WASHINGTON — Barack Hussein Obama ceremonially opened his second term on Monday with an assertive Inaugural Address that offered a robust articulation of modern liberalism in America, arguing that “preserving our individual freedoms ultimately requires collective action.”

On a day that echoed with refrains from the civil rights era and tributes to the Rev. Dr. Martin Luther King Jr., Mr. Obama dispensed with the post-partisan appeals of four years ago to lay out a forceful vision of advancing gay rights, showing more tolerance toward illegal immigrants, preserving the social welfare safety net and acting to stop climate change.

At times he used his speech, delivered from the West Front of the Capitol, to reprise arguments from the fall campaign, rebutting the notion expressed by conservative opponents that America risks becoming “a nation of takers” and extolling the value of proactive government in society. Instead of declaring the end of “petty grievances,” as he did taking the oath as the 44th president in 2009, he challenged Republicans to step back from their staunch opposition to his agenda.

“Progress does not compel us to settle centuries-old debates about the role of government for all time — but it does require us to act in our time,” he said in the 18-minute address. “For now decisions are upon us, and we cannot afford delay. We cannot mistake absolutism for principle or substitute spectacle for politics or treat name-calling as reasoned debate. We must act.”