HL CHAPTER THREE What Is a Model? How Does It Work?

CHAPTER THREE What Is a Model? How Does It Work?
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FEW PH.D. ECONOMISTS today read Adam Smith—any more than modern physicists learn their stuff from Isaac Newton.
Note:I PADRI

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He went back to the classics, to see how a phenomenon as obvious to the untutored eye as the growth of knowledge had been handled systematically by earlier generations of economists.
Note:L ATTEGGIAMENTO DI ROMER NEL 1986

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the story begins with The Wealth of Nations.
Note:ANCHE NEL CASO DEI RENDIMENTI CRESCENTI

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stories about his absentmindedness abound. How he walked out for air in his nightshirt and didn’t stop for fifteen miles. How he thrust a slice of bread and butter into a teapot, poured in, waited, poured out—and complained of the quality of the tea.
Note:ADAM LO SVANITO

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Much sometimes is made of the fact that as a baby he was kidnapped by gypsies. They left him in the next town down the road;
Note:ADAMO

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At fourteen he was sent to the University of Glasgow, where the tradition of experimental demonstration was strong.
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No longer was it sufficient to explain the fall of stones or the rise of sparks by saying that it was “in their nature.”
Note:FINE DI ARISTOTELE

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Smith hated Oxford. There are several colorful passages in The Wealth of Nations in which he attacks the tenure system for having destroyed professors’ incentives to learn, or teach, or even meet their students.
Note:ACCADEMIA

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William Harvey was born in 1578,
Note:SOTTO....COSA SIGNIFICA SPIEGARE...COS È UN MODELLO

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The heart was conceived of by physicians and anatomists in those days, as it had been since the time of the physician Galen (first century A.D.), as resembling a furnace, or even the sun itself. The major organ of the body was thought to be the liver. It was there that food was turned into blood,
Note:I MEDICI DI ALLORA...ADORATORI DEL FEGATO

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Harvey concluded that the heart’s obvious heat was a secondary matter, that the muscle must serve as a pump rather than as a furnace
Note:POMPA O FORNACE?

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he showed that the heart pumps more blood into the arteries in half an hour—well over two gallons—than the entire body contains. Where else could it go but around in a circle?
Note:DIMOSTRAZ DI HARVEY...ARTERIE E VENE DOVEVANO ESSERE COLLEGATE DAI CAPILLARI

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they were infuriated by a model whose few simple assumptions brushed aside everything that they had struggled so laboriously to understand.
Note:REAZIONE DEI COLLEGHI

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Only with the invention of the microscope, some thirty years later, was the existence of the capillaries firmly established, exactly as Harvey had predicted.
Note:IL VENDICATORE DI H

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Gradually the new generation replaced the old.
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“Science advances funeral by funeral.”)
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Harvey’s calculations amounted to one of the first mathematical models in history
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“The Growth of Truth as Illustrated in the Discovery of the Circulation of the Blood,”
Note:LA CONFERENZA DI WILLIAM OSLER 1906

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It is thanks to these lectures that we know something about Smith’s views of what constitutes a satisfying explanation.
Note:LE LEZIONI DI EDINBURGO DI SMITH...IN PARTICOLARE L ASTRONOMIA

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“the discovery of an immense chain of the most important and sublime truths, all connected together by one capital fact [gravity], of which we have daily experience.”
Note:LA CATENA MECCANICA DI NEWTON....DIVIDIRE E COLLEGARE

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What we look for in an explanation, said Smith, is “a connecting principle” between apparently unrelated events.
Note:CONNECTIN PEOPLE

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Science is a search for the “invisible chains which bind together all these discordant objects”
Note:SCIENZA

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The enemy of good theory is promiscuous analogizing, Smith stated, the work of thinkers who endeavor to explain one thing in terms of another.
Note:ANALOGIA...IL NEMICO...ESEMPIO: I PITAGORICI SPIEGANO TUTTO IN TERMINI DI NUMERI

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Physicians were forever making extended parallels between physiology and the “body politic”
Note:ANATOMIA E POLITICA

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“Money is the Fat of the Body-politick, whereof too much doth often hinder its agility, as too little makes it sick…”).
Note:ESEMPIO DI PETTY

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“There is no break, no stop, no gap, no interval.”
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if it cannot be said in plain language, said Smith, it probably is not right.
Note:SEMPLICOTÀ

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His reputation is as among the most mathematical of the new generation.
Note:SALE SYL PALCO ROMER...IL PIÙ ATTESO

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it placed him in opposition not only to his teacher Lucas but to the entire Chicago tradition of taking perfect competition as its most fundamental assumption.
Note:IL NUOVO LAVORO DI ROMER SUI RENDIMENTI CRESCENTI ...1990

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Romer has been insistent all along about the power of mathematical methods. They state problems more clearly and solve them with greater clarity and persuasive power
Note:LA FEDELE COMPAGNA

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logic and evidence “have a power that transcends the wishes, beliefs and preferences of the people who use them.
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“Why Indeed in America? Theory, History and the Origins of Modern Economic Growth.”
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“these equations are so simplistic and the world is so complicated.”
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equations “don’t tell us anything new.”
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Modelers focus on the issues that are easy to formalize, and defer the more difficult issues for a later day,
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“The sensible approach is not to shut down the development of formal theory, but to tolerate a division of labor in which natural language and formal theorizing continue in parallel. Specialists in each camp can address those issues in which they have a comparative advantage and periodically compare notes.”
Note:LA SOLUZIONE ROMER

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Romer borrows the familiar example of the steam engine. A famously bad explanation offered by an engineer in the mid-nineteenth century ascribed its motion to a “force locomotif” (in a similar way Aristotle had attributed the fall of stones to their “inner nature”). A more satisfying explanation says Romer, divides the steam engine into component parts—firebox, boiler, steam governor, and so on—in order to account for the working of the locomotive overall. “What theories do for us is take all the complicated information we have about the world and organize it into this kind of a hierarchical structure,”
Note:LA SPIEGA SCIENTIFICA....SCOMPORRE...RIDURRE

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The “old” growth theory associated with Robert Solow
Note:IL NEMICO DI ROMER

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There are conventional economic inputs. And there is “exogenous” technology,
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technology can be employed by any number of persons at the same time.
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For the purposes of the analysis, technology is viewed as being essentially a public good, freely available to anyone who wants some.
Note:L IMPLICITO IN SOLOW

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The government provides it, through universities.
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New growth theory divides the world along different lines—into “instructions” and “materials,”
Note:LA LANCIA VITÀ

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“instructions” will become “ideas” and “materials” will become “things.”
Note:NEL PAPER SUCCESSIVO

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atoms and bits
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The key distinction, he says, is no longer between public and private but between rival and nonrival goods
Note:ALTRA ALTRE VITÀ

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Humans use non-rival instructions together with rival goods (like pots, pans or machine tools) to transform other rival goods, rearranging them into new configurations that are more valuable than the old ones.
Note:IL PROCESSO

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Since an idea can be copied and used over and over, its value increases in proportion to the quantity of the rival materials it can be used to transform: the larger the market, the greater the payoff to a new idea. More widgets can be sold in a big city than in a small town,
Note:IL FRUTTO DI UN IDEA

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The new ideas have not yet found the proper path to widespread understanding. The natural resistance to them is great.
L ESITO DELLA PRIMA PRESENTAZIONE