Plurals shmurals and how to predict them

Ok, this is definitely work in progress but someone asked for this so I'll have a go.

First off, to quote Captain Barbosa, these are more like guidelines, plurals in most languages are hard to predict with certainty but there are some things that can make like easier.

Best bets

Your best bets are special endings (in the singular) which take fixed plurals.

-air/-(e)adair/-(a)iche/-(e)ar

These are agentive endings. Bits that you stick onto another noun to show that someone makes or does something, like -er in English which gives you fish » fisher, wash » washer, clean » cleaner and so on. The plural of these is almost invariably -(e)an:

• iasg » iasgair » iasgairean
• clach » clachair » clachairean
• saighdear » saighdearan
• cluich » cluicheadair » cluicheadairean
• mara » maraiche » maraichean

Careful, this only works if the noun is made up of a noun plus an ending. There are some feminine nouns which aren't "composed" like that which behave differently. As a rule of thumb, if you take the ending away and what you're left with doesn't make sense, then it's not one of these. For example, cathair and nathair, if you take the -air away, leave you with cath and nath and that just doesn't make sense, i.e. nath doesn't mean anything on it's own so it's not nath+air but just one word like that.