Always use o in speaking of members of the body, clothes, houses, names, medicine, water for drinking, washing &c., but a in speaking of work, food &c.
Examples.
Tona kakahu, his garment.
Ou waewae, your feet.
He kai mau, food for you.
Tetahi wai moku, some water for me.
Tou ingoa, your name.
Taku ingoa mou, my name for you (i. e. which I have given you).
Obs. To, thy, plural o, resembles tau rather than tou in the way in which it is used, though it often appears to be used indiscriminately for either.