This is very interesting indeed! I'm not sure how much we can get to bias, or whether it's about what the argument is trying to say. Is he asserting that those 8 are the (only) relevant things that could make agriculture more likely? It's awhile since I read it, but I saw it more as saying that those 8 are the reason why historically it was the Fertile Crescent. Not that it would always be those things on any remotely similar world, or even necessarily that it would always be there if you re-ran history. In fact, as you say, he seems to mostly be arguing why it's plausibly NOT the 'people from the Fertile Crescent are superior' argument. Or more strongly, why the geographical case is more compelling than the gene-based one.
Say there's a ninth category (I dunno, 'distance from steppes which tend to be full of dangerous nomads') which Fertile Crescent scores badly on, and which makes it 'less likely' to develop agriculture. If what we're trying to explain is why Fertile Crescent succeeded, we don't necessarily focus on that. If we wanted to give a complete explanation, we might do, but it's not necessary. Similarly, if we wanted to say 'why did Sparta beat Athens' we could point to the army, and if we wanted to ask 'why did Athens beat Sparta', we'd point to the navy (or whatever). The fact we can go either way shows that this explanation isn't strong enough to be predictive, but it gives a compelling alternative to 'innate cultural/genetic superiority'
Thanks, good comment. Yes Diamond wants to give a compelling alternative to 'innate cultural/genetic superiority'. When he is doing that, it is, however, his responsibility to discuss evidence that tells against his theory too, such as geographical factors decreasing the chance that the agricultural revolution would occur in the Fertile Crescent. What he should have said is that yes, there are such factors, but that the Fertile Crescent still had, all things considered, geographical advantages.
It is true that when explaining "Why did Athens beat Sparta?" we don't focus on Sparta's advantages over Athens. I am however to a certain extent questioning that practice which I think comes from our System 1-driven urge for one-sided stories. It depends a bit on context, but normally we should be most interested in learning about the factors that had most causal impact on the event in question. It should be more valuable to learn of a factor that played strongly to Sparta's advantage than one that played weakly to Athens' advantage.
In a way what we want to explain is not "Why did Athens beat Sparta?" but rather "Why did Athens beat Sparta with amount x?" since we know the latter. Now with the latter formulation, it becomes clear that unless x is very large (whatever that means) some of the factors used to answer this question should play to Sparta's advantage.
I don't think I really disagree with any of this! My point was that, as things stand, this isn't a case of individuals having confirmation bias, but of the system of how we as a society/culture/academy tend to approach the concept of 'explaining something'.
As far as I can see, your approach ends up not being focused on actually explaining a specific thing at all, but rather identifying all the stuff going on in a certain area under certain categories. Reminds me a bit of http://lesswrong.com/lw/h1/the_scales_of_justice_the_notebook_of_rationality/ in that regard.
If we know loads about a certain thing then this might also clearly point to why it was 'inevitable' that what happened did. But before then (and I doubt we know that much about Athens/Sparta or about the rise of agriculture), it mainly functions to turn 'explanations' into 'enumerations of relevant facts'. This is good in some ways because it stops people thinking issues have been resolved - I can imagine lots of people take Diamond's analysis to 'disprove' other accounts of the rise of agriculture, for instance. The downside is that given our psychology as it is, I suspect we think about things better when people are creating hypotheses and arguing for/against them rather than contesting the detail of a list of possible factors with no clear conclusion.
Thanks, this is useful. We may compare with policy debates. The reason any individual's arguments in a policy debate might either be that they are biased or that they are intentionally only putting forward arguments that support their position for strategic reasons. It could be argued that there is a convention to the effect that this is allowable, particularly in e.g. political debates.
Similarly, the reason why a multiple factor explanation is one-sided might either be bias or that the author intentionally leaves out mechanism playing in the other direction for strategic reasons. (Thanks for reminding me of this!) In your opinion, there is a convention to the effect that this is allowable. I'm a bit more unsure about this, but it is always hard to establish what the implicit conventions regulating various sort of behaviour are, particularly complex and abstract sorts of behaviour as this. Also, if there is such a convention, it could be argued that it arose precisely because people are normally confirmation biased, which has led them to regularly give these sorts of one-sided explanations, which in turn made this a convention.
I do not know whether Diamond is biased or if he is doing this intentionally, but would guess at the former. I think, firstly, that he should be much clearer over what he is doing. If he only wants to list mechanisms playing in the one direction, they should explicitly say so.
But I also think it is unreasonable to only list mechanisms playing in the one direction, especially when there are stronger mechanisms playing in the other direction. Learning about those other mechanisms is clearly very useful for the reader wanting to get a grasp of why the agricultural revolution first occurred in the Fertile Crescent.
Our intuitions are a bit muddled here, I think, because it is so hard to obtain reliable knowledge concerning why the agricultural revolution occurred in the Fertile Crescent. Let us therefore instead look at an example where we do have somewhat better knowledge: climate change. When explaining why the climate has got hotter, it would be unreasonable, at least in a serious scientific context, not to mention mechanisms that have forced the climate to grow colder than it otherwise would have, such as global dimming. Indeed, the Wikipedia article on global warming does mention global dimming. Mentioning this factor is very important not the least because it tells us that the mechanisms warming the Earth are stronger than we would have had reason to believe if there hadn't been any counteracting factors.
One important upshot of this is that the notion of an "explanation" can be a bit misleading here. We need to be very clear over what it is that we want to explain. It is true that people sometimes do understand "Why did Athens beat Sparta?" as a call to list all factors that played to Athens advantage, and none that played to Sparta's advantage. But under normal circumstances, that is not what we should be interested in.
The downside is that given our psychology as it is, I suspect we think about things better when people are creating hypotheses and arguing for/against them rather than contesting the detail of a list of possible factors with no clear conclusion.
I think that you could come with a clear conclusion even if you mention counteracting forces. Indeed, I think that Diamond's theory is basically right and that he could show that these counteracting forces were clearly too weak to overcome the Fertile Crescent's geographical advantages (though this is just a hunch - I'm not an expert on that issue and only interested in this as an example of the methodological problem under discussion).
Cheers for the thoughtful response! I think your global warming argument is subtly different: people don't want to just explain why temparatures rose at a certain point in the past (which would be the equivalent of Diamond's argument). They want to understand whether we should expect temparatures to rise in the future.
The question here is not 'Why did Athens beat Sparta', but closer to 'as Corinthians watching the arms race, should we expect Athens or Sparta to win next time'. In this case, we definitely want to know both sides, even if Athens has won all of the conflicts we've seen: for instance if all the other conflicts they won with ships and this is a landlocked struggle for some reason, that would change our conclusions.
What stands out here is that this sort of balanced account is what you want as soon as you expect your beliefs to 'pay rent'. A historical explanation which simply explains what series of events led to a certain event isn't necessarily particularly useful, even if it's true.
So for instance, a historian might seek to show that the First World War was caused by the shooting of Franz Ferdinand or that it inevitably followed from the alliance system of the early twentieth century. These explanations wouldn't necessarily ask 'what other things might cause world wars?' or 'what things were going on that might have stopped this world war?' unless they were directly relevant. And because of that, the primary purpose is to establish once particular incident of causation, not to draw general lessons that shooting archdukes is a Bad Idea or that all world wars are caused by the fallacious belief that having two huge blocs would deter each other..
On the other hand, historians might argue that more general economic/social laws apply through history: that slave cultures are at a significant advantage/disadvantage in war, that wars tend to lead to greater/lesser power for the previously downtrodden, that feudal systems tend to turn into democratic systems or whatever. For those cases the aspiration is to have some predictive power, and so both sides are needed.
That is another interesting idea. You're right that we're more interested in prediction and in general laws in the climate change case. Generally, I am all for identifying general historical/social laws and don't think that we should just describe particular events.
But even someone who wants to describe particular events should, in my view, include both pro- and contra-factors. This is clearest if we suppose that the Fertile Crescent had an extremely large geographical disadvantage, say re-occuring draughts which would kill most farmers but which hunter-gatherers would survive since they are more mobile. Say that this was also generally known among readers of Diamond's book. In that case, his explanation wouldn't feel sufficient if he hadn't mentioned this fact, and shown that the counteracting geographical factors nevertheles are stronger, and I'm sure that he would have done so.
As a matter of fact, there is no such very strong and well-known factor. Hence Diamond can get away with not including any contra-factor. However, the fact that these factors are weaker and not as well-known as the imagined draught factor does not mean that the same logic doesn't apply. The fact that they aren't well-known seems to me to be irrelevant: then it's Diamond's duty to tell us about them. The fact that they are weaker makes the omission a bit less glaring, but they should still be included if they are stronger than some of the pro-mechanisms that Diamond does mention.
I guess I have the intuition that it is not very honest to fail to present contra-mechanisms that are stronger than some of the pro-mechanisms. But you don't share that intuition?
I think my intuition depends on the context, to be honest: and I don't have Diamond's book to hand (don't think I own it, though I read it a few years ago).
I think it's clear that the briefest possible explanation of why a specific event happened is the key positive causes. Then you have the option of including two other sorts of things
Say you're explaining why a country elected a particular political party. You would most naturally talk about the positives: 'polls showed they were trusted on issues X and Y'. You'd mostly talk about overcoming negatives where there was a important change in that area - people previously didn't like them because they associated them with policy Z, but the new leader convinced many voters that this was a thing of the past'. It wouldn't be as relevant in a short summary to say 'they probably lost some votes because of issues A and B' or 'while another party in a different country is trusted on the same issues, they lost an election six months later - the difference is due to C and D'
There's a difference here with policy debates, because they are saying what we should do, rather than trying to trace the line of what led to a particular thing that happened. Personally, I'd be much happier giving a one-sided account that said 'political position X is widely supported because of the following factors' than a one-sided account that said 'political position X SHOULD BE widely supported because of the following factors', even if the following detail was identical.
A lot of this might be quite parochial and based on various academic/journalistic/professional traditions, though. I'm trying to wrap my head round the underlying point about facts causing their evidence but this not applying to policy debates/moral positions/multiple factor explanations. I think I basically agree that multiple factor explanations are analagous to policy debates in this regard, but I'm trying to unpack some examples on the moral front to see if I agree there...
That's interesting. A colleague of mine raised a similar issue, namely that in a popular science book you don't necessarily want to complicate things by including countervailing factors. In your terms, you settle for the briefest possible explanation. Diamond's and Pinker's books are directed both towards the scientific community and towards the general public, so it's a bit of a tricky case, but since they are such high-profile scientists and since their books have been so influential, I think it is legitimate to criticize them on this score.
A perhaps more glaring example is this. Man City won Premier League 2012 on goal difference thanks to a 94 minute goal which put them ahead of Man Utd. Afterwards, a Swedish pundit was asked to explain why Man City won the Premier League. This is in a sense absurd, since it's clear that if a 38-matches league is settled on overtime of the last game, there is very little that distinguishes the two team in terms of quality. But the pundit's reaction was also absurd: he went on to provide 4-5 reasons for why Man City was better than Man Utd, to which my reaction was, well, if they're better on so many scores, then why didn't they finish like 20 points ahead? The "briefest possible explanation" defense doesn't work here, since it would have been easier just to give one reason, and more adequate given the small difference between the teams, than 4-5. Instead, I believe that he did so because of a deeply felt urge to tell a "story". I think that the halo effect is at play here. Our system 1 wants to tell one-sided stories where the winning team had all the advantages and the losing team was worse across the board.
Now Diamond and Pinker are obviously better than football pundits, but I don't think that the examples are fundamentally different. They, too, are most likely to some degree engaging in story-telling.
Sorry for following you around so much (I just read this article since you linked to it in our other discussion)
There are two main points, both of which have largely been said or touched on already in your discussion here:
1) When discussing an event or something "playing out," we are talking about a cause and effect. Despite the fact that many things in life have many factors, there are always positive causes for things, which may or may not have counteracting factors. When we want to describe an effect of interest, then the simplest way to do it is to list the cause(s).
2) There are several factors (that I've thought of off the top of my head) that play into what kinds of points you provide when you are presenting a cause/effect relationship:
The first (which DavidAgain mentioned somewhat already) is whether you are trying to describe something that has happened or something that will happen. When we don't know what the outcome of something will be, we must exhaustively weigh all of the factors that we know of and their possible interactions in order to come to the best conclusion about the result. (Really there are two variations on this: what action should be taken vs. what will happen given the current state of the world, but the concept holds in each). If, however, something has already happened, it is reasonable to focus on the causes, A) because we know that they ended up "winning" and B) because there may or may not be negating factors involved in the first place.
If I say something along the lines of "I went swimming today because I was hot," it is not dishonest/biased to refrain from mentioning the fact that I weighed this course of action against several reasons not to do so - the important, primary causation was relayed in the statement and satisfies most people to the extent that they care about the factors involved.
Another factor that might be relevant is how contentious the subject is; even if you are debating something in the past, such as why X happened (or offering a proposal for why X happened), if the conclusion to be drawn is not readily agreed upon then it is prudent to first make sure that all of the relevant facts are presented. On the other hand, if you're trying to teach/explain why something happened in a non-contentious atmosphere, then it may be reasonable to omit facts that are unimportant to maintain coherency and avoid getting bogged down in clutter that doesn't matter to the overarching point. Which category Diamond's book falls under is a bit unclear, but I still am not convinced that it was biased to provide causes without enumerating all of the pros/cons, given that you trust him to the extent that he is telling the truth when we says that the Fertile Crescent was a highly, if not the most advantageous locations for the start of agriculture.
I am on the fence as to whether or not Jared Diamond was slightly biased in this case, but I think it depends on whether you look at his book from the perspective of a comprehensive argument/claim or a proposition of a different mechanism behind how things ended up the way they did which may or may not account for all of history in its complex entirety.
Anyway, I think trying to infer bias based on the presence of pros/cons is a difficult subject. I wouldn't go claiming someone is biased towards something for only presenting a positive message necessarily, even though this is often the case. Even in the example with the teams coming very close to a tie, the response to "why did they win" may have been correct, in that they had all of those factors in their favor and that those were enough to win (barely). I agree that in this case the guy was biased, but on the other hand they didn't ask him "what factors were involved and why did they favor Man City (somewhat)?"
That's about all I'll say for one response - I have a bad tendency of rambling on when I've already made the points that I really wanted to make.
(by the way DavidAgain I loved the way you said the things I was thinking with each consecutive response - I was vicariously participating in the discussion through your comments!)
Firstly, giving reasons for your own choices is something a bit different from explaining events over which you had no control. I'd rather concentrate on the latter cases.
On the other hand, if you're trying to teach/explain why something happened in a non-contentious atmosphere, then it may be reasonable to omit facts that are unimportant to maintain coherency and avoid getting bogged down in clutter that doesn't matter to the overarching point.
Sure. I do think that Diamond should have provided pros and cons (and Pinker even more so). However, this discussion has been very useful to me in that I realize that others have different intuitions.
Suppose that there is a convention which says that it's ok to omit countervailing factors (which I'm not sure there is). In that case, Diamond and Pinker are at least to some extent forgiven - they are merely following a convention. However, then I'd say that the convention should be abandoned, because I, as a reader, do want to get the full picture, and not a cherry-picked selection of factors.
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Even in the example with the teams coming very close to a tie, the response to "why did they win" may have been correct, in that they had all of those factors in their favor and that those were enough to win (barely). I agree that in this case the guy was biased, but on the other hand they didn't ask him "what factors were involved and why did they favor Man City (somewhat)?"
Sure. The question kind of suggests an answer along these lines - which support the notion that there is a convention according to which we're expected only to give pro-reasons. But in this case, this is clearly absurd. Why would I want to hear about Man City's fifth best characteristic (relative to Man U) over Man U's best characteristic (relative to Man C)?
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Generally, I also think that people have a bias against admitting bias, especially in themselves, but also in others. Philosophers and others have defended the hypothesis that humans are basically rational to absurdity, to my mind, despite the overwhelming evidence to the contrary. (See this excellent post on this, for instance. But the same goes not only for the notion of whether humans are rational in general, but also for whether any particular thought-process was rational or biased. I think that, given what we know about the ubiquity of human biases (as shown in experiments), we should be very open to the possibility that even great books like Diamond's and Pinker's are filled with inferences which are not rational but rather due to biases. This goes particularly for inferences and reasonings in messy and inexact fields. I would be very surprised if someone was able to escape to form very general historical theories such as these without falling prey to at least some biases on a major scale.
That's about all I'll say for one response - I have a bad tendency of rambling on when I've already made the points that I really wanted to make.
Me too - my posts tend to be too long for LW. I think it's a good idea to try to be a bit shorter and more succinct for both of us.
Apparently, the outcome of soccer matches between closely matched teams tend to be more unpredictable than matches between closely matched teams in other sports. So yeah, the only accurate answer the pundit could give to "Why did Man City win the final match?" would be along the lines of "On that day, things went right for them."
Great point, and certainly something I'll be on the lookout for.
There is, however, one possible defense in some cases: it could be that the smackdowns in history are the interesting cases and therefore the ones we talk about.
To illustrate using a different set of factors from Diamond, he also lists many factors explaining why Eurasia advanced so much faster than other regions. Maybe the reason we're comparing Eurasia to the rest of the world in the first place, rather than comparing Europe to Asia, North to South, or Old World to New World, is precisely because that was the split where the factors all lined up one way.
(I think this caveat is important to note in theory but actually implausible in the examples given. Especially in Pinker's case: the levels of violence throughout history would be pretty interesting even if they hadn't been in steady decline).
Another salient example I'm presently studying is taken from Steven Pinker's The Better Angels of Our Nature. I can provide you with the details on demand.
I'm interested in the details. Thanks.
In passing, I might mention that I think that the fact that moral debates are not one-sided indicates that moral realism is false, since if moral realism were true, moral facts should provide us with one-sided evidence on moral questions
Situations where "moral facts provide us with one-sided evidence" don't usually lead to moral debates. "Under ordinary circumstances, it's wrong to shoplift a candy bar from a convenience store" isn't particularly controversial.
I'm not saying that there are no uncontroversial moral issues. I'm saying that even moral positions that are wrong usually have something that tells in favour of them. This contrasts with the situation in science where outdated scientific theories (such as Aristotelian physics) no longer has any evidence that tells in its favour (that can't be explained away).
I'm not saying that it is impossible to find moral questions that are one-sided. What I am saying is that this is an uncommon pattern, and that this contrasts with the situation in science. My hypothesis is that the cause of this difference is that in science the evidence have a "common cause"-structure - they are all caused by the fact which they indicate - whereas in morality we have not - moral facts do not cause their evidence, or the arguments for them. This in turn indicates that there is no independent moral reality.
"Under ordinary circumstances, it's wrong to shoplift a candy bar from a convenience store" isn't particularly controversial.
I think that a lot of anarchists could present pretty substantial cases against that, actually.
Yes, and there also a lot of crackpots willing to present cases against physical positions that should be uncontroversial.
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Thanks. I tried to fix it but using your advice but it doesn't seem to work. What does it look like for you?
Basically, you're pasting in text with HTML tags which force a particular style.
Specifically, your paragraphs look like this:
<p style="margin-bottom: 12pt; text-align: justify;" class="MsoNormal"><span style="font-size: 12pt; font-family: 'Times New Roman', serif;">On questions of simple fact (for example, whether Earthly life arose by natural selection)
In passing, I might mention that I think that the fact that moral debates are not one-sided indicates that moral realism is false, since if moral realism were true, moral facts should provide us with one-sided evidence on moral questions,
At best that's a circular argument, since you're "observation" is that moral debates should not appear one-sided is based on an implicit premise similar to your conclusion.
No. It is based mainly on the fact that moral philosophers (rightly, in my view) use the reflective equilibrium method, where you weigh different intuitions and general principles against each other to arrive at moral judgements. This is precisely the sort of weighing of of pros and cons that we see in policy debates and which we don't see in one-sided questions such as how Earthly life arose. The intuition that this is the right method in ethics is not based on my meta-ethical views on the nature of morality and is indeed widely shared among moral philosophers that subscribe to different meta-ethical views.
This is precisely the sort of weighing of of pros and cons that we see in policy debates and which we don't see in one-sided questions such as how Earthly life arose.
Have you actually even looked into the state of our knowledge of how Earthly life arose? Last time I looked there were many competing theories and people were in fact weighing the evidence (such as it was) for and against each one.
In Policy Debates Should Not Appear One-Sided, Eliezer Yudkowsky argues that arguments on questions of fact should be one-sided, whereas arguments on policy questions should not:
On questions of simple fact (for example, whether Earthly life arose by natural selection) there's a legitimate expectation that the argument should be a one-sided battle; the facts themselves are either one way or another, and the so-called "balance of evidence" should reflect this. Indeed, under the Bayesian definition of evidence, "strong evidence" is just that sort of evidence which we only expect to find on one side of an argument.
But there is no reason for complex actions with many consequences to exhibit this onesidedness property.
The reason for this is primarily that natural selection has caused all sorts of observable phenomena. With a bit of ingenuity, we can infer that natural selection has caused them, and hence they become evidence for natural selection. The evidence for natural selection thus has a common cause, which means that we should expect the argument to be one-sided.
In contrast, even if a certain policy, say lower taxes, is the right one, the rightness of this policy does not cause its evidence (or the arguments for this policy, which is a more natural expression), the way natural selection causes its evidence. Hence there is no common cause of all of the valid arguments of relevance for the rightness of this policy, and hence no reason to expect that all of the valid arguments should support lower taxes. If someone nevertheless believes this, the best explanation of their belief is that they suffer from some cognitive bias such as the affect heuristic.
(In passing, I might mention that I think that the fact that moral debates are not one-sided indicates that moral realism is false, since if moral realism were true, moral facts should provide us with one-sided evidence on moral questions, just like natural selection provides us with one-sided evidence on the question how Earthly life arose. This argument is similar to, but distinct from, Mackie's argument from relativity.)
Now consider another kind of factual issues: multiple factor explanations. These are explanations which refer to a number of factors to explain a certain phenomenon. For instance, in his book Guns, Germs and Steel, Jared Diamond explains the fact that agriculture first arose in the Fertile Crescent by reference to no less than eight factors. I'll just list these factors briefly without going into the details of how they contributed to the rise of agriculture. The Fertile Crescent had, according to Diamond (ch. 8):
(Note that all of these factors have to do with geographical, botanical and zoological facts, rather than with facts about the humans themselves. Diamond's goal is to prove that agriculture arose in Eurasia due to geographical luck rather than because Eurasians are biologically superior to other humans.)
Diamond does not mention any mechanism that would make it less likely for agriculture to arise in the Fertile Crescent. Hence the score of pro-agriculture vs anti-agriculture factors in the Fertile Crescent is 8-0. Meanwhile no other area in the world has nearly as many advantages. Diamond does not provide us with a definite list of how other areas of the world fared but no non-Eurasian alternative seem to score better than about 5-3 (he is primarily interested in comparing Eurasia with other parts of the world).
Now suppose that we didn't know anything about the rise of agriculture, but that we knew that there were eight factors which could influence it. Since these factors would not be caused by the fact that agriculture first arose in the Fertile Crescent, the way the evidence for natural selection is caused by the natural selection, there would be no reason to believe that these factors were on average positively probabilistically dependent of each other. Under these conditions, one area having all the advantages and the next best lacking three of them is a highly surprising distribution of advantages. On the other hand, this is precisely the pattern that we would expect given the hypothesis that Diamond suffers from confirmation bias or another related bias. His theory is "too good to be true" and which lends support to the hypothesis that he is biased.
In this particular case, some of the factors Diamond lists presumably are positively dependent on each other. Now suppose that someone argues that all of the factors are in fact strongly positively dependent on each other, so that it is not very surprising that they all co-occur. This only pushes the problem back, however, because now we want an explanation of a) what the common cause of all of these dependencies is (it being very improbable that they all would correlate in the absence of such a common cause) and b) how it could be that this common cause increases the probability of the hypothesis via eight independent mechanisms, and doesn't decrease it via any mechanism. (This argument is complicated and I'd be happy on any input concerning it.)
Single-factor historical explanations are often criticized as being too "simplistic" whereas multiple factor explanations are standardly seen as more nuanced. Many such explanations are, however, one-sided in the way Diamond's explanation is, which indicates bias and dogmatism rather than nuance. (Another salient example I'm presently studying is taken from Steven Pinker's The Better Angels of Our Nature. I can provide you with the details on demand.*) We should be much better at detecting this kind of bias, since it for the most part goes unnoticed at present.
Generally, the sort of "too good to be true"-arguments to infer bias discussed here are strongly under-utilized. As our knowledge of the systematic and predictable ways our thought goes wrong increase, it becomes easier to infer bias from the structure or pattern of people's arguments, statements and beliefs. What we need is to explicate clearly, preferably using probability theory or other formal methods, what factors are relevant for deciding whether some pattern of arguments, statements or beliefs most likely is the result of biased thought-processes. I'm presently doing research on this and would be happy to discuss these questions in detail, either publicly or via pm.
*Edit: Pinker's argument. Pinker's goal is to explain why violence has declined throughout history. He lists the following five factors in the last chapter: