linguoboy wrote:It could be san, but not sa in this case because uisce starts with a vowel.
Oh, right. I forgot about the added n before vowels. Thanks for reminding me.
(I'm not sure if they were being deliberately archaic by including insan in some of the examples or if it was still found among older dialect speakers at the time TYI was published.)
Perhaps it's like their usage of the dative plural ending in some exercises then? They do seem keen to teach some archaisms in TYI.