Learn English – So, Can linking verbs be used with “continuous tenses”

The English word commentator comes directly from Medieval Latin commentator. However, this Latin ancestor is labelled as rare and some dictionaries don't have it.

Classical Latin does not use commentator but instead prefers commentor.

Both are formed after the verb commentārī, but one can see that by adding the standard Latin agent noun suffix ("-or") to the verb yields "commentor".

Please note that the Latin verb commentārī had a much broader meaning. It can be used as any of the followings: "to consider thoroughly [thoughts]", "to prepare [exposé]"; "to invent", "to compose", "to write [literary works]".

For instance, "commentarius" has the meaning of "memorandum , notebook". Remember for instance the original Latin title "Commentarii de Bello Gallico" of Julius Caesar's ("Commentaries on the Gallic War"): these are actually not comments but a notebook, a relation (a title designed to be neutral but with an agenda as is well known).

I'm not too sure why Medieval Latin "commentator" came to supplement Classical Latin "commentor" but I speculate that this is related to the gradual loss of meaning as "to invent" and to the consequent specialisation as "to expound" in which case "commentator" would be formed after "commentarius" the noun (this Julian "Commentarii" really looked like comments).

So we have "commentary" and "comment" (just as we have documentary and document).

Looking up both words in the Century Dictionary shows the nuance:

• A commentator "makes comments or critical or expository notes upon a book or other writing".
• A commenter "makes remarks about actions, opinions, etc.".

There's a whiff of scholarship in the commentator that is absent from the mere commenter.

I don't deny that musicality or morphological consistency have a role to play in our vocabulary. However, and this is particularly true of English, I would argue that when several words with close signification are in competition, they tend to specialise and contribute to the language's richness.

In that particular case the reason why we might be more attracted to the variant "commentator" is possibly because of its perceived higher quality standard.

Nevertheless, the word "commenter", having a long history of its own also has its dedicated niche where it is preferably used.

A significant proportion of the COCA corpus entries I found had "commenter" associated with "anonymous" or "typical": sounds better than "anonymous commentator" this time.

The observation behind this question is very nice. Use of this locution in indeed limited, to perfect tenses:

1. Present perfect: I have been to London to visit the Queen
2. Past perfect (pluperfect): I had never been to London before you took me
3. Future perfect: I will have been to London by the time you return

You can clearly imagine putting the phrase into other tenses. For instance, by analogy of I have been silly to I am (being) silly, you could form *I am to London, *I am being to London. Similarly, you expect *I was to London (I was silly) and *I will be to London (I will be silly). But none of these are possible.

Note 1. It is wrong to think of to have been as having have as a main verb. If so, one would expect the possibility of the past perfect have had been (comparing to, say, have had it coming), and this is clearly impossible.

Note 2. There is a (rather outmoded English?) idiom to have been, without any destination/location specified. It is a euphemism for going to the toilet. Monty Python made a recurrent joke out of it in a skit based around an Agatha-Christie-style murder (the reluctance to say murdered led to numerous characters asking simply Has he been ... ?, to which the others would answer something like Yes, before lunch).