Opposite logic

In the car this morning, we were talking about opposites. James was very quiet until the end...

Me: What is the opposite of fast?
Philip: Slow!
Me: What is the opposite of hot?
Philip: Cold!
Me: What is the opposite of sad? Jamie, do you know?
Philip: Hot!
(several more opposites went this way, with Philip answering all of them)
Me: What is the opposite of hard?
James: NOT HARD!

Then James had one for me. I was stumped, but Philip came to my rescue:
James: What is the opposite of car?
Philip: Drive!

And they say boys are falling behind academically? Not on your life.