According to media reports, Vice President Joe Biden advised graduates of the University of Pennsylvania School of Social Policy and Practice to stay optimistic and "make things better."

Change is under way in the United States and urged graduates to stay positive despite an array of problems that includes a deep recession and two wars, Biden, whose daughter Ashley Biden was among the 150 students graduating Monday from the school of social work and social policy, told the commencement audience.

Biden said, "The thing that I love about you all … is that you believe in possibilities, the possibility that you can make things better."

The vice president told the graduates belief that one can make things better is what makes progress possible.

He said, "If the day comes when you lose that sense of possibility, if you lose that optimism please do me and yourself a favor … leave. Leave the profession."

Biden told the graduates change comes "one policy, one person at a time" and warned them to be vigilant against abuse of power by government officials.

He further said, "For social justice to reign there must be a mechanism -- to restrain the abuse of power." (With Inputs from Agencies)