Comparing tags

 so + auxiliaire + sujet = aussi

but + sujet + auxiliaire = contraire

neither + auxiliaire + sujet = non plus

affirmative  : so did I.   /  but I didn't.

negative :   neither did I  /  but I did

affirmative  : so did John.   /  but Robert didn't.

negative :   neither did Jane  /  but Judy did

Examples

Kevin went to Spain so did I.

I ate crabs but Robert didn't.

Harry didn't play golf neither did George.

I didn't buy postcards but Jack did.

The possessive tags.

Ronald's holidays were sunny, so were mine.

My holiday was great, so was his.

Our holidays were in Corsica, but John's weren't, neither were Mark's.

Remember - Possessive pronouns

mine

yours

his / hers

ours

theirs