To bi or not to bi

So you're tearing your hair a bit over whether to pick tha or is for a sentence, why everyone keeps giving you rules that don't quite work and why oh why in the first place should you have to pick?

First off, "why" is a legitimate question if you're curious as to the history. We'll set that aside for now. Why-oh-why does Gaelic need two of these on the other hand is less legit as a question. It's a bit like telling a date you *LOVE* them but they really need to do something about their nose... Their nose is part of what makes them them and if you can't live with the nose, then perhaps your dating for the wrong reasons... So this tha/is (it's technically bi vs is by the way) is just part of what makes Gaelic special. Not the same as French and Spanish. Part of its charm. So learn to live with it or even better, love it.

To business

It's not actually a hugely difficult rule but there are a few grammatical concepts you need to master before the rule becomes simple and universal. I'll simplify slightly so please no definition nitpickers!

1. What's a subject? Well, in the grammatical sense, it's the main actor of a sentence, the thing or person carrying out the main action. It can be a name (e.g. Jamila), a noun (e.g. drongo), a pronoun (e.g. she): Jamila went to the shop. In the absence of the '32, Jamie decided to open a bottle of the '35. The flipping drongo learned how to mimic my alarm clock. She is a space pirate.

2. What's a predicate? Setting aside the main verb, the predicate is the bit of the sentence that tells you something about the subject. In English, which was Subject-Verb-Object word order, it usually is the bit that comes after the verb. It's what comes after you've answered the question of who or what did it? and did what?: Jamila went to the shop. In the absence of the '32, Jamie decided to open a bottle of the '35. The flipping drongo learned how to mimic my alarm clock. She is a space pirate.

Not hugely difficult, admit it!

Yeah but how does that help me?

Patience, I'm setting the scene for an epic showdown, [insert name] and the Two Verbs.

So when you have verbs like learned, decided or went, the question of whether you need bi or is doesn't arise because your main verb will be learn, decide, go and so on. The conundrum only arises when you run into am, are, is, was, were etc. Don't scoff, this narrows down the number of cases where you have to go hunt for the predicate.

The rule is this:

If the predicate of a sentence is a noun, pronoun or noun phrase, you need is ('s/bu/b'). In all other cases, you need a form of bi (tha, bha, bidh...)

The first two are really easy. Look for the subject and verb and then check if the next word. If it's a name or pronoun, case closed: I(S) was(V) Hamlet » Hamlet is a name, so we need is They(S) are(V) Jamie, Donalda and Mary » Jamie, Donalda and Mary are names, so we need is Frank(S) will be(V) me' » me is a pronoun, so we need is Jamila(S) is(V) her » her is a pronoun, so we need is

The next case, noun, isn't too hard either. The important thing to remember is to ignore articles (a, an, the), numbers (one, two...) and possessives (my, your, his...): I(S) was(V) a teacher » we ignore a, teacher is a noun, so we need is They(S) were(V) my teachers » we ignore my, teachers is a noun, so we need is Jamila(S) will be(V) two pirates » we ignore two, pirates is a noun, so we need is

The last case is a little more tricky because it can be quite long, a noun phrase. But essentially that's a phrase built around a noun. Here's a classic example: This(S) is(V) the house that Jack built. Technically that whole thing there is the predicate and technically, that makes it a noun phrase rather than just a plain noun. But you can see how it's all piled up on top of house so that makes it a noun at heart, so we need is.

So this excludes...

Well, most other things, for example adjectives: Donalda(S) is(V) amazing » amazing is not a name or pronoun, so we need bi

One important one that is potentially confusing is prepositional phrases. That's a bit of sentence that's built around a noun but starts with a preposition (on, at, through...). Those do not count as nouns or noun phrases, not the way Gaelic looks at it: Donald(S) is(V) on the truck » even though truck is a noun, the predicate starts with a preposition, so this does not count as a noun or noun phrase, so we need bi.

There's a few additional points I'll add at a later point, but in essence, this is it.

I've done you a summary as a flow chart (feel free to copy/save/share):