Every time someone struggles to explain or select a racial identity, every time we have a public debate about should check get to check box, and every time a person's looks don't seem to match up with what they call themselves, it's a reminder that race is a social and political construct.

But what does that actually mean?

It means that racial categories are not real. By "real," I mean based on facts that people can even begin to agree on. Permanent. Scientific. Objective. Logical. Consistent. Able to stand up to scrutiny.

This, of course, does not mean that the concept of race isn't hugely important in our lives. Although race isn't real, racism certainly is. The racial categories to which we're assigned, based on how we look to others or how we identify ourselves, can determine real-life experiences, inspire hate, drive political outcomes, and make the difference between life and death. But these important consequences are a result of a relatively new idea that was based on shaky reasoning and shady motivations. This makes the borders of the various categories impossible to pin down and renders today's debates about how particular people should identify futile.

If you have any lingering belief that the racial categorizations we use make any real sense, read this and change your mind:

1) Americans embraced the idea of race to make slavery feel okay

Racial classifications didn't always exist. Of course, there were always people in different parts of the world who had some physical traits in common, but they weren't forced into rigid categories. Discrimination and stereotypes existed, but they were based on country of origin, religion, or culture, not so-called scientific distinctions.

With the 1776 edition of his book, On the Natural Variety of Mankind, German scientist Johan Friedrich Blumenbach is credited with creating one of the first race-based classifications. He decided on five categories: "Caucasian, the white race; Mongolian, the yellow race; Malayan, the brown race, Ethiopian, the black race, and American, the red race."

It's the basis of a manmade strategy for making sense of treating some people better than others.

Americans bought into this idea, too. Why was it so appealing? "Americans of European descent invented race during the era of the American Revolution as a way of resolving the contradiction between a natural right to freedom and the fact of slavery," historian Barbara J. Fields explained in a presentation to the producers of PBS's series Race: The Power of An Illusion (which is worth checking out for more detailed information on all this).

If "whites" were in their own category — with innate differences backed by science — then that category could be deemed superior. As a result, they could justify their own rights and freedoms while enslaving, excluding, and otherwise mistreating people who had been placed in different racial categories.

So the division of people into groups based on general geographical origins of their ancestors or descriptions of the way they look, is the basis of a manmade strategy for making sense of treating some people better than others.

2) The way we legally define different races in America can change on a whim — and it has

If race were based on permanent, innate divisions of human beings, the American government wouldn't have to constantly scramble to change the definitions and qualifications for each category.

But it does. All the time. As political priorities change, American racial definitions adjust right along with them.

So, for example, people of Mexican birth or ancestry were "white" until the 1930 Census snatched that privilege back. Since then, their status — white or Hispanic — has flip-flopped several more times, all depending largely on whatever the current thinking was about their role in labor or immigration.

Similarly, courts went back and forth in the early 20th century about whether people from Japan were white, finally deciding in 1933 that they weren't, based on "the common understanding of the white man." (Sounds really official, huh?)

And what it took to be "black" once varied so wildly throughout the country (from one-quarter, to one-sixteenth, to the infamous one drop of African ancestry) that people could actually change races by crossing state lines.

Then, suddenly, in 2000, the government decided that Americans could be more than one race, adding options to express this to the Census. In other words, one day you could be a single race, and the next day you could be as many as you pleased.

With these constant changes, it's hard to make the case that the concept of race is anywhere near stable.

3) Once upon a time, some people from Europe were "not quite white"

Today, the term "European" is treated as largely interchangeable with "white" in America. But that wasn't always the case. According a timeline published as part of the Race: The Power of an Illusion series, when immigration to the US from Southern and Eastern Europe increased in the late 1800s and early 1900s, many of the new arrivals worked low-paying jobs, were clustered in urban ghettos, and were seen as "not quite white." In fact, Germans, Greeks, Irish, Italians, and Spaniards have all — either legally or as matter of public opinion — been excluded from the "white" category at some point.

Germans, Greeks, Irish, Italians, and Spaniards have all — either legally or as matter of public opinion — been excluded from the "white" category at some point.

Today, the "white" census category is available to "a person having origins in any of Europe, the Middle East, or North Africa." History proves that that list was heavily informed by various groups of immigrants' popularity, not biological differences.

4) The government still hasn't figured out a good way to get people to pick a race

The US Government uses the Census to determine the official racial makeup of the nation. That's important information because, although the idea of race has no biological basis, the various groupings we've embraced now shape social reality when it comes to law, public policy, and interpersonal interactions. There's no question about whether race informs Americans' experiences with education, employment, the justice system, and countless other measures. The data collected can help paint a clear picture of how that works.

But accurately polling an entire country full of people who have different ideas about race and what it means has been tough, bordering on impossible.

Accurately polling an entire country full of people who have different ideas about race and what it means has been tough.

"Increasingly, Americans are saying they cannot find themselves on Census forms," a Census Bureau official told the Pew Research Center in March. As many as 6.2 percent of Census respondents selected "some other race" in the 2010 survey.

As a result, the Bureau undertook what it called "the most comprehensive effort in history to study race and ethnic categories," hoping to convince fewer Americans to skip the racial identification question by the 2020 Census.

One proposed fix that's under consideration: to make "Hispanic" a race of its own, which means changing it from its current status as an ethnicity choice that can be combined with a selection for race or "some other race." The government's controversial goal is that many of the people who in 2010 selected "Hispanic" and then checked "some other race" will in 2020 choose "Hispanic" as their race, leaving fewer unanswered racial questions about the population.

5) The race of people of Middle Eastern and North African descent is in limbo at this very moment

In addition to the Hispanic question described above, the Census Bureau is currently taking into consideration the views of people of Middle Eastern and North African descent who have told the Census Bureau they don't want to be categorized as "white" any longer.

It's unclear whether the Bureau will get behind these changes and, if so, whether the Office of Management and Budget will approve them in time for the 2020 Census. But if the fix does take effect, plenty of people who are considered white right now won't be in six years.

6) Siblings with the same parents can claim different races

The occasional sensational stories in the "Black and White Twins: Born a minute apart" vein are really just overblown reports on siblings who, because of normal genetic variations, have different complexions. That the public feels empowered to declare that two infants born to the same mother and father are actually different races says a lot about how many people give racial identity more credit for being objective than it deserves.

But here's what's even more revealing: adult siblings who share the same parents are free to choose different racial identities when they fill out the Census or otherwise decide how to identify. One might be "black" while the other chooses "black, white, and Asian." Yet another kid from the same family could declare him or herself "multiracial." They might make different choices because of their different looks, different experiences, or different personal politics.

7) You're free to change your race over the course of your life, as many times as you want

Between the years 2000 and 2010, millions of people who said they were of Hispanic origin (remember, that's currently an ethnicity option, not a race option) changed their census selection for race from "some other race" to "white."

There are stories of people who decide to "come out" as black, shedding, or sometimes, still holding onto, their previous "white" or "Latino" identities.

They're not the only ones in this country who've made adjustments to their racial identities. There are stories of people who decide to "come out" as black, shedding, or sometimes, still holding onto, their previous "white" or "Latino" identities. Maybe these individuals make the switch because they learned something about their parents' background. Or maybe it's because they've just begun to think about identity differently.

You'll of course raise fewer eyebrows if your appearance is one most associate with your new chosen race (and, if you are a person of color, no declaration on your part will preclude you from experiencing prejudice), but if you decide to check a new box, it really doesn't have to make sense to anyone but you.

8) You can't tell by looking at someone what box they check or how they identify

Last year, NPR reported on a tiny town in the Appalachian foothills of Ohio, where, for the past 100 years, people have called themselves African-American despite the fact that many would say they appear to be white. (Check out the pictures here.) This is an extreme case, in which "racial lines have been blurred to invisibility" among an entire community. But the idea that someone might look one way and identify another way — or that they might be really hard to place in a racial category — is not unfamiliar.

It's why there was a public debate about whether MSNBC's Karen Finney could say she was black.

It's why there was a public debate about whether MSNBC's Karen Finney could say she was black, and why people are curious about whether actress Rosario Dawson declares herself black, Latina, or both.

These are individual and relatively unpredictable decisions because there's nothing about the concept of race that requires more of them.

9) Seriously, there's not even a consensus on Obama

A 2009 Pew Research Center poll, the results of which were published this year, revealed that 52 percent of Americans said Barack Obama was of "mixed race," while 27 percent called him "black." In other words, we can't even agree on the racial label assigned to the President of the United States.

10) DNA tests can't measure it

A DNA test can give you information about where your ancestors came from. That's not the same as telling you what your race is. The constant changes to whether people from various parts of Europe are "white" at any given time in United States history — including the one that might change with the next Census — are proof of that.

And while we're on the topic of science, Dorothy Roberts, the author of Fatal Invention: How Science, Politics, and Big Business Re-create Race in the Twenty-first Century explains that when the medical community links race to health outcomes, it's really just using race as a proxy for other factors such as where your ancestors came from, or what social inequalities people who have been grouped similarly to you tend to face. Here's how she put it in one interview:

There are studies to explain racial divisions in health that are actually caused by social inequalities. Yet you have researchers studying high blood pressure, asthma among blacks, etc. and looking for a genetic cause. However, research shows these [illnesses] are the effects of racial inequality and the stress of racial inequality ... Of those who say [race is biological], they usually point to sickle cell anemia, as proof that illnesses are race-based. Even if you look at these genetic diseases that seem to run along with race, it's actually caused by environment. Sickle cell is an adaptation in areas with high rates of malaria. You find it in some areas of Africa, Asia and Europe. It's not about race at all.

11) Race is impossible to explain to children

Try to explain to a curious kid why his mom, who has light skin, is "black," how we can tell for sure what race anyone is, or who decided on this handful of groupings of human beings, and you'll immediately realize how nonsensical it all is.