“M it is” is the same as “It is M”. That makes M a predicate nominative. (And yes, I’m sure.) “It is raining”, on the other hand, is a predicate gerund. One is a copula, and one is not.
I disagree, because normally if you say “It is M”, you have some clear referent for the pronoun. “What’s your first initial?” “It is M.”
But when you say “M it is”, there’s no clear referent for the pronoun. The “it” functions similarly to the “it” in the formation “It is raining”. It’s an expletive, a mere placeholder for the syntax. What you’re essentially saying is “rain is falling”. Similarly, with “M it is” you’re essentially saying “I choose M”.
So I’m not sure that you can call “M” a predicate nominative in that stucture.
But I am.
When you say “M it is”, you are using the third person singular present of “to be” as a copula — that is, as an identity. You could render the expression mathematically as M = it, or logically as a biconditional implication: M <-> It. Since equality is commutative in math, we can also say It = M. And since biconditional implications imply one another in logic, we can also say It <-> M That’s how a copula functions.
In the expression, “It is raining”, however, “raining” is not the only thing “it” is — that is, raining does not identify “it”. It could also be windy, for example. Or flooding. Or raining lightly like a mist, or stingingly sideways as in a hurricane. (Some languages migh differentiate such types of rain.) Or it could be NOT raining in many locations, some near you.
A copula always ties a nominative to a predicate nominative. A gerund or adjective phrase does not. For example, another sentence that is not a copula is, “He is harry.” (He is also other things.) But “He is Harry” — that IS a copula. It identifies him.
One downside, if you read the fine print, is that you have to help other paid members 24/7 no matter what. I have been called to change flat tires in the middle of the night, babysit, and I even have three of the bastards squatting at my place right now and I have no idea how to get rid of them because I signed this “contract”. Taking care of the goat on your rotation isn’t so bad because he is funny and keeps the weeds trimmed but he does tend to destroy stuff in your house.
Bastard ate my coffee cup. We now have a freezer full of goat meat.
No, you don’t always tie a nominative to a predicate nominative in that case. (And by the way, “raining” is a participle here, not a gerund.)
And mathematics and formal logic have nothing to do with it, since the brain does not process language according to those frameworks. Which makes most of your post irrelevant.
When we say “M it is”, we are not saying the same kind of thing as when we say “Heroes they were”, where “they” is certainly a pronoun with the same referent as “heroes”. Rather, we are saying something more akin to “M then” or “All right, M”.
In this case, the syntactic structure is merely a placeholder. Just as with the expression “It is raining”, the “it” has no referent. It’s empty syntax. We say it that way because our brains like it that way.
So yes, “M” is not an object here. That much I agree with. But psychologically, it functions as a subject. I can’t read it as a predicate nominative.
I’ll help anybody out, that’s no problem.
Goat destroys anything and I’m serving my guests cabrito.
I’ve checked “show avatars” on the CP, but I don’t see any. Does that require membership?
Which is essentially what I said you should have said or meant to say. I believe it was, “I choose ‘M’.”
Well, I must say, as a Southern Gentleman, that you have balls bigger than Magnolia blossoms. I mean, going all dingy on whether mathematics or logic apply to language, and then resolving your point by an appeal to psychology comes across to me a bit like the woman who won’t wear a properly fitted dress because it makes her look fat, and so just grabs the muumuu because she can’t cope with her body’s aging process. I’m not saying you’re fat, mind you. Nor am I suggesting that you wear a muumuu. They’re just what we in the South call metaphors. I’m enjoying our discussion, and I’d be interested in what they’re called where you come from.
That requires an act of God, unfortunately. The admins just get the vapors when they contemplate those extra 2K of bandwith usage. In plainer terms, there are no avatars. Nor are there likley to be, I’m afraid.
Well, we are of a type, I reckon.
Now let me say that an appeal to psychology is not inconsistent with a rejection of appeals to mathematics and formal logic when it comes to language, because there is a particular psychology to language and it is not the psychology of either of the others.
As for where I’m from, let’s just say that you can’t get much Southerner. However, I do not claim to be a gentleman. I’m a mutt, and I admit it.
And what you call “metaphors” we don’t give any name to at all. We just say, well that’s between him and Jesus.
You’ll fit in well, here, FatKid. I encourage you to join. 
Well, the shine has definitely gone off this forum for me.
It seems to be a community obsessed with petty grudges among old-timers.
Shame.
Don’t you know never to join any board that would have you as a member?
Avatars? We don’t need no steenkin’ avatars!
(I don’t think that feature has been enabled.)
[Bevis or Butthead]Henh, henh…he said “member”…Henh[/B or B]
Just goes to show you the level of discourse you are likely to find here, so don’t say you weren’t warned.
Isn’t this a passable description of just about every message board on the web? Except for those created yesterday, perhaps.
Thank you for filling out the comment card.
Since this thread is a little long in the tooth and has apparently both a beginning and an ending, let’s close.
Hope you find a board that’s more to your liking, FatKid.