De ⁊ A
You'll probably have come across a - this somewhat odd looking preposition already. It occurs quite a lot in the written language and perhaps even more often in the spoken language. You may also have come across authors of grammar books lamenting its existence going back as far as the year dot.
The reason they're lamenting comes down to the fact that in colloquial speech Gaelic has merged two prepositions - de and do into a. But there's little point in closing your eyes to reality - this funny a is here to stay, so we have to learn how to deal with it. Here are a few examples to begin with:
|chaidh e a dh'Éirinn||he went to Ireland|
|thig a Chanada||come to Canada|
|thug e duais dh'athair||he gave a prize to his father|
|gu leòr a dh'ùbhlan||enough (of) apples|
|a bheag a dh'ùbhlan||a few (of) apples|
|càil a dh'fhios||any (of) knowledge|
|dad a thìde||any (of) time|
|a latha 's a dh'oidhche||by day and night|
First, let's look at how on earth you get from do and de to a schwa. Actually, it's quite easy if you remember first, that function particles lead a precarious life, and second, that lenition is rife in the Celtic languages.
|do [dɔ]||⇨||dha [ɣa]||⇨||dha [ɣə]||⇨||a [ə]|
|de [dʲe]||⇨||dhe [ʝe]||⇨||a [ə]|
Anyway, things went more or less like. It's not 100% clear cut because, as you can see in the third example above, do + a gets merged into dh'. Here, the legitimate question to ask is how a language can merge two words which mean opposite things. The reason is context.
Languages rely heavily on context and what is known as "knowledge of the world" to encode meaning. Take one of Groucho Marx' famous quotes: "I once shot an elephant in my pyjamas". This sentence is funny because it can have two meanings - either that you were wearing your pyjamas or that the elephant was in your pyjamas. Because you're watching a Marx Brothers movie, you expect a joke so it's potentially ambiguous. But, if you were telling this story to a friend who knows you do a lot of game hunting in Africa, he will infer that you were wearing your own pyjamas when you shot the poor pachyderm. Or take the sentence "Frank believed that he would succeed". Who will succeed, Frank or some other chap? You can't really tell, but then again, language is seldom completely without context.
Which is exactly what is happening here. Take the first example - chaidh e a dh'Éirinn. There is only one logical solution as to what the intended meaning is, namely that the intended meaning is "to". Simply because you could not make a sentence like *chaidh e de dh'Éirinn without getting funny looks in the pub. Take another one - cha robh dad a thìde agam. It can only be an underlying de, otherwise it just does not make sense. Context is the reason why spoken Gaelic can afford to merge these two words.
So, it's perfectly OK to use this a, especially in spoken Gaelic and even in written Gaelic. If the outcome is ambiguous and you want to be 100% certain you are not misunderstood, you can use de or do as appropriate.
|᚛ á - aig - air - ann an - de ⁊ a - do ⁊ a - eadar - fo - gu - le - mu - o ⁊ bho - os ⁊ fos - ri - tro - thar ᚜|