I totally agree that psychology is a science as there is loads of observation it takes to make any sense of anything in any systematic form. As a UX Designer I have to use psychology all the time to create experience designs which work for people. If psychology wasn't a science, regular deployment of its rules would not be possible to create super successful products that work. I will be writing a post about how the whole stack of sciences actually works and builds up from first principles. It will somewhat compliment this article. Thank you for sharing this information.