As you can see, a Sheáin, before we even get to the specific question here, there are two conflicting views about the copula, the "permanent vs transitive" model and the "nouns vs everything else", both of which have elements of truth and neither of which is perfect in and of itself.
The only sure thing I know about the copula is that if you express either one of these views on its own, the other camp will be sure to shoot you down as a heathen or a traitor. (Welcome to Irish.

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The "permanent vs transitive" model runs into problems given that nothing is really ever permanent - even
Is fear é is not guaranteed to be permanent in this day and age.

(The "permanent" in this model is really only "semi-permanent", expressing "_what_ something is" (
at a given point in time). The transitive element expresses "_how_ or _where_ something is".)
The "nouns vs everything else" model also encounters problems because the copula gets used with adjectives for emphasis (no doubt from its "permanent" feel

), i.e.,
Is maith (é) sin "That's good!", and in "fronting" where any element of the sentence, be it a noun, an adverb, or an adjective, can be brought to the front of the sentence for emphasis, i.e.,
Is sa chistin atá sé "He's in the _kitchen_" literally "It is in the kitchen that he is."
It's a chicken-and-egg type problem given that nouns tend to be used for permanent descriptions and adjectives and adverbs for transient states anyway - but whichever way you try to explain it you'll run into problems.
Being a relativist, I am happy to believe in both at the same time, and use whichever suits me for the purposes at hand, just as I can safely assume that the world is "flat" when it suits me, such as when I am building something around my house and don't have to allow for the curvature of the earth (or the curvature of the space-time continuum for that matter.)

Or to use another analogy, does the sun revolve around the earth or vice versa? Answer: both - they both revolve around each other and perturb each other's orbits in proportion to their mass as do all bodies with mass in the solar system.
The fact is that both of these explanations work only in a very general way and neither is a panacea, in the end you just have to learn lots of examples.
That's where An Lon Dubh's explanation may come in very handy.
@An Lon Dubh - I'd suggest placing your entire explanation in
Nótaí an Loin Dhuibh and having a discussion thread in the main forum to look at it in more detail if we need to. (What's the bet we don't end up having this exact same argument all over again in the discussion thread?

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