“Our challenges may be new. The instruments with which we meet them may be new. But those values upon which our success depends — hard work and honesty, courage and fair play, tolerance and curiosity, loyalty and patriotism — these things are old. These things are true. They have been the quiet force of progress throughout our history. What is demanded then is a return to these truths. What is required of us now is a new era of responsibility — a recognition, on the part of every American, that we have duties to ourselves, our nation, and the world, duties that we do not grudgingly accept but rather seize gladly, firm in the knowledge that there is nothing so satisfying to the spirit, so defining of our character, than giving our all to a difficult task.”

2015, State of the Union Address (January 2015)

Life Without Principle (1863)

2014, Address to European Youth (March 2014)
Context: In the end, the success of our ideals comes down to us -- including the example of our own lives, our own societies. We know that there will always be intolerance. But instead of fearing the immigrant, we can welcome him. We can insist on policies that benefit the many, not just the few; that an age of globalization and dizzying change opens the door of opportunity to the marginalized, and not just a privileged few. Instead of targeting our gay and lesbian brothers and sisters, we can use our laws to protect their rights. Instead of defining ourselves in opposition to others, we can affirm the aspirations that we hold in common. That’s what will make America strong. That’s what will make Europe strong. That’s what makes us who we are. And just as we meet our responsibilities as individuals, we must be prepared to meet them as nations. Because we live in a world in which our ideals are going to be challenged again and again by forces that would drag us back into conflict or corruption. We can’t count on others to rise to meet those tests.

Independence Day speech (1828)

Remarks During Signing of Defense Bill http://www.washingtonpost.com/wp-dyn/articles/A42299-2004Aug5.html (5 August 2004).
2000s, 2004

Preface
Variant: Paraphrased variant: The difficulty lies not so much in developing new ideas as in escaping from old ones.
Source: The General Theory of Employment, Interest and Money (1936)

The Day the Universe Changed (1985), 10 - Worlds Without End

Quotes, IPI speech (2000)
Context: The disruption of the world's ecological systems — from the rise of global warming and the consequent damage to our climate balance, to the loss of living species and the depletion of ocean fisheries and forest habitats — continues at a frightening rate. Practically every day, it becomes clearer to us that must act now to protect our Earth, while preserving and creating jobs for our people.
And at the very same time that these threats are developing, the traditional nation-state itself is changing — as power moves upwards and downwards, to everything from supra-national organizations and coalitions all the way down to feuding clans. Susceptible to tyrants willing to exploit ethnic and religious rivalries, the weakest of these states have either imploded into civil war or threatened to lash out across their borders.
To meet these challenges requires cooperation on a scale not seen before. A realistic reading of the world today demands reinvigorated international and regional institutions. It demands that we confront threats before they spiral out of the control. And it requires American leadership — to protect our interests and uphold our values.

Part 3, Section 8
A Treatise of Human Nature (1739-40), Book 1: Of the understanding