What is an commonplace assertions in Douglass speech?

In Frederick Douglass's famous speech "What to the Slave Is the Fourth of July?", a commonplace assertion is the idea that freedom and justice are universally valued ideals. Douglass emphasizes the hypocrisy of celebrating liberty in a nation that practices slavery, highlighting the stark contrast between the principles of the Declaration of Independence and the reality faced by enslaved people. This assertion serves to challenge the audience's complacency regarding the nation's values and calls for a deeper reflection on true equality and justice.