Good thing we don’t have a Y2.02k bug to grapple with. I hate anomalies.
Well, the question as stated in the thread title is unambiguous to me: The 2020s started 1/1/2020. There is absolutely no question or argument about this. The 203rd decade, though, technically starts on 1/1/2021. That’s not the 20s. That’s the 203rd decade. It’s a named decade vs an ordinal number.
The 21st century technically started 2001. However, phrased as “this century” or “our current century” (as in the OP and not the thread title,) I can entertain the idea that we’re not looking for the ordinal start of the 21st century, but rather the start of the 2000s. In that case, 1/1/2000 is perfectly fine defined as the starting point of the 2000s (as a century.)
Now, we can certainly say “to hell with it” and define the first century as 1-99 instead of 1-100 and then we can all stop arguing about this, but I doubt they will happen. As it stands, if a century is referred to ordinally, it starts in a year beginning with “1.” Same with decades, but decades are generally not referred to ordinally. They’re named cardinally, so it’s in that cardinal range of ten. Phrases like “this century” can be ambiguous. The 2000s, if referring to the decade, are 2000-2009. Referring to the century, it’s 2000-2099. The 21st century, though, is 2001-2100.
And what about that kooky 5th Dentist???
I agree with the OP, but there’s no inconsistency. The 21st century began on January 1, 2001, but the 2000s began on January 1, 2000. Two different things.
For those who argue that a century has to be a exact length of time, how do you handle the calendar shift?
The calendar designed by the ancient Romans was not precise in measuring the length of a solar year. It was based on the assumption that a solar year was 365.25 days long. This meant that every fourth year, you had a leap year of 366 days to keep your calendar in line with the physical years.
But a solar year isn’t 365.25 days long. It’s 365.24255 days long. And that meant that every calendar year was a little bit longer than the solar year. And over the centuries it added up.
In 1582, Pope Gregory XIII decided to fix this. He introduced a new calendar which had fewer leap years. And then to bring the new calendar in line with the physical year, he cut ten days from the year 1582. October 4 was immediately followed by October 15.
But many countries did not recognize the authority of the Pope and refused to adopt the new calendar for many years. Britain didn’t adopt it until 1752. Russia didn’t adopt it until 1918 (which is why the October Revolution started on November 7).
This means we had a century that was ten or eleven days short (depending on when the new calendar was adopted). So do people who believe centuries are exact measurements wait until January 11 to celebrate the New Year?
Speaking of New Year’s Day, it used to be celebrated on different days. Some places started the new year on December 25. Some on January 1. But the most common date was March 25. (This is why we have months named September, October, November, and December - they used to be the seventh, eighth, ninth, and tenth months of the year.)
Gregory decided that the year started on January 1. That meant that in some places the year 1582 began on March 25 and ended on December 31. And like his other reform, this was not immediately accepted by Protestant countries. England kept using March 25 as the first day of the New Year until 1752. This meant that if you had been in Paris on February 15, 1688, it would have been February 4, 1687 on that same day in London.
You’re all wrong! It’s the '80s!
5780, to be exact, on the Jewish calendar. 
On the Gregorian calendar, I am on the side of centuries/millenniums start when the last digit hits 1 (01/01/2001), but decades are a different measurement based on the third last digit (2020-2029 is the '20s).
Being more pedantic, 2020 is the preface of the decade, 2021-2023 are the early '20s, 2024-2026 are the mid '20s and 2027-2029 is the late '20s. And the same for every other decade by extension.
It’s really simple.
The 20th century ran from 1901-2000.
The 1900s ran from 1900-1999.
Same way with decades. The 2020s are the years 2020-2029.
“The third decade of the 21st century” would be 2021-2030, but nobody ever talks like that.
When most people are thinking of the '80s, they’re not thinking of 1990. They just aren’t.
I am. The 90’s started in December, 1991. The first Gulf War definitely partook of the militaristic triumphalism of the Reagan-Bush 80s, and the remnants of hair metal were not swept away until Grunge came in.
I side with noted Oxford-educated psychologist and respected federal law enforcement agent Fox Mulder: “No one likes a math geek, Scully.”
OTOH, when people think of The Sixties, they’re generally thinking of a period that begins roughly when the Beatles first come to America, and ends at some point in the early 1970s that varies* from person to person. But it’s the exception. Most decades, you can just go with the numbering.
*I personally draw the line just after the last major antiwar protest of the era - the May Day protests of 1971. But I’ve known others who drew the line between decades at Nixon’s resignation in August 1974. Like I said, it varies.
Ditto.
Nope. It’s no more “technically correct” than prescriptivists who claim words in the English language “technically” mean something other than the way people actually use them.
Ordinality has nothing to do with it. You have ordinality (1st century, 2nd century, etc.) whatever date you deem to be the beginning & end of each century, and whatever the apparent precise length of each century that implies.
The repeated assertion that the 21st century started on Jan 1st 2001 is based on a flawed assumption that in counting centuries we’re concerned about the precise number of years that have elapsed since some vague reference date in the distance past. We’re not, and (per Little Nemo’s post above about calendar reform etc) if that were the case then we’d need to account for a lot of other factors too, and it would not be Jan 1st 2001 either.
When we think about moving into a new century, we’re not celebrating the fact that a precise number of years have passed since some poorly defined reference date, we’re celebrating the fact that a big number on our calendar system changing, giving us a sense of the broad passage of time. Everyone knows that, which is why this “technically” nonsense was always dismissed with a roll of the eyes.
You’re not “techically” right, you’re just wrong.
The 20s begin in 2020, but I spent too much effort working on Y2K issues to believe that the 21st century began in 2001.
The 1920s ended when the stock market crashed. The 1930s ended with the start of WWII. The 1950s began with the Berlin airlift in 1948, and the 1960s began when JFK was shot. Now get off my lawn.
Regards,
Shodan
It’s the 20’s and THANK GOD. This “aughts” and “tens” business has been really awkward and I didn’t like it. It is a bit weird though to be “reusing” a decade that seems fairly recent and famous though. I love pretty much everything about the OG 20’s except the depression.
The XKCD brushes on the cardinal vs. ordinal thing.
Take ages. You are one year old during your second year of life.
As mentioned above, this means that there’s a “one off” in the numbering of years/decades/centuries/millennia vs. the order number of years/decades/centuries/millennia. So the 20’s started yesterday. The third decade of the 21st century starts in 365 days. Since the later type of reference is rarely used, the chance of confusion is lessened compared to the centuries/millennia issues.
The 2020s are any year where you read it ‘twenty twenty whatever’.
The decade that starts on 01/01/2021 is ‘the third decade of the 21st century CE’.
Also, forget ‘other - please explain’…Please explain if you chose ‘this isn’t the start of the 2020s’ but also chose ‘the 21st century started in 2000’.
Except possibly the odd historian. Historians don’t usually think in terms of finite dates, but rather in eras, e.g., study of the 19th century America usually starts in about 1812 and ends in about 1917. 
I voted ‘other’.
The 20s started 1-1-2020.
The century (and millennium) started either 1-1-2001 or 1-1-2000, depending upon whether using the ‘century’ as ordinal or cardinal numbers, respectively. (Personally, I’m a ‘cardinalist.’)