This is a tough one. The answer, as the Germans would say, is Jein–ie, both Ja and Nein, Yes and No (I guess that would be Yo in English). Let me illustrate what I mean with four examples out of many. These are people whose thought a) simplified enormous complexity and b) turned out to be wrong: Isaac Newton, Plato, Sigmund Freud, and Karl Marx (whom at least one of you has nominated).
Nein (1): The case of Newton
I hardly need to make the case that Isaac Newton was one of the greatest thinkers ever. While the plague ravaged England, this twenty-something went home to the isolation of his farm, used his imagination and reason, and gave us breakthroughs in understanding (wait for it)…. calculus, light and gravity. That’s a lot for one or two years, you will agree. Only Einstein in his “miracle year” of 1905, would come close.
And yet: That same Einstein would, starting in that year, prove Newton wrong. The calculus was fine, but Einstein rocked our understanding of light and (more famously) gravity. It was far, far weirder than even Newton could have imagined.
And yet yet: Nobody, least of all Einstein, would ever entertain a notion as ridiculous as downgrading Newton’s contribution. Who cares if his ideas were incomplete, and thus wrong! Newton himself famously said: “If I have seen further it is by standing on the shoulders of giants.” Newton became the giant whose shoulder Einstein stood on. It is entirely possible that we will discover that Einstein was wrong too. Would that make him any less of a thinker? Hardly.
These thinkers are great because they shed progressively more light into the darkness of our ignorance. Being right in the sense of leaping ahead over all future generations is not part of the job description.
Nein (2): the case of Plato
Alfred North Whitehead, no slouch among philosophers himself, once said that all of western philosophy is but a series of footnotes to Plato. Why would he say such a thing?
Because Plato (or Socrates, if you believe that Plato mostly transcribed the stunning conversations of his teacher) raised pretty much every fundamental and intelligent question that mankind could ask. What is good? What is beautiful? What is just? What … is?
Once again, that is a lot. Coming up with the answers to all those questions was not part of the job description, especially since we have not figured them out yet 2,400 years later.
But Plato has been a lot luckier than, say, Marx, in that nobody ever thought to try his ideas out in practice. I think we can agree that none of us wants to live in a society such as the one in Plato’s Republic. Aldous Huxley’s Brave New World comes close to it. Thank god we never “tried Plato out”.
Ja (1): The case of Freud
Freud gave us some beautifully profound, stirring and simple thinking. Everything has to do with sex! How refreshing, after Marx had put everything down to money, and Nietzsche to power.
Well, the trouble is that these were all oversimplifications. To quote our man Einstein again,”Everything should be made as simple as possible, but not one bit simpler.” If you make things too simple, you end up looking just plain silly.
Which is what happened to Freud, and the one to blow his cover was Carl Jung, his disciple at the time. Promise me to make the sexual theory a “bulwark”, Freud once implored Jung. “A bulwark against what?” asked Jung, disconcerted. “Against the black tide of occultism,” said Freud. Jung realized at that moment that his mentor was no longer looking for truth but power (his own). Sex is a biggie, Jung admitted, but not the only thing that matters. And so he broke with Freud. He was excommunicated from the clique, but in time found his footing and became an infinitely greater thinker (if less famous) than Freud.
Ja (2): The case of Marx
We have already pinpointed Marx’s biggest oversimplification, which was to put everything down to production, and who controls “the means of it.” Tangible wealth and its distribution matter, but they are not the only thing. And this was a tragic flaw in Marx’s thought.
There were others: His theory of value was wrong. (It’s not how much labor went into something that makes it worth what it is, but what somebody else will be prepared to pay for it.) And so on.
And, I would argue, his view of human nature was wrong: Once “From each according to his abilities; to each according to his need” becomes the law of the land, you will very quickly find the ablest people demonstrating impressive “abilities” at proving their own “need”. The entire philosophy spirals downward into a glorification of envy, which is a base, not a noble, instinct.
Still, Marx made a huge contribution to human thought, and if we had not tried him out–who knows?–we might rank him up there with Plato.
The conclusion is that being wrong must not disqualify a thinker from being nominated for the title of “greatest”. But since that title implies a certain timelessness, being right cannot be entirely irrelevant either. As it happens, the person I am leading up to, I believe, was right.