiozIs en la lando”

- The important factor is the usage of the past tense 'furiozis'. In this context, it's perfectly clear what the akademiano was getting at. Obviously, if you say 'De tri jaroj la pesto furiozis en la lando', the 'de' is not absolutely in relation to the present (it could be referring to a three-year time period starting in, say, 1567). Whereas, 'ekde' in cases such as 'ekde 2002' etc, is set rigidly in relation to the present. So, perhaps someone could understand such a sentence as meaning that the plague ravaged the land from 2009 to the present.

This might well be a pretty good point regarding verbs in the past tense. However, when you focus on sentences with the verb in the present tense, such a problem is not at all evident.

EDIT: A little doubt - could someone really misunderstand such a sentence with 'ekde'? After all, if it refers to something that started three years ago and continues in the present, then you'd use the present tense anyway! If it was a finished event, then I doubt that you'd use '(jam) de tri jaroj' in such a sentence. Isn't this concept of '(jam) de' reserved for on-going events?

EDIT no.2: I think the above post represents what the Academy was getting at by a 'possible misunderstanding', but I'm now not really sure how such a misunderstanding could in fact arise, as mentioned in my following posts!

Chainy:Mi lernas Esperanton ekde du jaroj = Mi lernas Esperanton ekde tempopunkto, kiu okazis antaŭ du jaroj.

Er, am I missing something? What's the problem with that?

I don't think there's anything wrong with it, but I would agree that there is a certain "semantic tension" there, as sudanglo puts it. Du jaroj has to be read as la komenca tempopunkto de du jaroj, or antaŭ du jaroj.

I don't consider that problematic, and the expression is established in the language anyway so I'm not particularly inclined to rail against it. Nevertheless I do think it's a turn of phrase that can be a cause of doubt in some cases (you admitted that you yourself felt this when you first heard the expression). So in my view it would generally be better to do what Shlafer proposes and use "antaŭ", regardless of any perceived chance of misunderstanding with regards to continuation of the action into the present.