Radicalism was a political movement representing the leftward flank of liberalism during the late 18th and early 19th centuries and a precursor to social liberalism, social democracy, civil libertarianism, and modern progressivism. This ideology is commonly referred to as "radicalism" but is sometimes referred to as radical liberalism, or classical radicalism, to distinguish it from radical politics. Its earliest beginnings are to be found during the English Civil War with the Levellers and later the Radical Whigs.

Progressivism is a political philosophy and movement that seeks to advance the human condition through social reform – primarily based on purported advancements in social organization, science, and technology. Adherents hold that progressivism has universal application and endeavor to spread this idea to human societies everywhere. Progressivism arose during the Age of Enlightenment out of the belief that civility in Europe was improving due to the application of new empirical knowledge.