Now that is a very good question but in light of the surge in the voter registration for Independents one must re-phrase the question to How do I know if I am a Republican, Democrat or Independent? You see, just this past spring the number of Independents surpassed the number of either Democrats or Republicans in America for the first time in the last 100 years.
Roughly speaking there are now about 40% Independents, and 30% Democrats and Republicans. If you are an Independent you are not responsible for the political nonsense in Washington because your party has not been in charge the last century. Free of blame you are also free to condemn all the crooks in Washington.
Of course it is also true that Independents gave the margin of victory to Obama in the last election so you really aren't completely off the hook for blame. Another problem for Independents is that every party or group from conservative to progressive, radical to just plain nuts, has no other place to go so they are part of your group. Just look on the ballot at all the splinter groups listed as Independent of the two main parties.
That means there is no common platform other than most Independents think the best government is no government, they want a balanced budget, no more national deficit, and get government out of their lives. Things like regulations and laws, taxes and fees drive them nuts.
Democrats seem to like fees, higher taxes, more deficit spending and a big fat federal government. They would rather reduce individual liberty than let maniacs have guns, or free speech if it is opposed to the Democrat party line. They love unions though many have no idea what happens to all the union dues paid. Most lawyers seem to be Democrats though they may work for Republicans.
Socialists are Democrats though Democrats may not be socialists. Liberal advocates are Democrats like the Civil Liberties Union who have sued to get God out of America though most Catholics are also Democrats who kind of like having God around. The means both pro-abortion and pro-life advocates are Democrats as well who seem to cancel each other out in elections.
Of course a lot of Conservative Republicans are also pro-life so one wonders why so many Catholics are Democrats. Just about all Blacks are Democrat though it was the Republicans who freed them from slavery under Republican President Abraham Lincoln. As for Hispanics, illegal immigrants would be Democrats if they could vote but most Cuban Hispanics are Republican because the Democrats gave away Cuba to Castro and Communism.
Anyone oppose to big government, deficit spending or increasing the national debt is a Republican because there is no way the Democrats can please all the radical factions that demand more money for their pet (special) interest. If you believe in cradle to grave care (socialism in other countries) you are Democrat but if you believe in making and keeping your own money you are Republican.
Republicans most likely are strict civil libertarians while Democrats often want to coddle criminals in the interest of criminal rehabilitation which causes the Republicans to make sure we can all own guns to protect us from the people who should be in jail or institutions.
Corporate fats cats used to be mostly Republican until Democratic President Clinton started acting like a Republican and passed the NAFTA act and other big business friendly bills and a bunch of Democrats became fat cats themselves. President Obama claimed to be the innocent outsider though he was the first Democrat to get more money from fat cats than the Republicans. Two years later his legislative agenda seems to have driven the corporate world back to the Republicans, ever since he and sidekick Joe Biden declared war on corporations and small business.
Independents are those mostly silent Americans who have watched the two parties and their schizophrenia and decided there just wasn't any difference between the Democrats and Republicans and wanted nothing to do with either political group.
Perhaps after reviewing the differences or similarities between the Democrats and Republicans, we should not be talking about a third party Independent movement but just get rid of the first two parties.
Sometimes the simplest solutions are the best. Or many we all need a ballot choice of "None of the Above!"
Besides, Democrats and Republicans are not specified in the Constitution or Declaration of Independence so why do we treat them as some type of privileged class?