President Barack Obama says "we must act" even if our work is imperfect. He says we cannot afford to delay.

In a message that could be aimed at the divided Congress where battles await him in his second term, Obama is cautioning against mistaking absolutism for principle, substituting spectacle for politics or treating "name-calling as reasoned debate."

Even so, Obama says that today's accomplishments will be partial, and it will be up to people four, 40 or even 400 years from now to advance them further.

The president spoke at the U.S. Capitol after taking his public oath of office for his second term.