Selecting the greatest player of all time (GOAT) is a semi-serious exercise by sports fans. Firstly, we have to decide on the criteria, which are seldom agreed upon universally. My criteria, as listed below, are likely stringent, for the reasons given therein. Secondly, one has to make certain assumptions. The most important one is that the overall, relative quality of players or competitions is the same across generations, even though players of the younger generations look clearly stronger and faster than those of the older ones. Such an assumption may or may not be true, but it is a reasonable null hypothesis.
My three criteria for a GOAT: 1. This player's achievements must be better than those of all the other greats in the history of the sport, or in rare cases, at least the same as the best of the class. Examples of achievements include Olympics gold medals, world championships, world cup championships, grand slams, and other, historically major competitions/titles in the sports. This criterion is obvious and accepted by everybody, although the details can be up to debate. 2. This player must have a good head-to-head record against all his principal rivals of the same generation as well as against those of an earlier generation and of a later generation, if a large sample size is available. This is a tough one, but it shows that this player is truly a transcending figure, pushing aside earlier greats, thoroughly dominating his peers, and then withstanding challenges from the young guns. A possible scenario is that if he keeps on playing for too long, he will lose to the younger players more and more. A solution is to set an arbitrary cutoff time up to the point when he is in the final of his last major title game, meaning that he is still competitive. 3. It is OK not to have a GOAT. Combining criteria 1 and 2 we will have many candidates with an overall excellent case for GOAT but also a glaring weakness, in any sport. In that case, since GOAT is really about a sport as a whole and the history of the sport and more than any particular game, any single player, or a generation of players, why don't we just leave the "sacred" title vacant for now?
With these tough but objective criteria, is Lin Dan the GOAT in badminton? (Since 1980, because before 1980 the badminton world was divided, so it is hard to argue for or against the players then.)
1. Define the achievements, slightly different from what the BWF says. Level I events are Olympics (OG), World Championships (WC), Thomas/Uber Cup, Sudirman Cup. Level II are All-England (AE), Asian Games (AG), team and singles. Level III: all the others. AE is ranked high here because of its longest history. Some of the events are for teams, but one can still consider the individual plays.
2. Let's define Lin Dan's generations or main competitors, one from each country and roughly based on when they first played in the Olympics. Of the same generation: Lee Chong Wei (LCW), Bao Chunlai, Park Sung Hwan. The previous generation: Peter Gade (PG), Taufik Hidayat (TH), Xia Xuanze, Lee Hyun Il (LHI), and Choong Hann Wong. TH and LHI can also be considered only half a generation older than Lin Dan (LD) or even the same. The younger generation: Chen Jin, Simon Santoso, and Jan Ø. Jørgensen.
If we look at LD's achievements (criterion 1), he is far better than anybody listed above, with one OG, AG (two teams and one singles), 4 WC, 4 AE, 4 Thomas Cups, 4 Sudirman Cups, all as the No 1 singles, and many other titles. The only person ever coming close in comparison is Yang Yang (YY). YY won WC consecutively and was a sure hand in Thomas Cup plays. In YY's time there was no Olympics badminton, although he won the exhibition in 1988, and only once Sudirman Cup, in which YY won his matches. LD's peak or domination is from late 2003 and still ongoing (2011), while YY peaked from 1986-1990.
Criterion 2 sets LD apart from YY and everybody else. YY had a bit trouble beating Zhao Jianhua, while LD dominates all his major rivals. For example, according to BWF, which does not count AG, the head-to-head record until 8/2011 against TH is 8:3, LCW 16:8, LHI 9:3, PG 15:3, SDK 9:1, and Chen Jin 11:5. Only the older Chinese Xia Xuanze has an OK record against LD.
So LD's case for GOAT is extraordinarily strong and airtight. He is truly the best ever. To put it into perspective, I don't think there is a clear GOAT in women's badminton. With Badminton being such a physically taxing sport, it is hard to imagine anyone could be so good for so long. We are lucky to witness LD playing at our times.
Note: LD's battle with LCW in 2011 WC was a dramatic match, high in intensity but low in beauty (relatively speaking), as both players made a ton of errors. LD made more at the beginning of each set but fewer at the end, which was why he won. There is nothing like fate or certainty that prevented LCW from winning. With some extra luck LCW could have won. But the place of LD in history was set well before 2011.