Sufficient Reason

By Sean Carroll | November 23, 2008 12:28 pm

Dana McCourt at The Edge of the American West has a short series of posts on Leibniz and Spinoza, based partly on The Courtier and the Heretic by Matthew Stewart. This is great stuff, the kind of thing blogs do better than anything — bite-sized interesting pieces that stand by themselves, just because. (And the cheap chronological hook that November 18 was the day in 1676 when the two met in the Hague.)

All noble things are as difficult as they are rare.

The best of all possible worlds.

Why should we be loyal to reason if it pushes us into the abyss?

Scientists think of Leibniz as Newton’s rival in inventing calculus, and barely think of Spinoza at all. But they were both among the most influential philosophers of all time.

Leibniz published books and treatises, but much of what we know of his philosophy comes in the form of letters. I’ve joked that he invented the calculus on the back of a cocktail napkin in the corporate lounge while his flight from Paris to Hanover was delayed, and that of course was an exaggeration for comic effect.

It wasn’t the calculus, but a dialogue on theology, and it was on a yacht from London to Rotterdam that was held fast in port by headwinds.

The two men came started from different launching points, but ended up arriving at very similar philosophies.

Spinoza’s naturalism lead him to atheism, but Leibniz came to Spinoza via his theism. That is, Leibniz found himself desperately trying to come up with an argument that showed that his own philosophy was not threatened by the spectre of Spinozism, but his philosophical commitments, especially those concerning the nature of God, meant his options were limited.

Foremost among those commitments was the Principle of Sufficient Reason: the idea that nothing is “just because,” there is always an intelligible reason for everything feature of the world. It sounds innocent enough, but takes you to dangerous places if you buy into it with all your heart.

As far as I can tell, the PSR is not especially popular in respectable philosophical circles these days, but it is still hanging in there. It’s basically the foundation for Paul Davies’s claim that any respectable laws of physics must have a good reason for being the way they are. I don’t agree, myself; it might be true, but I’m very open to the possibility that the final product of our investigation into the ultimate workings of nature will be a set of rules that could easily have been different, but they simply are they way they are. At the very least, I would strongly defend the proposition that we should be open to this possibility; whether or not there is a small set of brute facts about the universe that lack any underlying justification, there is certainly no good reason to deny that scenario on the basis of pure thought, before we know what the ultimate rules actually are.

At a more casual level, the PSR shows up in the common belief that everything happens for a reason. That’s where the pernicious side of this purportedly sunny philosophy rears its head: if everything has a purpose, even the most terrible random events require an explanation, and from there it’s a short road to the urge to put the blame on someone. Or, on the flip side, to kill ’em all and let God sort them out. One day, when human beings have universally adopted an enlightened materialist view of the cosmos and have developed a corresponding system of ethics and morality, an important piece of the puzzle will be an acceptance of randomness and contingency. All is not for the best, in the best of all possible worlds, and that leaves it up to us to try to make things better.

  • John Faughnan

    Sean: “When human beings have universally adopted an enlightened materialist view of the cosmos and have developed a corresponding system of ethics and morality, an important piece of the puzzle will be an acceptance of randomness and contingency”.

    So do we get some kind of badge to put on our web site to indicate we’re members of the enlightened materialists?

    I’ve been using “enlightenment 2.0” as my tag:

    Maybe you could make us an icon? (Reminds me of the old days of webrings –

    Lloyd House ’81 (since sean knows cit)

  • Matthias

    Well then, I declare the Principle of No Reason. Everything is Just Because. Sorry guys, gotta sort out your lives for yourselves…

  • Christopher M

    Well, Gregory Chaitin claimed to have disproved the principle of sufficient reason. I don’t follow his field, so I don’t know the status of the argument within complexity theory, but here’s Chaitin’s Sci Am article from a couple years ago:

    If Leibniz had put all this together, he might have questioned one of the key pillars of his philosophy, namely, the principle of sufficient reason—that everything happens for a reason. …

    Mathematicians certainly believe in reason and in Leibniz’s principle of sufficient reason, because they always try to prove everything. …

    [But] certain mathematical facts are true for no reason, a discovery that flies in the face of the principle of sufficient reason.

  • Jacob Russell

    Everything has a reason…

    Everything has a cause… Which is it? What is meant here by “reason?”

  • steve from brisbane

    Sean, one might be less cynical of your anticipation of the glorious future under enlightened materialist philosophy if we hadn’t just come of a century in which we saw how disastrous some regimes with a materialist philosophy could be. I guess they just weren’t “enlightened” enough? Let’s face it, the pernicious side of “it’s up to us to make everything better” has been demonstrated to be the violent crushing of dissent if that is for the greater good of the majority.

    (I know that others will dispute this, but I also think that there is a strong argument that it is only from the “everything has a reason side” that the inherent value of every human life wins out over the interests of the majority.)

  • bane

    Steve from Brisbane,

    what you need to do is come up with some quantification of the inhumanities of materialistic philosophies and of various theistic philosophies, rather than just counting one side. There’s the one hypothesis that most human beings want to “convert” people to their views, whether it’s materialistism or some religious belief. (I guess the only difference I can see is that materialists crush dissent “for the good of the majority” whilst the religious do it “for the eternal salvation of those doing the dissenting”.)

    Human beings really don’t believe in live and let live except in those cases where “letting others live their lives” helps bulwark their own position.

  • chemicalscum

    After reading Satre’s Being and Nothingness I became convinced that the world was fundamentally contingent. It certainly made accepting the consequences of QM a lot easier.

  • chemicalscum

    Sorry spelling correction – Sartre not Satre. Must be typing faster than I think.

  • spyder

    I do very much recommend the Stewart book. It is particularly revealing of the life and times of a period, not so unlike our own, when major political, economic, and social upheavals were challenging the “way of life” (a century that began with the torturous burning of Giordano Bruno). Out of this chaos came stunning minds with powerful insights into the nature of our thought processes regarding the world around us. Given what was the available lake of knowledge (in comparison to our massive oceans today), Spinoza, Leibniz, Newton, Galileo, Huygens, Pascal, Harvey, Van Leeuwenhoek, and so many more expanded that relatively small lake into a vast sea of scope and vision (microscopy and astronomy pushing in and out our ‘envelopes’ of sight). Great philosophical minds worked hard to make sense of it all. I can only hope that over the next century, brilliant young philosophers will struggle has hard as Spinoza, Kant, Bacon, and Leibniz to make coherent the incredible, exponentially-expanding body of scientific knowledge being pushed forth into the cosmos.

  • steve from brisbane

    bane: I was really just trying to point out that Sean was only mentioning the pernicious side of the philosophy he doesn’t agree with. It’s only fair to mention that materialism has a “pernicious side” as well.

  • Bob

    oh great, Sean took modern philosophy..

  • Imam Yahya, Commander of the Faithful, etc

    “One day, when human beings have universally adopted an enlightened materialist view of the cosmos and have developed a corresponding system of ethics and morality, an important piece of the puzzle will be an acceptance of randomness and contingency.”

    A Zimbabwean friend explained to me that, in many traditional African societies, if someone gets sick it *must* be because a curse has been put on him by an enemy or someone working for an enemy. Basically, “anything bad that happens is someone’s fault”. He went on to describe the harm resulting from this notion.

    I told him not to feel bad about this: we have exactly the same superstition in the West. “Anything bad that happens to anyone is a result of their being *oppressed* by bourgeois capitalist etc etc etc.”

  • Lawrence Crowell

    I think Spinoza was not so much an atheist as he was an advocate of a God that was a purely metaphysical construct. Spinoza argued that what ever God there might be is one which did not act directly upon the physical world. He received considerable umbrage for this from the rabbinate. In Spinoza’s world view any moral requirement imposed by God existed through the physical world. Spinoza was an early thinker in the 17th century who argued that the operation of the physical world was independent of supernatural or divine action.

    Einstein remarked that if he believed in God it was the “God of Spinoza.”

    Lawrence B. Crowell

  • Daniel

    I’d agree with your suspicions regarding the so-called Principle of Sufficient Reason (at least in the vague sense in which I’m understanding it) in that it would seem to imply a type of infinite regress. If something requires a reason for “why” it’s the case, then every set of facts which constitutes its explanation would also require a reason, and so forth forever. Even if this were somehow possible in theory, it would be impossible for any human to understand the chain of reasoning required, and so at some point we simply have to accept things as arbitrary.

    “That’s where the pernicious side of this purportedly sunny philosophy rears its head: if everything has a purpose, even the most terrible random events require an explanation, and from there it’s a short road to the urge to put the blame on someone.”

    I believe this is an instance of the informal fallacy known as “argument from adverse consequences.” The fact that A implies B, B being anything unfavorable, (I’m not agreeing with you that it does here, only that your logic doesn’t make sense even if it did) does not mean that A is false, or even less likely to be true than otherwise.

  • Jason Dick

    I don’t quite understand why the Principle of Sufficient Reason couldn’t include the results of random processes? It just requires that we’re a bit careful about what we mean by a “reason” that something is one way instead of another. What this principle does, for a random process, then, is shifts the question from the specific observed outcome to whatever it is that generates the random process.

    So, if we want to talk about, say, why the cosmological constant takes the value it does, the answer might be that there isn’t any particular reason why it took this specific value, but instead it derives from a random process. And that random process itself follows a specific probability distribution because of the particular way in which new regions of the universe like our own are born. To state this with a more realistic example, take a tornado: sure, there is no reason why the tornado struck my house, but if we know enough about tornadoes we can say an awful lot about how they form, why they tend to touch down in certain areas more than in other areas, etc..

    An ideal situation would be that if one followed the regress back far enough, one would arrive at a single statement that is either self-referencing (i.e. it is its own reason), or could be no other way. That, I think, would be the dream of following this principle to its ultimate conclusion.

  • Daniel


    What exactly do you mean by a random process? I believe there are two main interpretations of randomness: one which we might call epistemic randomness, where the apparent randomness of an event stems from our ignorance of its causes, and ontological randomness, where the event actually cannot be predicted even assuming perfect knowledge of all relevant facts which might influence the event. It’s not clear whether or not the second exists in nature, and I believe that even if it were the case that some events were random in the strong sense, that it would not be provable that they were. (This would require perfect knowledge of the state of the universe, and somehow an ability to determine that the event could not have been predicted from this information. This seems impossible perhaps even in theory.)

    If in fact there were truly random events, then this would most certainly contradict the Principle of Sufficient Reason as described here, since a failure to be able to predict an event in terms of prior events would translate into an inability to explain it. (Consider that we can explain “why” an event has occured if and only if we can identify its causes, so the two ideas are really equivalent.)

  • Sean

    One of the problems with something like the PSR is that it’s very hard to define exactly what it means. I don’t have any strong ideas about what should really count as a “reason,” as I don’t think there’s any reason (ahem) to accept the PSR in the first place.

    Daniel, I wasn’t meaning to suggest that because this sunny philosophy had pernicious consequences, it must be incorrect. I was just saying that it could have pernicious consequences, despite being apparently sunny. That wouldn’t matter, if the PSR were correct, but I don’t think it is, for other reasons.

  • Daniel

    I think that to many people, this type of determinism that’s implied by a Principle of Sufficient Reason is seen as a bad thing. (After all, we don’t talk about Laplace’s Angel) For one, it’s often assumed to preclude the possibility of free will. I happen to think this is wrong, and that it actually is possible to have free will even in a completely deterministic universe. The idea is to simply note that the individual making the decision *is* whatever forces cause him to act in such and such a way. To illustrate, consider that if a billiard ball had a mind, and when it was struck by another ball felt a genuine compulsion to move in the appropriate direction, and then acted accordingly. We could meaningfully say that the billiard ball chose its behavior, since the mind of the billiard ball in a strange cognitive sense is “becoming” whatever law of nature causes it to move through perfect identification with it.

  • Neil B

    The PSR should not be confused with the idea that everything happens for a “reason” in the meaningfulness sense. It basically means, it is existentially peculiar for some features of reality to be blessed with being so, and others not. It has a counterpart in “symmetry” arguments. Of course random decay etc. already break PSR as far as causality for which moment in time, unless you believe in MW (see my comments in “What if Time Really Exists?”) Hence, Daniel above, were not not aware of quantum randomness or do you not agree with it – if not, why?

  • Daniel

    I’m not a physicist, so I don’t know. But I know there are enormous difficulties in claiming that any event is truly random in the strictest sense.

    Out of curiosity, how is it that physicists have demonstrated that there are events which are in fact completely unpredictable? It’s very easy to claim that, for instance, the flipping of a coin is completely unpredictable without knowing the presumed deterministic laws that govern it.

  • Otis

    So at what point would the scientific consensus conclude that certain “brute facts” cannot be understood and must therefore exist reasonlessly? When do you know the “ultimate rules”? What criteria should be applied to reach such a conclusion? Sean’s conjecture is naive and reveals the self-defeating nature of atheistic materialism. Since that philosophy cannot explain why the universe is knowable and understandable by humans, it yearns for “brute facts” that just “are,” or in Stephen Weinberg’s words, a universe that is absurd. Sean imagines a mythical unexplained Super Turtle holding up a tower of turtles that supports the universe.

    That super turtle representing “brute facts” will never be found by scientific investigation. Appealing to randomness and chance does not work since the ‘brute facts” must by definition be unique and not part of a random process. If they were, then where did the rules of that random process come from? You are stuck with an infinite regress. Atheistic materialism fails.

  • Neil B

    Otis, I think that ultimately you are right. It just doesn’t make sense for something as ultimately abstract as “existence” to be conditioned in terms of certain specific laws, and for the other “possible worlds” not to “exist.” So last (so far) but not least, here goes yet another excursion by Neil B into modal realism and ultimate reality!

    My critique of many universes with differing constants as an answer to
    1. fine-tuning for life, and
    2.the ultimate POSR problem of why this possible world is blessed to “‘exist” and others not: Where does it end? How many different kinds of reality are allowed to “exist”? What and why underlies the Über-laws” that determine the variation and scope of the other (more direct) “laws”, and what circumscribes the scope of “possible existence”? Modal realists make the cogent critique, that it doesn’t make sense at the highest level of abstraction for one “possible world” to “exist” and not other ones. (As I have said, it’s like the number 23 made into brass numerals while all the other ones remain abstractions – why “23” and not “15” or indeed all numbers reified, or none at all?)

    Indeed, they reject the very notion of “reification” as a genuine distinction at all. To them, every world in “Platonic reality” exists so as to avoid the violation of the grandest, existential principle of sufficient reason. Yes, that would mean cartoon type worlds and the adventures of Sherlock Holmes. (Look up on Wikipedia.)

    Well, that seems the perfect solution to fine-tuning (and so says Max Tegmark), since then every possible universe that can even be described at all exists/doesn’treallyexist and we are in a lucky one.

    But, I have a complaint which is also an argument for Goddidit: if every possible description is as real, then all the ones that involve irregular variations are as well. After all, “laws” are given after the fact if things are just “descriptions” with no inner virtus to “make” them so: if the forces follow 1/r^2, then we say pretentiously that they are “governed” by that law. But, it’s the other way around: that’s what things act like, so we are able to write that law. If they didn’t act like that, then we couldn’t.

    The objection might be, we wouldn’t have developed in a disorderly universe to start with. Sure, but Platonic descriptions include all the cases where things are orderly up to a point and then behave differently afterward (effectively, laws that change in all possible ways – which are part of Platonic reality too since we can say what would happen, however weird to us.)

    Since the range of variations is more than the orderly continuations: even if the world had incredibly remained orderly enough to nurture our development, we have a vanishingly small Bayesian expectation of continuing in a world that remains orderly. That is given that “laws” in modal realism would be after the fact generalizations, not enforcements in any sense. Since we are in an orderly universe, that looks like “Goddidit” since some overarching “management” has to step into the Platonic mess.


  • Neil B

    PS: Not only the problem of “laws” changing, but in MR we expect to find ourselves in a universe with ugly irregularities like slight variation in charge and mass of fundamental particles, etc.

  • Mark

    Personally, I’m not entirely comfortable with ethics (or morality) derived from a purely materialistic basis.

    I’m not really sure, either, what “enlightened” materialism would be. I’ve heard of “enlightened” self-interest as well, but it seems in both cases, the use of the word “enlightened” is more a dressing to make something sound better. It’s more akin to marketing jingle words.

    I wonder also what enlightenment might be, in materialism. I suppose you could say that something enlightened was sufficiently advanced in logical terms, and get away with it. But in materialism, could I be enlightened materialistically?

    It’s strange – something being enlightened has a metaphysical quality associated with it. Yet we’re applying it to materialism. What is enlightened here, when we talk about it?

    Smart materialism, and the abstraction of ethics that can grow out of it? Can a machine mind create an abstraction, like ethics, and have it be material?

    As for the notion of things just being as they are, with no reason… sure, I think you can have that. But it’s also a very lazy and dangerous cop-out, unless you’re really certain.

    Well, I just sound all negative here, don’t I? Sean, you know I love just about everything you do here. Well, at least you do now. I learn a lot, and I appreciate your sharing, greatly.

    This is a little bizarre, though. I’m curious, are you looking for some excuses for something? Some wriggle room somewhere?


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About Sean Carroll

Sean Carroll is a Senior Research Associate in the Department of Physics at the California Institute of Technology. His research interests include theoretical aspects of cosmology, field theory, and gravitation. His most recent book is The Particle at the End of the Universe, about the Large Hadron Collider and the search for the Higgs boson. Here are some of his favorite blog posts, home page, and email: carroll [at] .


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