What key concept did Voltaire contribute that is reflected in the U.S. Constitution?

Voltaire's most significant contribution that is reflected in the U.S. Constitution is his advocacy for freedom of speech. He was a prominent Enlightenment thinker who championed individual rights and believed that a fundamental aspect of a functioning democracy is the protection of the freedom to express one's opinions, even when those opinions are contrary to the prevailing views of society or government. This belief is encapsulated in the First Amendment of the U.S. Constitution, which guarantees the right to free speech and expression.

In the context of his work, Voltaire often critiqued oppressive governments and religious intolerance, emphasizing the importance of open dialogue and the exchange of ideas as a vehicle for social progress. His famous quote, "I disapprove of what you say, but I will defend to the death your right to say it," illustrates his commitment to these principles. This foundational idea of free speech became a critical component of American political philosophy and is central to protecting the rights of individuals within the democratic framework established in the Constitution.