"They are horses."
Translation:Is capaill iad.
You have a couple of things going on here. Let's take them one by one:
When the verb is an =, you have to use "is." Here you are saying "They=horses" You can't use Tá for =, only "is." (If you've learned Spanish, thinking of ser and estar may help.)
The normal word order in Irish is Verb Subject BlaBlaBla. When you use "is" to identify something/someone (like in this sentence), you switch things around: Is BlaBlaBla subject. Is fear é. Is úll é. Is t-leine (t-shirt) í. Is páistí iad.
And, to make things even MORE interesting, you have to use é/í/iad instead of sé/sí/siad.
All that from one little verb! Welcome to an Chopail, aka the copula.
Hope that helps a bit :)
If you want to tell WHAT they are, yes.
They are friends/horses/doctors. Is cairde/capaill/dochtúirí iad.
That's what I mean about an =. They equal friends/horses/doctors.
If you want to say WHERE or HOW they are, go ahead and use Tá siad ...
They are at home/here/blue/great. Tá siad sa bhaile/anseo/gorm/galánta.
They don't equal home/here/blue/great; those other words just tell us where they are or give a description.
I'm trying to explain it but my English is not good enough for that... I'm not sure if I'm right but I think the copula form is used here because the word horses is a noun. In sentences like "A is B" where A is the subject and B is a noun it requires this copula form. Maybe. I'm really not sure... Someone please tell me if I'm wrong :)
You're along the right track, but not quite! The phrase Tá siad capaill does not make sense in Irish. If you wanted to express your concept of "'they are horses right now or every so often but not all the time", you would have to say something like Tá siad ina gcapaill (literally "they are in their horses").
Another example of this construction that makes more sense: Is aisteoir mé, I am an actor; Tá mé i m'aisteoir, I am an actor [at the moment] (literally, "I am in my actor").