The idea that people could govern themselves, that they didn't need the rule, benevolent or otherwise, of a monarch or of a small clique, was - in a word - revolutionary. And we fought our Revolution over it.
Yet since America became an independent nation of free individuals, there have been those who have given up a measure of their freedom so that the rest of us could have ours.
Many have given up the most fundamental of the divinely ordained rights enumerated in the Declaration of Independence: their lives.
Memorial Day honors them, those who served their country in the military and paid the ultimate price.
No one in our history has summarized their sacrifice - and the obligations of the rest of us - any better than Abraham Lincoln in his Gettysburg Address. The nation was still young and was undergoing a severe test. Of those who died in battle, Lincoln said:
"The world will little note, nor long remember, what we say here, but it can never forget what they did here. It is rather for us, the living, to be dedicated here to the unfinished work, which they who have fought here have thus far so nobly advanced.
"It is rather for us to be dedicated to the great task remaining before us - that from these honored dead we take increased devotion to that cause for which they gave their last full measure of devotion - that we here highly resolve that these dead shall not have died in vain - that this nation, under God, shall have a new birth of freedom - and that government of the people, by the people and for the people shall not perish from the earth."
How often do we consider, as Lincoln did, that the best way to honor those who have given their lives in service to this country is to ensure that the ideal of liberty and self-governance survives?
That requires work from all of us, not just those in this era of an all-volunteer military force whose job it is to protect us.
That system of self-governance gets less participation and more cynicism with each passing year. Some believe it is at risk of falling to indifference and complacency.
How can we possibly give up on - or drop out of - a system of government that so many have died to preserve? We can't, if we are to honor them at all.