If you take a dim view of our political parties, you’re in sterling company. So did George Washington.

In his famous farewell address, he warned us against “the baneful effects of the spirit of [political] party.” A political party, he wrote, “agitates the community with ill-founded jealousies and false alarms, kindles the animosity of one part against another, foments occasionally riot and insurrection. It opens the door to foreign influence and corruption…” It’s safe to say he was not a fan.

So it’s with some trepidation that I want to speak up in favor of political parties. For well over 165 years, they have played a key role in our representative government. They are the best stage I know for broad economic, political and social change. It’s hard for me to imagine a democracy without them.

This is in part because we live in a very different country from the one George Washington led. The United States today is not just geographically bigger, but immeasurably larger in both population and diversity.

Our political parties play a lubricating role in the mechanisms of democracy

And that’s where our two great parties, for the most part, have excelled: They accommodate different interests, opinions and views. Our system does not have enough consensus-building mechanisms; the parties are crucial to this. Strong political parties that can unite groups with different interests have been a source of powerful change in our history.

Of course, more than building consensus within a party is needed. Even though the American people prefer bipartisanship, the parties too often prefer to lambast each other. But legislation passed on a party line vote rarely stands the test of time. To work properly, our system needs a broader consensus — and party-line votes do not provide it. The really effective legislation in our history — Social Security and Medicare, for instance — was passed with solid, bipartisan support.

Our parties also play a lubricating role in the mechanisms of democracy. They get out the vote and educate voters. They teach many thousands of ordinary Americans what the nuts and bolts of democratic participation look like. They choose, train and promote candidates who are (for the most part) worthy of holding public office. They play an important role in funding elections, financing the system and giving candidates a platform. In short, they’re a personnel system for government office.

To be sure, Americans divide rather sharply on their support of political parties — not just on which they support, but on whether to support them at all. Many avoid identification with them. Others become ardent loyalists. Still others follow them regularly, but not slavishly. At the moment, more people define themselves as independent than as a member of one or the other party, but the two parties together still command a majority of the electorate.

I am a member of a party and have certainly been disappointed in its performance on occasion. Yet I’ve never felt that my disappointment was grounds for abandoning the party. Nor, on the other hand, have I ever felt that my loyalty was grounds for despising the other party. I cringe when I hear a member of either party express hatred or accuse the other party of disloyalty. Both parties are patriotic, both want the best for their country — even if they have different ideas about what “best” means. That’s part of the democratic dialogue, after all.

That’s why I also get uncomfortable with unswerving loyalty to any political party. I think political parties have to earn our loyalty by their performance. And in particular, by their ability to move the nation forward legislatively.

George Washington was right, of course, in pointing out some of the risks of people joining together to form organized parties. But he didn’t fully recognize their role as consensus-builders — their concern with transcending differences and political factionalism and arriving at stances designed to appeal to political majorities both in elections and in legislatures. The most successful party officials I know have made consensus-building a priority, both within their own parties and across partisan lines. In a country as diverse and divided as ours, that’s not a baneful effect at all.

• Lee Hamilton is a senior advisor for the Indiana University Center on Representative Government; a distinguished scholar, IU School of Global and International Studies and a professor of practice, IU School of Public and Environmental Affairs. He was a member of the U.S. House of Representatives for 34 years.