Poltical Science: Poltical Parties why does the professor say this:

M: At the heart of the system of government called "democracy" is the institution of elections. The electoral system is the basic machinery by which popular government is exercised. And at the heart of the electoral system are political parties that organize voters and compete for support on issues. Participating in democratic politics means joining or supporting a political party. It means taking sides on central political issues. Political parties are the mechanism for selecting candidates and gaining support at the polls. Parties vary significantly in different countries,  but all parties have certain common features. Political parties are voluntary organizations,  generally national in scope,  made up of people who agree to some degree on public policies. In the United States and Canada,  political parties are stable,  and each party tends to embrace a wide range of views and interests. The democratic institutions of these countries operate essentially on a two-party system. Why a two-party system?
Or, should I say why has the two-party system prevailed in so many democratic states? For one thing,  the essence of politics is debate; there must be someone to debate with. A one-party system means one party monopolizes power and talks only to itself. A one- party system can only be totalitarian, and therefore quite distinct from democracy.
   Yes, Sandra?
W: Isn’t it true that another reason we have two parties is because, uh, because liberal and conservative attitudes are basic human—uh, I mean they’re a basic part of our nature. In fact, almost everything that we think or do seems to come down to having—to there being two different ways of seeing the world.
M: That’s an interesting idea. We even have the saying, "There are two sides to every coin." In every democratic society, there are generally two dominant parties—one for each side of the coin. In the United States, it’s the Democrats and the Republicans. In Canada, it’s the Liberals and the Conservatives. In both countries, the two parties are balanced enough so the minority party can become the majority by gaining an additional small share of the votes. The two parties have lasted so long because they have the ability to adjust to changes in events and in public opinion. But in addition to the two major parties, there are also several smaller parties on the margins of political power. There are lots of political factions that sometimes compete at elections. Parties are closely associated with various pressure groups, interest groups, lobbies, occupational organizations, and other groups that want to influence the decisions of the state. The purpose of each major party is to capture the legislative and executive organs of the state in order to get the party’s policies accepted. The aim of parties is to win elections. However, winning an election isn’t the same thing as capturing the power of the state. What really happens is, the state captures the winning party. Why is this? Well, for one thing, the experience of government tends to soften the contrasts of political debate. Government is a responsible business, while politics is a game with teams competing for victory.
W: Excuse me, Dr．Reed, but isn’t it—I mean, then what you’re really saying is, government and politics aren’t the same thing. You said that government is a serious business, but politics is like a game.
M: Right! Politics is a game. In politics, teams and individuals take risks, and there are winners and losers. Competition is the essence of politics. But with government, collaboration and compromise are necessary because the job has got to get done. So, why do we need political parties? We need parties because, for one reason, the process of policy formation takes place there. Parties maintain research offices and establish connections with press and citizens groups. This is how political parties develop information and thinking on major issues. The major parties retain enough differences so they can appeal to different groups of voters, and so they can offer alternatives to the independent voters who don’t vote purely on the basis of party loyalty. However, the party platforms tend to balance each other in the types of issues they take up. For example, when one party introduces a plan for education reform,  the other party generally takes up education as well.