What makes you think so?
なぜそう考えるの?
What makes you think so?
What is it that makes you think that way?
How did you come up with that idea?
What makes you think so?
なぜそう思うか
What makes you think so?
What makes you think so?
What makes you think so?
What is it that makes you think that way?
What do you really think about that?
How does that strike you?
どう思うか
I need your thoughts on this.
I'm wondering what you think about that.