Book Review: The Structure Of Scientific Revolutions

When I hear sci­en­tists talk about Thomas Kuhn, he sounds very rea­son­able. Scien­tists have the­o­ries that guide their work. Some­times they run into things their the­o­ries can’t ex­plain. Then some ge­nius de­vel­ops a new the­ory, and sci­en­tists are guided by that one. So the cy­cle re­peats, knowl­edge gained with ev­ery step.

When I hear philoso­phers talk about Thomas Kuhn, he sounds like a mad­man. There is no such thing as ground-level truth! Only the­ory! No ob­jec­tive sense-data! Only the­ory! No ba­sis for ac­cept­ing or re­ject­ing any the­ory over any other! Only the­ory! No sci­en­tists! Only the­o­ries, wear­ing lab coats and fake beards, hop­ing no­body will no­tice the cha­rade!

I de­cided to read Kuhn’s The Struc­ture Of Scien­tific Revolu­tions in or­der to un­der­stand this bet­ter. Hav­ing finished, I have come to a con­clu­sion: yup, I can see why this book causes so much con­fu­sion.

At first Kuhn’s the­sis ap­pears sim­ple, maybe even ob­vi­ous. I found my­self wor­ry­ing at times that he was knock­ing down a straw man, al­though of course we have to read the his­tory of philos­o­phy back­wards and re­mem­ber that Kuhn may already be in the wa­ter sup­ply, so to speak. He ar­gues against a sim­plis­tic view of sci­ence in which it is merely the grad­ual ac­cu­mu­la­tion of facts. So Aris­to­tle dis­cov­ered a few true facts, Gal­ileo added a few more on, then New­ton dis­cov­ered a few more, and now we have very many facts in­deed.

In this model, good sci­ence can­not dis­agree with other good sci­ence. You’re ei­ther wrong – as var­i­ous pseu­do­scien­tists and failed sci­en­tists have been through­out his­tory, posit­ing false ideas like “the brain is only there to cool the blood” or “the sun or­bits the earth”. Or you’re right, your ideas are en­shrined in the Sacristry Of Set­tled Science, and your facts join the ac­cu­mu­lated store that passes through the ages.

Sim­ple-ver­sion-of-Kuhn says this isn’t true. Science isn’t just facts. It’s paradigms – whole ways of look­ing at the world. Without a paradigm, sci­en­tists wouldn’t know what facts to gather, how to col­lect them, or what to do with them once they had them. With a paradigm, sci­en­tists gather and pro­cess facts in the ways the paradigm sug­gests (“nor­mal sci­ence”). Even­tu­ally, this pro­cess runs into a hitch – ap­par­ent con­tra­dic­tions, or things that don’t quite fit pre­dic­tions, or just a gi­ant ugly mess of epicy­cles. Some ge­nius de­vel­ops a new paradigm (“paradigm shift” or “sci­en­tific rev­olu­tion”). Then the pro­cess be­gins again. Facts can be ac­cu­mu­lated within a paradigm. And many of the facts ac­cu­mu­lated in one paradigm can sur­vive, with only slight trans­la­tion effort, into a new paradigm. But sci­en­tific progress is the story of one rel­a­tively-suc­cess­ful and gen­uinely-sci­en­tific effort giv­ing way to a differ­ent and con­tra­dic­tory rel­a­tively-suc­cess­ful and gen­uinely-sci­en­tific effort. It’s the story of sci­en­tists con­stantly toss­ing out one an­other’s work and be­gin­ning anew.

This gets awk­ward be­cause paradigms look a lot like facts. The atomic the­ory – the cur­rent paradigm in a lot of chem­istry – looks a lot like the fact “ev­ery­thing is made of atoms and molecules”. But this is only the ice­berg’s tip. Once you have atomic the­ory, chem­istry starts look­ing a lot differ­ent. Your first ques­tion when con­fronted with an un­known chem­i­cal is “what is the molec­u­lar struc­ture?” and you have pretty good ideas for how to figure this out. You are not par­tic­u­larly in­ter­ested in the sur­face ap­pear­ance of chem­i­cals, since you know that iron and silver can look al­ike but are to­tally differ­ent el­e­ments; you may be much more in­ter­ested in the weight ra­tio at which two chem­i­cals re­act (which might seem to the un­ini­ti­ated like a pretty ran­dom and silly thing to care about). If con­fronted with a gas, you might ask things like “which gas is it?” as op­posed to think­ing all gases are the same thing, or won­der­ing what it would even mean for two gases to be differ­ent. You can even think things like “this is a mix­ture of two differ­ent types of gas” with­out ag­o­niz­ing about how a perfectly uniform sub­stance can be a mix­ture of any­thing. If some­one asks you “How no­ble and close to God would say this chem­i­cal sam­ple is?” you can tell them that this is not re­ally a le­gi­t­i­mate chem­i­cal ques­tion, un­less you mean “no­ble” in the sense of the no­ble gases. If some­one tells you a cer­tain chem­i­cal is toxic be­cause tox­i­c­ity is a fun­da­men­tal prop­erty of its essence, you can tell them that no, it prob­a­bly has to do with some re­ac­tion it causes or fails to cause with chem­i­cals in the body. And if some­one tells you that a cer­tain chem­i­cal has changed into a differ­ent chem­i­cal be­cause it got colder, you can tell them that cold might have done some­thing to it, it might even have caused it to re­act with the air or some­thing, but chem­i­cals don’t change into other chem­i­cals in a fun­da­men­tal way just be­cause of the tem­per­a­ture. None of these things are ob­vi­ous. All of them are hard-won dis­cov­er­ies.

A field with­out paradigms looks like the STEM supremacist’s stereo­type of philos­o­phy. There are all kinds of differ­ent schools – Kan­ti­ans, Aris­totelians, Lock­eans – who all dis­agree with each other. There may be progress within a school – some Aris­totelian may come up with a re­ally cool new Aris­totelian way to look at bioethics, and all the other Aris­totelians may agree that it’s great – but the field as a whole does not progress. Peo­ple will talk past one an­other; the Aris­totelian can go on all day about the telos of the em­bryo, but the util­i­tar­ian is just go­ing to ask what the hell a telos is, why any­one would think em­bryos have one, and how many utils the em­bryo is bring­ing peo­ple. “De­bates” be­tween the Aris­totelian and the util­i­tar­ian may not be liter­ally im­pos­si­ble, but they are go­ing to have to go all the way to first prin­ci­ples, in a way that never works. Kuhn in­ter­est­ingly dis­misses these ar­eas as “the fields where peo­ple write books” – if you want to say any­thing, you might as well ad­dress it to a pop­u­lar au­di­ence for all the good other peo­ple’s pre-ex­ist­ing knowl­edge will do you, and you may have to spend hun­dreds of pages ex­plain­ing your en­tire sys­tem from the ground up. He throws all the so­cial sci­ences in this bin – you may read Freud, Sk­in­ner, and Beck in­stead of Aris­to­tle, Locke, and Kant, but it’s the same situ­a­tion.

A real sci­ence is one where ev­ery­one agrees on a sin­gle paradigm. New­to­ni­anism and Ein­stei­ni­anism are the same kind of things as Aris­totelianism and util­i­tar­i­anism; but in 1850, ev­ery­body be­lieved the former, and in 1950, the lat­ter.

I got con­fused by this – is Aris­totelian philos­o­phy a sci­ence? Would it be one if the Aris­totelians forced ev­ery non-Aris­totelian philoso­pher out of the academy, so that 100% of philoso­phers fell in line be­hind Aris­to­tle? I think Kuhn’s an­swer to this is that it’s tel­ling that Aris­totelians haven’t been able to do this (at least not lately); ei­ther Aris­to­tle’s the­o­ries are too weak, or philos­o­phy too in­tractable. But all physi­cists unite be­hind Ein­stein in a way that all philoso­phers can­not be­hind Aris­to­tle. Be­cause of this, all physi­cists mean more or less the same thing when they talk about “space” and “time”, and they can work to­gether on ex­plain­ing these con­cepts with­out con­stantly ar­gu­ing to each other about what they mean or whether they’re the right way to think about things at all (and a New­to­nian and Ein­stei­nian would not be able to do this with each other, any more than an Aris­totelian and util­i­tar­ian).

So how does sci­ence set­tle on a sin­gle paradigm when other fields can’t? Is this the part where we ad­mit it’s be­cause sci­ence has ob­jec­tive truth so you can just set­tle ques­tions with ex­per­i­ments?

This is very much not that part. Kuhn doesn’t think it’s any­where near that sim­ple, for a few rea­sons.

First, there is rarely a sin­gle ex­per­i­ment that one paradigm fails and an­other passes. Rather, there are dozens of ex­per­i­ments. One paradigm does bet­ter on some, the other paradigm does bet­ter on oth­ers, and ev­ery­one ar­gues over which ones should or shouldn’t count.

For ex­am­ple, one might try to test the Coper­ni­can vs. Ptole­maic wor­ld­views by ob­serv­ing the par­al­lax of the fixed stars over the course of a year. Coper­ni­cus pre­dicts it should be visi­ble; Ptolemy pre­dicts it shouldn’t be. It isn’t, which means ei­ther the Earth is fixed and un­mov­ing, or the stars are un­ut­ter­ably uni­mag­in­ably im­mensely im­pos­si­bly far away. No­body ex­pected the stars to be that far away, so ad­van­tage Ptolemy. Mean­while, the Coper­ni­cans posit far-off stars in or­der to save their paradigm. What looked like a test to se­lect one paradigm or the other has turned into a wedge push­ing the two paradigms even fur­ther apart.

What looks like a de­ci­sive vic­tory to one side may look like ran­dom noise to an­other. Did you know weird tech­nolog­i­cally ad­vanced ar­ti­facts are some­times found en­cased in rocks that our cur­rent un­der­stand­ing of ge­ol­ogy says are mil­lions of years old? Creation­ists have no trou­ble ex­plain­ing those – the rocks are much younger, and the ar­ti­facts were prob­a­bly planted by nephilim. Evolu­tion­ists have no idea how to ex­plain those, and de­fault to things like “the ar­ti­facts are hoaxes” or “the min­ers were re­ally care­less and a screw slipped from their pocket into the rock vein while they were min­ing”. I’m an evolu­tion­ist and I agree the ar­ti­facts are prob­a­bly hoaxes or mis­takes, even when there is no par­tic­u­lar ev­i­dence that they are. Mean­while, prob­a­bly cre­ation­ists say that some fos­sil or other in­com­pat­i­ble with cre­ation­ism is a hoax or a mis­take. But that means the “find some­thing pre­dicted by one paradigm but not the other, and then the failed the­ory comes crash­ing down” over­sim­plifi­ca­tion doesn’t work. Find some­thing pre­dicted by one paradigm but not the other, and of­ten the pro­po­nents of the dis­ad­van­taged paradigm can – and should – just shrug and say “what­ever”.

In 1870, flat-earther Sa­muel Row­botham performed a se­ries of ex­per­i­ments to show the Earth could not be a globe. In the most fa­mous, he placed sev­eral flags miles apart along a perfectly straight canal. Then he looked through a telescope and was able to see all of them in a row, even though the fur­thest should have been hid­den by the Earth’s cur­va­ture. Hav­ing done so, he con­cluded the Earth was flat, and the spher­i­cal-earth paradigm de­bunked. Alfred Wal­lace (more fa­mous for pre-empt­ing Dar­win on evolu­tion) took up the challenge, and showed that the bend­ing of light rays by at­mo­spheric re­frac­tion ex­plained Row­botham’s re­sult. It turns out that light rays curve down­ward at a rate equal to the cur­va­ture of the Earth’s sur­face! Luck­ily for Wal­lace, re­frac­tion was already a known phe­nomenon; if not, it would have been the same kind of wedge-be­tween-paradigms as the Coper­ni­cans hav­ing to change the dis­tance to the fixed stars.

It is all nice and well to say “Sure, it looks like your paradigm is right, but once we ad­just for this new idea about the dis­tance to the stars /​ the re­frac­tion of light, the ev­i­dence ac­tu­ally sup­ports my paradigm”. But the sup­port­ers of old paradigms can do that too! The Ptole­maics are rightly mocked for adding epicy­cle af­ter epicy­cle un­til their sys­tem gave the right re­sult. But to a hos­tile ob­server, posit­ing re­frac­tion effects that ex­actly coun­ter­bal­ance the cur­va­ture of the Earth sure looks like adding epicy­cles. At some point a new paradigm will win out, and its “epicy­cles” will look like perfectly rea­son­able ad­just­ments for re­al­ity’s sur­pris­ing amount of de­tail. And the old paradigm will lose, and its “epicy­cles” will look like ob­vi­ous kludges to cover up that it never re­ally worked. Be­fore that hap­pens…well, good luck.

Se­cond, two paradigms may not even ad­dress or care about the same ques­tions.

Let’s go back to util­i­tar­i­anism vs. Aris­totelianism. Many peo­ple as­so­ci­ate util­i­tar­i­anism with the trol­ley prob­lem, which is in­deed a good way to think about some of the is­sues in­volved. It might be tempt­ing for a util­i­tar­ian to think of Aris­totelian ethics as hav­ing some differ­ent an­swer to the trol­ley prob­lem. Maybe it does, I don’t know. But Aris­to­tle doesn’t talk about how he would solve what­ever the 4th-cen­tury BC equiv­a­lent of the trol­ley prob­lem was. He talks more about “what is the true mean­ing of jus­tice?” and stuff like that. While you can twist Aris­to­tle into hav­ing an opinion on trol­leys, he’s not re­ally op­ti­miz­ing for that. And while you can make util­i­tar­i­anism have some idea what the true mean­ing of jus­tice is, it’s not re­ally op­ti­mized for that ei­ther.

An Aris­totelian can say their paradigm is best, be­cause it does a great job ex­pli­cat­ing all the lit­tle types and sub­types of jus­tice. A util­i­tar­ian can say their paradigm is best, be­cause it does a great job tel­ling you how to act in var­i­ous con­trived moral dilem­mas.

It’s ac­tu­ally even worse than this. The clos­est thing I can think of to an an­cient Greek moral dilemma is the story of Anti­gone. Anti­gone’s un­cle de­clares that her traitorous dead brother may not be buried with the proper rites. Anti­gone is torn be­tween her duty to obey her un­cle, and her de­sire to honor her dead brother. Utili­tar­i­anism is…not re­ally de­signed for this sort of moral dilemma. Is ig­nor­ing her fam­ily squab­bles and try­ing to cure ty­phus an op­tion? No?

But then util­i­tar­i­anism’s prob­lems are deeper than just “comes to a differ­ent con­clu­sion than an­cient Greek morals would have”. The util­i­tar­ian’s job isn’t to change the an­cient Greek’s mind about the an­swer to a cer­tain prob­lem. It’s to con­vince him to stop car­ing about ba­si­cally all the prob­lems he cares about, and care about differ­ent prob­lems in­stead.

Third, two paradigms may dis­agree on what kind of an­swers are al­lowed, or what counts as solv­ing a prob­lem.

Kuhn talks about the 17th cen­tury “dor­mi­tive po­tency” dis­course. Aris­to­tle tended to ex­plain phe­nom­ena by ap­peal­ing to essences; trees grew be­cause it was “in their na­ture” to grow. Descartes gets a bad rap for in­vent­ing du­al­ism, but this is un­de­served – what he was re­ally do­ing was in­vent­ing the con­cept of “mat­ter” as we un­der­stand it, a what-you-see-is-what-you-get kind of stuff with no hid­den essences that re­sponds me­chan­i­cally to forces (and once you have this idea, you nat­u­rally need some other kind of stuff to be the mind). With Carte­sian mat­ter firmly in place, ev­ery­one made fun of Aris­to­tle for think­ing he had “solved” the “why do trees grow?” ques­tion by an­swer­ing “be­cause it is in their na­ture”, and this cli­maxed with the play­wright Moliere por­tray­ing a buf­foon­ish doc­tor who claimed to have dis­cov­ered how opium put peo­ple to sleep – it was be­cause it had a dor­mi­tive po­tency!

In Aris­to­tle’s view of mat­ter, say­ing “be­cause it’s their essence” suc­cess­fully an­swers ques­tions like “why do trees grow?”. The Carte­sian paradigm for­bade this kind of an­swer, and so many pre­vi­ously “solved” prob­lems like why trees grow be­came mys­te­ri­ous again – a step back­wards, sort of. For Descartes, you were only al­lowed to an­swer ques­tions if you could ex­plain how purely-me­chan­i­cal mat­ter smash­ing against other purely-me­chan­i­cal mat­ter in a billiard-ball-like way could pro­duce an effect; a more vir­tu­ous and Descartes-aware doc­tor ex­plained opium’s prop­er­ties by say­ing opium cor­pus­cles must have a sand­pa­per-like shape that smooths the neu­rons!

Then New­ton dis­cov­ered grav­ity and caused an up­roar. Grav­ity posits no cor­pus­cles jostling other cor­pus­cles. It sounds al­most Aris­totelian: “It is the na­ture of mat­ter to at­tract other mat­ter”. New­ton was de­nounced as try­ing to smug­gle oc­cultism into sci­ence. How much do you dis­count a the­ory for hav­ing oc­cult el­e­ments? If some con­cep­tion of quan­tum the­ory pre­dicts the data beau­tifully, but says mat­ter be­haves differ­ently de­pend­ing on whether some­one’s watch­ing it or not, is that okay? What if it says that a cer­tain elec­tron has a 50% chance of be­ing in a cer­tain place, full stop, and there is no con­ceiv­able ex­pla­na­tion for which of the two pos­si­bil­ities is re­al­ized, and you’re not even al­lowed to ask the ques­tion? What if my ex­pla­na­tion for dark mat­ter is “in­visi­ble grem­lins”? How do you figure out when you need to re­lax your as­sump­tions about what counts as sci­ence, ver­sus when some­body is just cheat­ing?

A less dra­matic ex­am­ple: Lavoisier’s the­ory of com­bus­tion boasts an abil­ity to ex­plain why some sub­stances gain weight when burned; they are ab­sorb­ing oxy­gen from the air. A brilli­ant ex­am­ple of an anomaly ex­plained, which proves the su­pe­ri­or­ity of com­bus­tion the­ory to other paradigms that can­not ac­count for the phe­nomenon? No – “things shouldn’t ran­domly gain weight” comes to us as a prin­ci­ple of the chem­i­cal rev­olu­tion of which Lavoisier was a part:

In the sev­en­teenth cen­tury, [an ex­pla­na­tion of weight gain] seemed un­nec­es­sary to most chemists. If chem­i­cal re­ac­tions could al­ter the vol­ume, color, and tex­ture of the in­gre­di­ents, why should they not al­ter weight as well? Weight was not always taken to be the mea­sure of quan­tity of mat­ter. Be­sides, weight-gain on roast­ing re­mained an iso­lated phe­nomenon. Most nat­u­ral bod­ies (eg wood) lose weight on roast­ing as the phlo­gis­ton the­ory was later to say they should.

In pre­vi­ous paradigms, weight gain wasn’t even an anomaly to be ex­plained. It was just a perfectly okay thing that might hap­pen. It’s only within the con­stel­la­tion of new meth­ods and rules we learned around Lavoisier’s time, that Lavoisier’s the­o­ries solved any­thing at all.

So how do sci­en­tists ever switch paradigms?

Kuhn thinks it’s kind of an ugly pro­cess. It starts with ex­as­per­a­tion; the old paradigm is clearly in­ad­e­quate. Progress is stag­nat­ing.

Aware­ness [of the in­ad­e­quacy of geo­cen­tric as­tron­omy] did come. By the thir­teenth cen­tury Alfonso X could pro­claim that if God had con­sulted him when cre­at­ing the uni­verse, he would have re­ceived good ad­vice. In the six­teenth cen­tury, Coper­ni­cus’ coworker, Domenico da No­vara, held that no sys­tem so cum­ber­some and in­ac­cu­rate as the Ptole­maic had be­come could pos­si­bly be true of na­ture. And Coper­ni­cus him­self wrote in the Pre­face to the De Revolu­tionibus that the as­tro­nom­i­cal tra­di­tion he in­her­ited had fi­nally cre­ated only a mon­ster.

Then some­one pro­poses a new paradigm. In its origi­nal form, it is woe­fully un­der­speci­fied, bad at match­ing re­al­ity, and only beats the old paradigm in a few test cases. For what­ever rea­son, a few peo­ple jump on board. Some­times the new paradigm is sim­ply more math­e­mat­i­cally el­e­gant, more beau­tiful. Other times it’s petty things, like a French­man in­vented the old paradigm and a Ger­man the new one, and you’re Ger­man. Some­times it’s just that there’s noth­ing bet­ter. Th­ese peo­ple grad­u­ally ex­pand the new paradigm to cover more and more cases. At some point, the new paradigm ex­plains things a lit­tle bet­ter than the old paradigm. Some of its pre­dic­tions are spook­ily good. The old paradigm is never con­clu­sively de­bunked. But the new paradigm now has enough ad­van­tages that more and more peo­ple hop on the band­wagon. Grad­u­ally the old paradigm be­comes a laugh­ing­stock, peo­ple for­get the con­text in which it ever made sense, and it is re­mem­bered only as a bunch of jokes about dor­mi­tive po­tency.

But now that it’s been adopted and ex­panded and reached the zenith of its power, this is the point at which we can ad­mit it’s ob­jec­tively bet­ter, right?

For a bet­ter treat­ment of this ques­tion than I can give, see Samz­dat’s Science Can­not Count To Red. But my im­pres­sion is that Kuhn is not re­ally will­ing to say this. I think he is of the “all mod­els are wrong, some are use­ful” camp, thinks of paradigms as mod­els, and would be will­ing to ad­mit a new paradigm may be more use­ful than an old one.

Can we sep­a­rate the fact around which a paradigm is based (like “the Earth or­bits the sun”) from the paradigm it­self (be­ing a col­lec­tion of defi­ni­tions of eg “planet” and “or­bit”, ways of think­ing, math­e­mat­i­cal meth­ods, and rules for what kind of sci­ence will and won’t be ac­cepted)? And then say the earth fac­tu­ally or­bits the sun, and the paradigm is just a use­ful tool that shouldn’t be judged ob­jec­tively? I think Kuhn’s an­swer is that facts can­not be paradigm-in­de­pen­dent. A me­dieval would not hear “the Earth or­bits the sun” and hear the same claim we hear (albeit, in his view wrong). He would, for ex­am­ple, in­ter­pret it to mean the Earth was set in a slowly-turn­ing crys­tal sphere with the sun at its cen­ter. Then he might ask – where does the sphere in­ter­sect the Earth? How come we can’t see it? Is Marco Polo go­ing to try to travel to China and then hit a huge in­visi­ble wall halfway across the Hi­malayas? And what about grav­ity? My un­der­stand­ing is the Ptole­maics didn’t be­lieve in grav­ity as we un­der­stand it at all. They be­lieved ob­jects had a nat­u­ral ten­dency to seek the cen­ter of the uni­verse. So if the sun is more cen­tral, why isn’t ev­ery­thing fal­ling into the sun? To a me­dieval the state­ment “the Earth or­bits the sun” has a bunch of com­mon-sense dis­proofs ev­ery­where you look. It’s only when at­tached to the rest of the Coper­ni­can paradigm that it starts to make sense.

This im­presses me less than it im­presses Kuhn. I would say “if you have many false be­liefs, then true state­ments may be con­fus­ing in that they seem to im­ply false state­ments – but true state­ments are still ob­jec­tively true”. Per­haps I am mi­s­un­der­stand­ing Kuhn’s ar­gu­ment here; the above is an amalgam of var­i­ous things and not some­thing Kuhn says out­right in the book. But what­ever his ar­gu­ment, Kuhn is not re­ally will­ing to say that there are definite paradigm-in­de­pen­dent ob­jec­tive facts, at least not with­out a lot of caveats.

So where is the point at which we ad­mit some things are ob­jec­tively true and that’s what this whole en­ter­prise rests on?

Kuhn only barely touches on this, in the last page of the book:

Any­one who has fol­lowed the ar­gu­ment this far will nev­er­the­less feel the need to ask why the evolu­tion­ary pro­cess should work. What must na­ture, in­clud­ing man, be like in or­der that sci­ence be pos­si­ble at all? Why should sci­en­tific com­mu­ni­ties be able to reach a firm con­sen­sus unattain­able in other fields? Why should con­sen­sus en­dure across one paradigm change af­ter an­other? And why should paradigm change in­vari­ably pro­duce an in­stru­ment more perfect in any sense than those known be­fore? From one point of view those ques­tions, ex­cept­ing the first, have already been an­swered. But from an­other they are as open as they were when this es­say be­gan. It is not only the sci­en­tific com­mu­nity that must be spe­cial. The world of which that com­mu­nity is a part must also pos­sess quite spe­cial char­ac­ter­is­tics, and we are no closer than we were at the start to know­ing what these must be. That prob­lem— What must the world be like in or­der that man may know it?— was not, how­ever, cre­ated by this es­say. On the con­trary, it is as old as sci­ence it­self, and it re­mains unan­swered. But it need not be an­swered in this place.

At this point I lose pa­tience. Kuhn is no longer be­ing thought-pro­vok­ing, he’s be­ing dis­in­gen­u­ous. IT’S BECAUSE THERE’S AN OBJECTIVE REALITY, TOM. YOU DON’T HAVE TO BE SO COY ABOUT IT. “OHHHHH, WHAT COULD POSSIBLY EXPLAIN WHY SCIENCE BEHAVES THE WAY IT WOULD IF OBJECTIVE REALITY EXISTS, NOBODY WILL EVER KNOW, LET’S JUST NEVER ANSWER IT”. Get a life.

Hon­estly this de­creases my trust in some of what’s come be­fore. Maybe he wrote all those sec­tions about in­com­men­su­rable paradigms be­cause paradigms re­ally are that in­com­men­su­rable. Or maybe it’s be­cause he thinks he’s play­ing some kind of ridicu­lous game where the first per­son to ad­mit the ex­is­tence of ob­jec­tive re­al­ity loses.

II.

A lot of the ex­am­ples above are mine, not Kuhn’s. Some of them even come from philos­o­phy or other non­scien­tific fields. Shouldn’t I have used the book’s own ex­am­ples?

Yes. But one of my big com­plaints about this book is that, for a pur­ported de­scrip­tion of How Science Every­where Is Always Prac­ticed, it re­ally just gives five ex­am­ples. Ptolemy/​Coper­ni­cus on as­tron­omy. Alchemy/​Dal­ton on chem­istry. Phlo­gis­ton/​Lavoisier on com­bus­tion. Aris­to­tle/​Gal­ileo/​New­ton/​Ein­stein on mo­tion. And ???/​Fran­klin/​Coulomb on elec­tric­ity.

It doesn’t ex­plain any of the ex­am­ples. If you don’t already know what Coulomb’s con­tri­bu­tion to elec­tric­ity is and what pre­vi­ous ideas he over­turned, you’re out of luck. And don’t try look­ing it up in a book ei­ther. Kuhn says that all the books have been writ­ten by peo­ple so en­grossed in the cur­rent paradigm that they un­con­sciously jam past sci­en­tists into it, re­mov­ing all ev­i­dence of paradigm shift. This made parts of the book a lit­tle be­yond my level, since my knowl­edge of Coulomb be­gins and ends with “one amp per sec­ond”.

Even say­ing Kuhn has five ex­am­ples is giv­ing him too much credit. He usu­ally brings in one of his five per point he’s try­ing to make, mean­ing that you never get a re­ally full view of how any of the five ex­am­ples ex­actly fit into his sys­tem.

And all five ex­am­ples are from physics. Kuhn says at the be­gin­ning that he wished he had time to talk about how his sys­tem fits biol­ogy, but he doesn’t. He’s un­sure whether any of the so­cial sci­ences are sci­ences at all, and noth­ing else even gets men­tioned. This means we have to figure out how Kuhn’s the­ory fits ev­ery­thing from scat­ter­shot looks at the his­tory of elec­tric­ity and as­tron­omy and a few other things. This is pretty hard. For ex­am­ple, con­sider three sci­en­tific pa­pers I’ve looked at on this blog re­cently:

Cipri­ani, Ioan­ni­dis, et al perform a meta-anal­y­sis of an­tide­pres­sant effect sizes and find that al­though al­most all of them seem to work, amitriptyline works best.

Ce­bal­los, Ehrlich, et al calcu­late whether more species have be­come ex­tinct re­cently than would be ex­pected based on his­tor­i­cal back­ground rates; af­ter find­ing al­most 500 ex­tinc­tions since 1900, they con­clude they definitely have.

Ter­rell et al ex­am­ine con­tri­bu­tions to open source pro­jects and find that men are more likely to be ac­cepted than women when ad­justed for some mea­sure of com­pe­tence they be­lieve is ap­pro­pri­ate, sug­gest­ing a gen­der bias.

What paradigm is each of these work­ing from?

You could ar­gue that the an­tide­pres­sant study is work­ing off of the “biolog­i­cal psy­chi­a­try” paradigm, a ven­er­a­ble col­lec­tion of as­sump­tions that can be prof­itably con­trasted with other paradigms like psy­cho­anal­y­sis. But couldn’t a Hip­po­cratic four-hu­mors physi­cian of a thou­sand years ago done the same thing? A meta-anal­y­sis of the effect sizes of var­i­ous kinds of leeches for de­pres­sion? Sure, leeches are differ­ent from an­tide­pres­sants, but it doesn’t look like the be­lief in biolog­i­cal psy­chi­a­try is af­fect­ing any­thing about the re­search other than the topic. And al­though the topic is cer­tainly im­por­tant, Kuhn led me to ex­pect some­thing more profound than that. Maybe the paradigm is ev­i­dence-based-medicine it­self, the prac­tice of do­ing RCTs and meta-analy­ses on things? I think this is a stronger case, but a paradigm com­pletely di­vorced from the con­tent of what it’s study­ing is ex­actly the sort of weird thing that makes me wish Kuhn had in­cluded more than five ex­am­ples.

As for the ex­tinc­tion pa­per, surely it can be at­tributed to some chain of thought start­ing with Cu­vier’s catas­trophism, pass­ing through Lyell, and con­tin­u­ing on to the cur­rent day, based on the idea that the world has changed dra­mat­i­cally over its his­tory and new species can arise and old ones dis­ap­pear. But is that “the” paradigm of biol­ogy, or ecol­ogy, or what­ever field Ce­bal­los and Lyell are work­ing in? Doesn’t it also de­pend on the idea of species, a differ­ent paradigm start­ing with Lin­naeus and de­vel­oped by zo­ol­o­gists over the en­su­ing cen­turies? It look like it dips into a bunch of differ­ent paradigms, but is not wholly within any.

And the open source pa­per? Is “fem­i­nism” a paradigm? But surely this is no differ­ent than what would be done to in­ves­ti­gate racist bi­ases in open source. Or some right-winger look­ing for anti-Chris­tian bi­ases in open source. Is the paradigm just “look­ing for bi­ases in things?”

What about my fa­vorite triv­ial ex­am­ple, look­ing both ways when you cross the street so you don’t get hit by a bus? Is it based on a paradigm of mo­tor­ized trans­porta­tion? Does it use as­sump­tions like “buses ex­ist” and “roads are there to be crossed”? Was there a paradigm shift be­tween the bad old days of look­ing one way be­fore cross­ing, and the ex­cit­ing new de­vel­op­ment of look­ing both ways be­fore cross­ing? Is this re­ally that much more of a stretch than call­ing look­ing for bi­ases in things a paradigm?

Out­side the five ex­am­ples Kuhn gives from the phys­i­cal sci­ences, iden­ti­fy­ing paradigms seems pretty hard – or maybe too easy. Is it all frac­tal? Are there over­ar­ch­ing paradigms like atomic the­ory, and then lower-level paradigms like or­ganic chem­istry, and then tiny sub­sub­paradigms like “how we deal with this one or­ganic com­pound”? Does ev­ery sci­en­tific ex­per­i­ment use lots of differ­ent paradigms from differ­ent tra­di­tions and differ­ent lev­els? This is the kind of thing I wish Kuhn’s book an­swered in­stead of just talk­ing about Coulumb and Coper­ni­cus over and over again.

III.

In con­clu­sion, all of this is about pre­dic­tive cod­ing.

It’s the same thing. Per­cep­tion get­ting guided equally by top-down ex­pec­ta­tions and bot­tom-up ev­i­dence. Oh, I know what you’re think­ing. “There goes Scott again, see­ing pre­dic­tive cod­ing in ev­ery­thing”. And yes. But also, Kuhn does ev­ery­thing short of come out and say “When you guys get around to in­vent­ing pre­dic­tive cod­ing, make sure to no­tice that’s what I was get­ting at this whole time.”

Don’t be­lieve me? From the chap­ter Ano­maly And The Emer­gence Of Scien­tific Dis­cov­ery (my em­pha­sis, and for “anomaly”, read “sur­prisal”):

The char­ac­ter­is­tics com­mon to the three ex­am­ples above are char­ac­ter­is­tic of all dis­cov­er­ies from which new sorts of phe­nom­ena emerge. Those char­ac­ter­is­tics in­clude: the pre­vi­ous aware­ness of anomaly, the grad­ual and si­mul­ta­neous emer­gence of both ob­ser­va­tional and con­cep­tual recog­ni­tion, and the con­se­quent change of paradigm cat­e­gories and pro­ce­dures of­ten ac­com­panied by re­sis­tance.

There is even ev­i­dence that these same char­ac­ter­is­tics are built into the na­ture of the per­cep­tual pro­cess it­self. In a psy­cholog­i­cal ex­per­i­ment that de­serves to be far bet­ter known out­side the trade, Bruner and Post­man asked ex­per­i­men­tal sub­jects to iden­tify on short and con­trol­led ex­po­sure a se­ries of play­ing cards. Many of the cards were nor­mal, but some were made anoma­lous, e.g., a red six of spades and a black four of hearts. Each ex­per­i­men­tal run was con­sti­tuted by the dis­play of a sin­gle card to a sin­gle sub­ject in a se­ries of grad­u­ally in­creased ex­po­sures. After each ex­po­sure the sub­ject was asked what he had seen, and the run was ter­mi­nated by two suc­ces­sive cor­rect iden­ti­fi­ca­tions.

Even on the short­est ex­po­sures many sub­jects iden­ti­fied most of the cards, and af­ter a small in­crease all the sub­jects iden­ti­fied them all. For the nor­mal cards these iden­ti­fi­ca­tions were usu­ally cor­rect, but the anoma­lous cards were al­most always iden­ti­fied, with­out ap­par­ent hes­i­ta­tion or puz­zle­ment, as nor­mal. The black four of hearts might, for ex­am­ple, be iden­ti­fied as the four of ei­ther spades or hearts. Without any aware­ness of trou­ble, it was im­me­di­ately fit­ted to one of the con­cep­tual cat­e­gories pre­pared by prior ex­pe­rience. One would not even like to say that the sub­jects had seen some­thing differ­ent from what they iden­ti­fied. With a fur­ther in­crease of ex­po­sure to the anoma­lous cards, sub­jects did be­gin to hes­i­tate and to dis­play aware­ness of anomaly. Ex­posed, for ex­am­ple, to the red six of spades, some would say: That’s the six of spades, but there’s some­thing wrong with it— the black has a red bor­der. Fur­ther in­crease of ex­po­sure re­sulted in still more hes­i­ta­tion and con­fu­sion un­til fi­nally, and some­times quite sud­denly, most sub­jects would pro­duce the cor­rect iden­ti­fi­ca­tion with­out hes­i­ta­tion. More­over, af­ter do­ing this with two or three of the anoma­lous cards, they would have lit­tle fur­ther difficulty with the oth­ers. A few sub­jects, how­ever, were never able to make the req­ui­site ad­just­ment of their cat­e­gories. Even at forty times the av­er­age ex­po­sure re­quired to rec­og­nize nor­mal cards for what they were, more than 10 per cent of the anoma­lous cards were not cor­rectly iden­ti­fied. And the sub­jects who then failed of­ten ex­pe­rienced acute per­sonal dis­tress. One of them ex­claimed: “I can’t make the suit out, what­ever it is. It didn’t even look like a card that time. I don’t know what color it is now or whether it’s a spade or a heart. I’m not even sure now what a spade looks like. My God!” In the next sec­tion we shall oc­ca­sion­ally see sci­en­tists be­hav­ing this way too.

Either as a metaphor or be­cause it re­flects the na­ture of the mind, that psy­cholog­i­cal ex­per­i­ment pro­vides a won­der­fully sim­ple and co­gent schema for the pro­cess of sci­en­tific dis­cov­ery.

And from Revolu­tions As Changes Of World-View:

Sur­vey­ing the rich ex­per­i­men­tal liter­a­ture from which these ex­am­ples are drawn makes one sus­pect that some­thing like a paradigm is pre­req­ui­site to per­cep­tion it­self. What a man sees de­pends both upon what he looks at and also upon what his pre­vi­ous vi­sual-con­cep­tual ex­pe­rience has taught him to see. In the ab­sence of such train­ing there can only be, in William James’s phrase, “a bloomin’ buzzin’ con­fu­sion.” In re­cent years sev­eral of those con­cerned with the his­tory of sci­ence have found the sorts of ex­per­i­ments de­scribed above im­mensely sug­ges­tive.

If you can read those para­graphs and hon­estly still think I’m just just ir­ra­tionally read­ing pre­dic­tive cod­ing into a perfectly in­no­cent book, I have noth­ing to say to you.

I think this is my best an­swer to the whole “is Kuhn deny­ing an ob­jec­tive re­al­ity” is­sue. If Kuhn and the pre­dic­tive cod­ing peo­ple are grasp­ing at the same thing from differ­ent an­gles, then both shed some light on each other. I think I un­der­stand the way that pre­dic­tive cod­ing bal­ances the im­por­tance of pre-ex­ist­ing struc­tures and cat­e­gories with a pre­served be­lief in ob­jec­tivity. If Kuhn is try­ing to use some­thing like the pre­dic­tive cod­ing model of the brain pro­cess­ing in­for­ma­tion to un­der­stand the way the sci­en­tific com­mu­nity as a whole pro­cesses it, then maybe we can im­port the same bal­ance and not worry about it as much.