Who is the greater Olympian, Michael Phelps or Usain Bolt?

Definitively comparing athletes across sports is impossible. It’s also the quintessence of sports debate, tying in various tangential questions of how to quantify athleticism, skill and sporting greatness, and how to consider the merits of different games, competitions and achievements. And, most importantly, it’s wildly entertaining.

With Michael Phelps capping off a historic Olympic career with gold medal No. 23 on Saturday, and Usain Bolt gliding past Justin Gatlin for No. 7 on Sunday, one of these comparisons stares us in the face: Who is the greater Olympian? Phelps or Bolt?

[Related: Usain Bolt and the greatest 10 seconds in sports]

The debate rages on in bars and offices and cafeterias and sports talk radio studios across the United States on Monday. It might spread its way around the world too.

Strictly speaking, the answer is Phelps. His 23 golds are more than twice as many as any other Olympian. Phelps has more than three times as many as Bolt, though that could change if (when) Bolt gets his eighth and ninth in the 200 and 4×100 relay in Rio.

But the argument is deeper than those simple numbers, even if medal counts are the most apt quantification of Olympic greatness.

Phelps has competed in 30 Olympic events. His medal conversion rate is a remarkable 28/30, or 93.3 percent, and his gold medal hit rate is 23/30, or 76.7 percent. Bolt is even better. He missed once, as a 17-year-old in 2004. Since, he’s stepped into the blocks seven times at the Olympics. He’s won seven golds. He could make it 9/10, and 9/9 since his 18th birthday, within the week.

Bolt is also 3-for-3 in world records. He — and his Jamaican relay team — holds the best-ever marks in the 100, 200 and 4×100. Phelps, who has competed in and medaled in nine Olympic events, holds world records in six, though three are as part of relay teams.

Bolt has never not been the greatest since the 2008 Olympics in Beijing. Phelps, on the other hand, has been challenged in some of his events. He’s only won one gold and one bronze in the 200 free. He finished fourth in the 400 medley in 2012, and didn’t compete in the event in 2016. He got pipped for gold by Chad Le Clos in the 200 fly in 2012, and by Joseph Schooling in the 100 fly this past Friday.

[Related: Ranking all 23 of Michael Phelps’ gold medal races]

Phelps has the longevity and the multifariousness. Bolt has the indubitable dominance.

So what do we value? Do we value Bolt winning the title of “fastest man alive,” then doing it again, and again? Or do we value Phelps not only being the world’s best swimmer four Olympiads in a row, but swimming to that title by mastering four different strokes over three different distances?

One subjective argument says Bolt’s title is superior because of the elemental nature of running. Phelps does something that only around half of Americans can do: swim. The percentage is probably lower in other countries. The talent pool above which Phelps has to rise is thus significantly smaller.

Bolt, on the other hand, does something that the majority of the world does, or can do: he runs. He runs just like a high school soccer player does in competition, just like middle-aged men and women do to stay fit, just like 6-year-olds do on playgrounds. And Bolt does it better than anybody in the world ever has.

But Bolt does that one thing. He’s never stretched himself beyond the 200-meter race at an Olympic level. He’s never done the hurdles or the long jump. His agent even admitted that Bolt has never run a mile in his life. Some of this is out of his control, of course. The 400 and the 100 were run on the same night in Rio; Bolt wouldn’t be able to be at his best for both.

But still, Phelps’ repertoire is wider. He’s won multiple golds in 100s, 200s and 400s. He’s won golds in the freestyle, the butterfly and medleys. And he too must swim multiple races in a night. Most swimmers, like runners, have to specialize to reach the pinnacle of a certain stroke or distance. Phelps hasn’t done that, and he’s still better than those who have.

[Pat Forde: Why it’s time for Michael Phelps to call it a career]

Plus, although Bolt’s repertoire is limited by the nature of the events, there aren’t that many more swimming events (17) than there are running events (13). And while it’s not fair to consider Bolt’s events alongside the 3,000-meter steeplechase or the marathon, it’s similarly silly to look at Phelps’ events in the same picture as the 100-meter breaststroke or the 10-kilometer open water race.

To bridge the gap between the sports and their various events, a useful tool might be to compare Bolt and Phelps to the other athletes in their respective sports. Bolt is special because he’s won three Olympic 100s. Only one other sprinter, Carl Lewis, has won even two, and Lewis only crossed the finish line first in one of those. So in a way, Bolt is three times as great as the third-best 100-meter runner in history.

But Lewis ran and jumped to nine total Olympic golds. Medal count-wise, Bolt doesn’t even have the most gold medals in his sport. Lewis topped the world on at least one occasion each in the 100, 200, 4×100 and long jump. Here’s where Phelps still stands out. His 23 golds are 14 more than Mark Spitz’s 9. His 28 total medals are 16 more than anybody else in the sport.

Heck, if Phelps were a country, he’d rank third all time in Olympic swimming golds, behind the United States and Australia. Bolt would not rank in the top 20 in athletics. If we break athletics down into solely running events, he would probably crack the top 10. If we break running events down into only sprints, he would be somewhere around fifth or sixth. Regardless, Phelps stands out more when viewed through this historical lens.

So who is greater? And perhaps the greatest?

The debate as a whole is incomplete until Bolt’s Olympic career is complete. The Jamaican could still smash one or two of his own world records on Thursday and Friday. But even if he does, the scope of Phelps’ dominance probably eclipses the flair, forcefulness and perceived inevitability of Bolt’s.