没看懂的问题

Krugman （2010）在“The New Economic Geography, Now Middle-aged”中，写到他建立模型的四个原理：其中两个(下面)，没看懂。请大家指点。谢谢。

Nodormitive properties: the reference is toMolie`re’s doctor, who triumphantly explains that opium puts people to sleepbecause of its dormitive properties. The economics equivalent is the assertionthat production clumps together because of agglomeration economies; I wanted toderive those agglomeration economies from something more fundamental, such asthe interaction among economies of scale, transportation costs and market size.This meant, among other things, downplaying invisible external economies likeinformation spillovers.

Distancebetween assumptions and conclusions: this is alittle hard to explain if you are not in the modeling business, but there is abroad sense, which I share, that you are learning more from a model if therabbit is not stuffed too visibly into the hat just before the theorist pullsit out. For that reason I did not follow FUJITA (1988) in assuming that thereare non-traded inputs produced with economies of scale; even if that is reasonablein many cases, it would be more interesting to show agglomeration emergingwithout such a strong assumption.

一个朋友的解答

英语世界很多人引用非安眠药性质来批评同义语反复的解释方式，“为什么说这种药是安眠药呢？因为它能够安眠”。对于聚集的同义反复的解释思路就是聚集经济理论，“为什么存在聚集呢？因为存在聚集经济”。克鲁格曼等人认为聚集经济理论对于聚集的解释太低级了，是同义语反复；克氏决定揭示更深层次的机制来解释聚集现象。