Hoigh, an dithis agaibh! or Personal numerals

Why does Gaelic have special numbers for counting people? It just does. Some languages do, some don't - some even have special counting words for men and women - so don't complain, there's only ten to be learnt in Gaelic. Here's the numbers first, the dreaded footnotes are at the bottom:

№	counting people (irregular nouns)	counting people (regular nouns)	plural nouns
1	aonar mór aonar mór	aonar mór aonar mór	aonar mór
2	dithis fhear móra dithis bhalach móra	dithis bhan móra dithis chloinne móire	dithis chaileagan móra
3	triùir fhear móra triùir bhalach móra	triùir bhan móra triùir chaileagan móra	triùir chloinne móire
4	ceathrar fhear móra ceathrar bhalach móra	ceathrar bhan móra ceathrar chaileagan móra	ceathrar cloinne móire
5	cóignear fhear móra cóignear bhalach móra	cóignear bhan móra cóignear chaileagan móra	cóignear cloinne móire
6	sianar fhear móra sianar bhalach móra	sianar bhan móra sianar chaileagan móra	sianar cloinne móire
7	seachdnar fhear móra seachdnar bhalach móra	seachdnar bhan móra seachdnar chaileagan móra	seachdnar cloinne móire
8	ochdnar fhear móra ochdnar bhalach móra	ochdnar bhan móra ochdnar chaileagan móra	ochdnar cloinne móire
9	naonar fhear móra naonar bhalach móra	naonar bhan móra naonar chaileagan móra	naonar cloinne móire
10	deichnear fhear móra deichnear bhalach móra	deichnear bhan móra deichnear chaileagan móra	deichnear cloinne móire

1. Because they are (grammatically speaking) nouns, the numbers for counting people are followed by the genitive plural. Just as with other nouns, the plural genitive gets lenited when indefinite. Thus we have dithis fhear or dithis ghillean (lit. two of men/boys) but na dithis fear and na dithis gillean 'the two men/boys'. If it helps, you can think of these numbers as a "twosome, threesome, foursome of children, men, girls, grannies ...", it explains the genitive anyway.
2. Again, as with many rules in any languages, you will hear people say things differently - many Gaels say cóignear nighean instead of nigheannan ...
3. So just remember to use these as nouns - things like chunnaic mi dithis or an do rinn na triùir agaibh an obair? are perfectly ok.
4. Also, you only use them up to ten, after that, you count people like things, that's why you won't see that column anymore further down.
5. Gender. Yes, gender. Seeing these are all nouns, they need a gender. They are all masculine, except for dithis and triùir, so if you follow these with an adjective, it gets lenited e.g. dithis mhóra, triùir bheaga but cóignear bochda.
6. As a result, remember to prefix t- before ochdnar, e.g. in thàinig an t-ochndnar aca fadalach 'the eight of them came late'.
7. Instead of naonar, you also hear naoinear and instead of dithis dithist.
8. Even though 2 takes the dual with the ordinal/cardinal numbers, dithis is followed by the plural. Fun, eh? Remind me to tell you about counting in the Chinese languages one day.
9. Plural nouns take the only genitive the have, so clann becomes cloinne and it lenites after dithis and triùir. We haven't been able to think of a masculine plural nouns denoting living beings - do let us know if you can think of one.

The last thing to remember is that because they are nouns, these can stand on their own, e.g. thàinig an dithis a-steach 'the two (of them) came in' or chaidh triùir a-mach 'three (of them) went out'.