The Big Question: So is Michael Phelps really the greatest athlete in Olympic history?

(Independent Graphics)

Why are we asking this now?

Because Michael Phelps, a 23-year-old American swimmer, yesterday won two Olympic gold medals in Beijing, one of them in the 200m butterfly race, and the other in the 4x200m freestyle, to take his tally at these Games to five, and his career total to 11. Nobody in the Games' 112-year history, in any sport, had previously gone beyond nine Olympic gold medals in their career. And Phelps may yet win three more gold medals before the swimming concludes on Sunday evening.

Phelps's feats in the pool have triggered an inevitable debate about what constitutes the supreme Olympic achievement, a discussion in which objectivity tends to go out of the window. There are umpteen contenders to be the greatest Olympian, many with deserving grounds for the title.

Like who, for example?

We can start with the quartet whose previous shared record of nine golds medals has just been eclipsed. One of them is Phelps's compatriot swimmer, Mark Spitz, who famously won seven golds in one Games in 1972 to add to two from 1968. Another is Carl Lewis, the American sprinter and long jumper whose nine medals arrived at four Games between 1988 and 1996. His versatility stands out. The other two are Paavo Nurmi, a Finnish runner who first won gold in the 1920s, and the Soviet gymnast Larysa Latynina, who amassed her medals between 1956 and 1964 after turning to gymnastics from ballet.

How can you compare achievements in different sports?

You can't really. If you use the only objective measurement of Olympic achievement – which is gold medals – then Phelps is "the greatest". He has 11 golds already. The quartet had nine each. Six other Olympians have won eight, five more have won seven, 13 have won six. Altogether 59 people have won five gold medals or more (five is the number of golds won by the rower Steve Redgrave, making him Britain's leading Olympian). There are a lot of contenders across lots of sports.

But do swimming medals come more easily?

No. Of the 100 leading multiple gold medal winners, 22 have been swimmers. There have been plenty of multiple winners in athletics and gymnastics, and quite a few in shooting and fencing. Aladar Gerevich, a fencer from Hungary, won six gold medals at six different Games. Birgit Fischer, a German canoeist, won eight golds at six Games. Some sports offer a few chances per Games over many years. Others offer more per Games but generally over fewer years.

Swimmers have relatively short careers, and few Games in which to win medals. And winning gold is not easy. Eight years ago, the swimming world thought that Australia's Ian Thorpe was the best, most naturally talented swimmer the planet had ever seen. He probably was, up to that point. But he ended up winning five gold medals in total at two Games and is now retired. Phelps is phenomenal to be so far ahead of his rivals in so many disciplines.

How goodis Phelps?

Beyond superlatives. In each of his five gold-winning events so far, he has set a world record. Then again, there are some who might argue that until he eclipses Spitz's feat of seven golds in one Games (in 1972), Spitz will remain the greatest Olympic swimmer, and maybe the greatest Olympian. It's also not possible for a rower, for example, to win multiple gold medals in one Games. Or a decathlete. The body, and scheduling, will not allow it.

So Redgrave can't be contemplated as the best ever?

Of course he can, and so can Britain's Daley Thompson, the decathlete who won gold medals in both 1980 and 1984. They are certainly challengers to be Britain's greatest Olympian, at least. Redgrave*s achievement in a horrendously taxing sport between 1984 and 2000 was momentous. Not least because he also had to cope with diabetes. Thompson won the greatest test of all-round athleticism on the track and field twice. And there are plenty of other contenders for best ever.

Such as who?

Well, if you're a hard-working mother, or even someone who appreciates a hard-working mothers, then Fanny Blankers-Koen might be on your shortlist. A Dutch mother of two, the "Flying Housewife" won four gold medals (sprinting, and over hurdles) at the ripe old age of 30 at the 1948 London Olympics, in an era when women's athletics was much derided.

Are those really grounds to be considered the greatest?

That depends on your definition of greatest. And that might depend on whether you place winning in a social context, or just consider the physical activity. By the former criterion, a lot of people, the greatest ever would have to be Jesse Owens, the black American track and field athlete who went to Adolf Hitler's propaganda-driven 1936 Games in Berlin and walked away with four gold medals. Like Blankers-Koen, winning four was a superb achievement in itself: he won the 100m, 200m, long jump and a relay running gold.

What if physical exertion is our criterion?

Even then, it's not easy to say which sport is "the hardest" or which multiple medallists in that sport therefore challenge to be the greatest. The inherent challenge of, say, running a marathon, is much tougher than running 400 metres. Runners over shorter distances can and do win more than one medal at a Games. Britain's Kelly Holmes did so in Athens in 2004, over 800m and 1,500m. But in general terms, more people qualify for the "easier" events, so the competition is tougher to actually win them.

And a lot of people swim, don't they?

Like running, swimming is a sport that is pretty much open to everyone, even though swimmers may struggle in some countries (like Britain) to find Olympic-sized 50m pools to train in. And though swimming is one of the most popular recreational activities in the world, and many thousands try to enter the Olympics every four years, relatively few ever get there. Fewer still win any medals, let alone gold, let alone 11 of them. Nobody, in fact, except Phelps.

Is it easier for swimmers to win medals?

Yes...

* Michael Phelps is swimming in eight events and lots of swimmers are similarly prolific

* The swimming events are basically similar, relying on the same rhythmic motor skills

* Most races do not last long, between 25 seconds and a few minutes as a rule

No...

* Just qualifying for the Olympic Games would be unachievable for most people

* Swimmers have relatively short careers that severely punish their bodies

* Plenty of other sports, notably gymnastics, offer chances to win lots of medals