Wordpress Theme - Adding jQuery

I recently had a WordPress theme custom made for me and I had a falling out with one of the designers so I decided to not have them code it.
I found another coder who does freelance work but I want him to add jQuery to the Wordpress theme. He told me it is not possible.

Is he right? I am not too sure with these CMS’s now a days if they are capable or not.

Hi there,

This is most definitely not correct.
jQuery is a default script included and registered by WP.

mostly of my projects creating wp theme I used jquery, in content slides, video background etc.