I am a teacher

OK, as far as I know, there are three ways to say this in Irish


1. Is múinteoir atá ionam
2. Tá mé i mo mhúinteoir
3. Is múinteoir me

Correct me if I'm wrong, but the differences in meaning are as follows.

1. Being a teacher is my vocation and calling in life
2. I'm a teacher for now out of necessity, but it's not what I really want to be doing
3. Sort of neutral statement halfway between the other two

Am I right, or am I way off base here??

The first should be "múinteoir atá ionam". I think technically you can say "Is é múinteoir atá ionam" but the "is é" is highly superfluous. The other two are correct.

Here is my take on how you're interpreting them: I could be wrong, but I think you're way off base. They are all pretty much identical in meaning. You are inferring far too much meaning from simple statements of fact about having a job.

Not far way off

2)
(usually without "is")
I am a teacher, i.e. I fulfill all requirements to be called a teacher.
It may have a meaning of attainment (yesterday I was a student, but today I'm already a teacher) or temporality (I work as a teacher now but I want to become an author)

3)
I am a teacher - period (as Sean Spicer would say)

1)
This is just an emphasized version of 2) (and of 3)) It is a teacher that I am.

No, that doesn't work.
But you could say: "Is é atá ionam (ná) múinteoir" - "What I am is a teacher."

GRMA

Usually the construction with "tá" is used to indicate either a temporary state or a recently attained state.

Redwolf

And let's not forget "Múinteoir is ea mé".

not always. You can say "Is é Micheál Ruadh atá ann" = he is red-hairead Micheál. It's not temporary.
Or "Préachán atá ann." it's a raven. Not temporary. The "atá ann" pattern is just an alternative pattern to the "is" one, especially in Donegal.

_________________
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Agus is í Gaeilg Ġaoṫ Doḃair is binne

Methinks Redwolf was referring to yon "tá mé i mo..." thing.

Yes, exactly. I'm well-familiar with Is ____ atá ann.

Redwolf