The best synonym for external validity is

our founding fathers introduced the revolutionary idea that each person's desire to pursue their idea of happiness was not self-indulgence, but a necessary driver of a prosperous society. they created a government to defend that right for everyone.

i highly recommend james madison. the work is simple and if you stick to it you can graduate quickly. the work is simple and the teachers are very interactive. the flow of the school work is all on your time so it's not really a dead line. go on their website and look at pricing and enrollment plans. i know when i signed up i got a discount. you pay a certain amount of money every month. it's kind of expensive but i did it in 6 days tops with just my senior year left : )