Who is the greatest chess player of all time ?? Bobby Fischer ??

Don't get me wrong, it was even better than "good enough". 

But there's a difference between good enough and unbelievable. 

Also I don't think there's any evidence to suggest that Smyslov at 63 (2600) was stronger than Petrosian at 42 (2640), or that Korchnoi at 52 (2610) played better than Larsen at 36 (2660). Heck, even Taimanov had a higher rating in 1971 than any of the 3 players Kasparov faced in the candidates matches.

As for world championship matches, Kasparov never defeated anyone by a 12.5-7.5 margin, unless you consider the match with Short a true WC match (in 1993, Short was 2665 and #12 in the world).

I can go on but no need to labor the point: as far as peak strength is concerned there's a case to be made for both Kasparov and Carlsen (though I believe the jury is still out), but when it comes to dominance, nobody can touch Fischer. 

"I don't think there's any evidence to suggest that Smyslov at 63 (2600) was stronger than Petrosian at 42 (2640), or that Korchnoi at 52 (2610) played better than Larsen at 36 (2660). Heck, even Taimanov had a higher rating in 1971 than any of the 3 players Kasparov faced in the candidates matches"

So how did Fischer do in his first two candidates compared to how Kasparov did in his first? :-) 

"As for world championship matches, Kasparov never defeated anyone by a 12.5-7.5 margin, unless you consider the match with Short a true WC match"

Why wouldn't it be considered a true WC match? Short qualified by winning the FIDE Candidates where he won a match against Karpov. Then it's difficult to compare beating Karpov in matches with beating Spassky. And is for example Alekhine's beating Bogo 15.5-9.5 more impressive than his beating Capablanca 18.5-15.5 just because he scored a bigger plus against Bogo? Fischer won 12.5-8.5 against Spassky, but Kasparov's beating Short 12.5-7.5 doesn't have to be the more impressive result just because he won easier.

Define "time". Then define "all time". Do you include future in "all time"? Do you include engines in the set of chess players? Please be more specific.

I was tempted to say "let's not change the subject" but fine, let's have that

First of all, Fischer's allegations of prearrangement in Curacao (unlike other bizarre allegations he made over the years) are now considered factual even by former soviet players. 

Second, both 1959 and 1962 candidates were round robin tournaments, not knock out matches.

Third, you have to consider the level of opposition. If you think Beliavsky and Korchnoi in 1983 were stronger than Tal, Keres and Petrosian in 1959 and 1962 respectively, go ahead and state your case. But I hope we can at least agree that Smyslov was a more formidable opponent at 38 than 63.

Collusion, tournament format and opposition aside, it's probably fair to say that at 17-19 Fischer was less dominant - on those occasions at least - than Kasparov at 20-21 (after all, he started playing chess a bit later than Kasparov and had far less support). The reason I stated "on those occasions at least" is because Fischer won the 1962 and 1970 Interzonals by larger margins than Kasparov (who actually won a split interzonal without having to deal with Ribli and Smyslov). 

Why wouldn't it be considered a true WC match?

It's not a question of true/untrue, it's one of significance/relevance. Fischer scored 12.5-7.5 against the reigning world champion (#2 rating wise). Kasparov won by the same margin against a challenger who was #12. When pitted against #2, Kasparov never won by more than 2 points.

"Fischer's allegations of prearrangement in Curacao (unlike other bizarre allegations he made over the years) are now considered factual even by former soviet players"

Fischer lost lost 3 of his first 5 games, and 5 of his first 13 games. I don't think anyone seriously thinks some short draws between Keres and Petrosian was the cause of that. He just played far from well enough and finished three points from a top three spot. Petrosian didn't lose any games in 27 rounds. After 21 rounds Fischer had lost 7 games, Geller and Keres taken together lost one game in these 21 rounds. 

"both 1959 and 1962 candidates were round robin tournaments, not knock out matches"

That's true, I have no idea how that affected the outcome though. Fischer scored a minus in his four games against Korchnoi in Curacao, but finished 0.5 ahead in the tournament (not a big margin if Fischer is to be believed that Korchnoi threw lots of games in the event...).

"If you think Beliavsky and Korchnoi in 1983 were stronger than Tal, Keres and Petrosian in 1959 and 1962 respectively, go ahead and state your case"

That they certainly weren't (even if Korchnoi isn't to be underestimated, he was #3 as late as in 1984 and #5 in 1989, while Beliavsky was #3 in 1985), but then Kasparov won against them with a big margin instead of finishing far behind them.

"Why wouldn't it be considered a true WC match?

It's not a question of true/untrue, it's one of significance/relevance. Fischer scored 12.5-7.5 against the reigning world champion (#2 rating wise). Kasparov won by the same margin against a challenger who was #12. When pitted against #2, Kasparov never won by more than 2 points"

Fischer's 12.5-8.5 against Spassky is difficult to compare with for example Kasparov's match wins against Karpov. No one considers Spassky to be in the same league as Karpov. Tal scored the same 12.5-8.5 against a reigning World Champion as Fischer did, but I don't think he is anywhere close as great as Kasparov.

Fischer-Spassky, 12.5 - 8.5 yes, but, if you consider the 1st game, Bobby's 29th move Bxh2, blunder or some way to create complications, it doesn't matter give it to Borris. How about game 2 though? Forfeit. could have been 13.5-8.5 or 12.5 - 9.5, either way we'll never know. This has probably been mentioned but, how about the 6 - 0 whitewashing of Taimanov and Larson in the candidates and a win in the first game with Petrosian, then a loss, 3 draws and four straight wins? A couple of famous Grandmasters once said, "Even when your ahead of him you know you're going to lose" and "He can toss the pieces up in the air and they land on the right squares". Things change, technology changes, but we can only compare Bobby to his contemporaries.  

Difficult, but still somewhat relevant.

Look, we can't have it both ways. Either ratings aren't stable over time (in which case arguments like "Carlsen and Kasparov are stronger than Fischer because they had higher ratings" can be called into question), or they are stable over time, in which case comparisons based on ratings and performance ratings are to a certain extent possible.

Between 1985-1990 (the era of Kasparov-Karpov titanic struggles) Karpov's rating fluctuated between 2700 and 2755, some 40-95 rating points higher than Spassky's 1972 rating. Now I know Spassky has been the target of a variety of insults over the years (mainly because of catering to Fischer's demands and "handing over" the crown), but speaking strictly in terms of performance, I doubt you'd refer to somebody within 100 rating points of yourself as being in a different league. 

Finally, for those interested in that kind of stuff, here's a summary of performance ratings for the WC matches of 1972, 1985, 1986, 1987, and 1990.

And for reference also the candidate matches that lead to these:

Looking at these, it's becoming clear that the old saying "Fischer was more dominant because he faced weaker opposition" is at best a half truth. It's true when referring to the one and only WC match he played, and even then his performance rating was still higher or same with Kasparov's in any of the 4 K-K matches. But in the candidate matches the picture is clear: not only was Fischer's opposition somewhat stronger, but his performance was well beyond what would have been expected based on the rating difference.

I'd say the brilliant sacrifices and intuitive combinations by Mikhail Tal make him the best. He treated chess as an art, not a science.

Especially since Short wasn't even close to Spassky's level.  Also, Fischer forfeited one of his games vs Spassky, so technically it was 12.5-7.5.   

I think people often value achievements based on which players they like. In tennis few would say that Player X was the greatest, among other things because he scored 6-0 6-0 6-0 in the quarter final, even though he only won a Grand Slam event once. If Player Y won Wimbledon eight times, even if he did it by scoring 3-2 in sets in every match he played, I think almost everyone would consider Player Y to be greater. If Player X was comparatively better than his competitors the one time he won would be considered rather irrelevant. 

In chess I think it is Fischer that has caused many to evaluate greatness not in how many top events the players won, but in distance to #2 at one point in time. This measure makes Topalov greater than Anand and Kramnik, and Morozevich (who was #1 one day on the live rating list...) greater than the Korchnoi of the 1970s, who lost two matches with the smallest possible margin against Karpov. Fischer is of course a case that is different compared to many others, but it is rare to see other players evaluated with the same measures. 

Carlsen has probably caused many to evaluate greatness as having the highest rating, and that is even worse... Having a higher rating today than some player from the past doesn’t say much about greatness in itself. Radjabov may have reached a higher rating than Fischer and Karpov, but his achievements are not anywhere near to make him comparable to them with regards to greatness.

Who the heck is Radjabov?   Isn't that the guy that beat Kasparov once, with a knight sac?   He isn't even in the top 500 of all-time.  You have a good point with the tennis comparison though.  I don't hear anyone saying that Bjorn Borg was better than Federer, Sampras, Nadal or Kjokavic, even though Borg dominated for a short time.  

I must say I have absolutely no idea about tennis so I'm honestly asking: would such a result (in tennis) have the same significance as Fischer's victories over the 3 best players in the world?

Another way of asking this: would anybody write something similar to the following about a player who scored 6-0 6-0 6-0 in the quarterfinals? 

"Who would have imagined that any challenger's match would ever have been decided by a perfect score, when the participants are all to be ranked among the strongest players in the world?"

"It is difficult to portray to non-chess players the magnitude of such a shutout. A typical result between well-matched players might be, say, six wins to four, with nine draws"

"To a certain extent I could grasp the Taimanov match as a kind of curiosity–almost a freak, a strange chess occurrence that would never occur again. But now I am at a loss for anything whatever to say... So, it is out of the question for me to explain how Bobby, how anyone, could win six games in a row from such a genius of the game as Bent Larsen"

"No player has ever shown a superiority over his rivals comparable to Fischer's "incredible" 12–0 score in the two matches"

”Who would have imagined that any challenger's match would ever have been decided by a perfect score”

”It is difficult to portray to non-chess players the magnitude of such a shutout. A typical result between well-matched players might be, say, six wins to four, with nine draws”

Ivanchuk once won all the games in a Candidates match up until the last one, where he took the draw being piece up (a draw was sufficient to end the match). If he had won also the last game I don’t think anyone would have cared particularly...

"No player has ever shown a superiority over his rivals comparable to Fischer's "incredible" 12–0 score in the two matches"

Possibly if you talk about superiority over Taimanov and Larsen in these two matches, otherwise it is quite a subjective subject. Steinitz scored 7-0 without draws in a match against #2 Blackburne, and won 25 games in a row against top opposition. Fischer scored 12.5-8.5 against #2 Spassky, and that was impressive enough. But if that was some sort of uncomparable superiority depends on what player one likes, and which results one counts.

Let me tell you something you already know: you'll struggle to find a WC or any other top GM whose merits are not exaggerated, especially in the context of a comparison, and especially from the critic's point of view. 

It just so happens that some people are more mesmerized by a guy who can lift 200kg once (when everybody else can lift only 150kg), than a guy who can lift 180kg for 10 years. Nigel Short put it better than I can when he said: He [Kasparov] is the greatest player in chess history, in my opinion. He had a much longer reign than Bobby Fischer, though Fischer probably shined brighter for a short period of time.  

Kasparov no doubt has had the longest tenure at the top (even more significant than Lasker's for a number of reasons), but one tends to forget that his titanic battles were against the same opponent over and over again. In that sense, every new K-K felt - to some - as some sort of "Kasparov - Karpov reloaded" affair, especially since he didn't necessarily win the next match more convincingly than the previous. Short and Anand were strong respectable players, but only about #12 and #6 respectively at the time those matches took place. And against Kramnik well... he lost that one without a single victory. 

Go on any chess forum, and you won't have much trouble finding a dozen users who claim "boy, if only Kasparov had to deal with the same patzers Fischer played, he would have wiped the floor with them". Well, as it turns out he wiped the floor with Short exactly the same way Fischer did with Spassky: 12.5-7.5 (rating wise at least, Spassky of 1972 and Short of 1993 were pretty well matched i.e. 2660 vs 2655). It's not like Kasparov was winning by the same margin against a guy rated 2785 or higher. 

Another example is the 'Massacre in Meran', which refers to the Karpov Korchnoi rematch. Yet when looking into it objectively, Karpov won by a smaller margin than Fischer did, against a 50 years old guy . When is the last time you've heard somebody speaking of the 'Massacre in Reykjavik'?

”one tends to forget that his titanic battles were against the same opponent over and over again”

That doesn’t exactly make it easier when that same opponent is Karpov... But I don’t think one should just count title matches, Kasparov scored great results in the strongest tournaments decade after decade. He had a ten year period during which he never finished behind another player. His results against top players like Leko, Gelfand, Shirov, Morozevich, Grischuk and Adams was something over 40-0 in wins, and the first three of those players won the Candidates. So it isn’t just ”he only won against Karpov”.

”Karpov won by a smaller margin than Fischer did, against a 50 years old guy”

Korchnoi wasn’t just ”a 50 years old guy” :-) He was an incredible player also at 50. And if one should make such comparisons one could just as well say that Karpov scored a higher percentage in his match against Spassky than Fischer did, or that Karpov scored better against Korchnoi than Fischer did. But I don’t think such comparisons necessarily say much.

You have to remember, when making these assessments, that more recent players have access to more modern resources. Deeper opening theory, greater libraries of chess games, and - the big one - phenomenally strong engines to learn from. Even seemingly minor factors like the improvement in the top players' lifestyles have an impact. So testing various players' moves' accuracy with AlphaZero is not a fair comparison - Carlsen has had the chance to study how AlphaZero plays positions, and internalise the patterns in its play. Fischer had no such opportunity.

Nor can you just look at players' win records. Players from different eras faced different opponents. A player in a time where strength in depth in chess was low would enjoy an unfair advantage under this criterion.

I think the best way of looking at it is to ask "which individual player improved the overall standard of top-level chess the most?" And I think you have to go back further than most posters here have done. To my mind, the best player ever is Capablanca. He revolutionised endgame theory, and pretty much invented hypermodernism - a school which was so successful that his long, long unbeaten streak (eight years, I think) was finally ended by another player, Reti, who had copied his style. Imitation is the sincerest form of flattery.

I think you meant Stockfish.  AlphaZero is not available for analysis.  Also, I'm not 100% sure but I think that Nimzovitch "invented" hypermodern chess, not Capablanca.   

Thanks Alinfe.  This is just about the most solid argument I've seen.

Performance ratings in matches often don’t say that much about the greatness of players. If a 2800 and a 2600 play a match with all draws the TPR claims that the 2600 player played 200 Elo stronger than his opponent, even if they obviously played on the same level.

When Anand drew his 12 game title match against World #20 Gelfand his TPR was higher than Kasparov’s when winning the title match against Karpov in 1986.