The Three Bs

Every language has it's how do you spell that again? words. Even languages which don't bother with letters - in Cantonese for instance, there's a three way confusion over 己 (géi 'self'), 已 (yíh 'already') and 巳 (jih ... something related to the Chinese zodiac). And it all hinges on whether you start that swervy 乚 at the very top of the 'box', the middle or the bottom. Bah humbug...

Not to be outdone, Gaelic has such things too of course. Like the Three Bs - bidh, bi and bith - all pronouced [bi] though bidh when emphasized can be long [biː].

So how do you know which one to use? Fortunately, they all appear in different environments i.e. you can tell which spelling is needed if you consider where in the sentence it sits and what comes in front of it.

bith

This is very restricted in its use and appears, by and large in two scenarios:

• after the infinitive particle a. This causes lenition, resulting in a bhith and by and large, that only appears if there's a verbal noun following, for example a bhith ag ithe, a bhith ag èisteachd, a bhith a’ bualadh and so on.
• fixed particles/phrases and some phrasal verbs, where is functions as a normal verbal noun: a’ dol à bith 'going out of existence', sam bith 'that is in existence', bith-buan 'permanent existence'

bidh

This is also quite restricted. It's the so-called 'independent future' of the verb 'to be' and if you recall, independent in the context of Gaelic verbs by and large just means 'nothing sits in front'. So bidh is the one to go for if none of our an/chan/nach... particles sit in front: bidh seo math, bidh iad fuar, bidh mi a’ dol ann

Note that this may appear at the start of a subclause i.e. a sentence that sits within a sentence, but there's usually a very noticeable logical break, often with a comma or a conjunction like agus, ach...: ma thèid thu a Nis, bidh e fuar sa gheamhradh

This is the one which - when used very emphatically - can be written as bithidh

bi

This one is perhaps the most common one and appears in two distinct scenarios.

• as the 'dependent future' of the verb 'to be' which means that a grammatical particle has to come right before it - an, chan, nach.... For example: am bi thu fuar? cha bhi thu fuar nach bi thu fuar?
• the root/dictionary form and since that in Gaelic is the imperative i.e. when ordering around someone around, that's the scenario that you will find this in, by and large. Note that the imperative bi may be preceded by the particle na: bi sàmhach!, na bi gòrach!

That's it, off the top of my head - but if I've forgotten a scenario, let me know!