From Roman freedom to Viking happiness, the iconic words in the Declaration of Independence reveal thousands of years of humans wrestling with how to live well together – and the power of language to put those ideas into action. "We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness." When Thomas Jefferson drafted these words in the Declaration of Independence, two things were on his mind. One: he needed to find "terms so plain and...