My daughter tried the same thing. She thought she should wear panties, but yet she refused to always use the toilet. First I wouldn't let her wear panties for a week. I told her that they are only for big girls that use the toilet. So she finally decided that she was going to be a big girl. Then I tried the potty training in a day thing my mom told me about. I would keep giving her drinks, juice, water, etc... Then every 15 minutes I had to bring her to the toilet. If she didn't go then I waited 5 minutes and took her again. The time will vary on each child. My mom told me every 30 minutes to an hour, but with my daughter if I didn't do it every 15-20 minutes she had an accident.
This is a lot of work for you as a parent, but it does work. Remember every time they go potty to give them another drink. We still have bad days where she will go in her pants. Mostly when she has friends over or is at someone elses houses. I've also learned that if they tell you they don't have to go, chances are they do but they just don't want to stop playing. Don't ask him if he has to go potty. What he will hear is do you want to go potty. And the answer will almost always be no. Instead say It's time to go potty. Make it fun for him. Reward him when he does go. Especially the first day. Then cut it down to every few times he goes. Then if he keeps his pants dry all day. Then if he keeps them dry for a week. Eventually you won't have to reward him for going and it will become habit for him. Hope this helps!