Sentence (question) ending かい - how is it different from just か?

Question

I sometimes find questions that are normally ended with the question particle か to end with かい. For example: > いいかい？ > そうかい？ > あいつがどうかしたかい？ And sometimes with just い without か (if I understand this one right): > なんだい？ Is かい a softer version of か? How is it used?

Answer 1

KAI is basically an informal (masculine) way of asking a yes-no type question.