The Dictionary of Human Geography

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is primarily associated with the French School

ofhuman geographythat had its roots in the

writings of Paul Vidal de la Blache (1845–

1918), but also found favour in Britain in the

early-twentieth-century work of Patrick

Geddes and H.J. Fleure, and in the USA in

Carl Ortin Sauer’s insistence on the trans-

formative power of humanculture(see also

berkeley school). It thus stands in contrast

toenvironmental determinismand was clas-

sically expressed in Lucien Febvre’s dictum

‘There are no necessities, but everywhere pos-

sibilities; and man, as master of the possibil-

ities, is the judge of their use’ (Febvre, 1932,

p. 27). Different philosophical roots of the

doctrine have been identified, including neo-

Kantian philosophy (see kantianism:

Berdoulay, 1976), probability theory associ-

ated with Poincare ́(Lukermann, 1965), and

Lamarckian biology (see lamarck(ian)ism:

Archer, 1993). Differences between possibi-

lism, environmental determinism and prob-

abilism are more easily identified when taken

asideal typesrather than as operational per-

spectives in geographical research. dnl

Suggested reading

Lukermann (1965).

Postan thesis A major interpretation of the

dynamic of the medievaleconomy, proposed

by historian Michael Postan (1898–1981).

The thesis was first developed for England,

but subsequently extended to cover much of

Westerneurope. Postan’s ideas derived from

classical political economy, particularly

Ricardo and Malthus, which he saw as a

framework for understanding the links

between population, landedresourcesand

living standards over the long term (Postan,

1966, 1972; Hatcher and Bailey, 2001; see

malthusian model). In so doing, he reacted

negatively to linear interpretations of the

medieval economy that were underwritten by

a belief in the progressive growth of themar-

ket and monetization as frameworks for

understanding change. Indeed, the thesis was

eventually utilized as a means of understand-

ing both European medieval and early modern

pre-industrial economies (Le Roy Ladurie,

1966; Abel, 1980).

Postan accepted classical political economic

assumptions about the fixity of land supply as

a factor of production, minimal technological

innovation in farming and diminishing returns

to increased labour inputs. As a result, he

viewed population growth to be unsustainable

in the long term, as it led to an oversupply of

labour on the land and fragmentation of land

holdings. Consequently, he argued that as a

result of population growth over the thir-

teenth century, associated with real wage falls

and shrinkage of holding sizes, an increasingly

harvest-sensitive population emerged that was

vulnerable to periodic crises (Postan and

Titow, 1958–9). These were observable in a

consistent tendency for death rates to rise

with grain prices and responsible for cataclys-

mic phases such as the Great European

famine of 1315–22. Furthermore, he was

inclined to see susceptibility to high death

rates associated withepidemicdisease such

as the Black Death as a manifestation of

society’s vulnerability resulting from an

imbalance between population and resource

available per capita. Postan added other

elements to this interpretation, such as a belief

in the decline of soil fertility that arose as

populations cropped land too frequently and

nitrogen levels plummeted, driving communi-

ties to cultivate soil types that were inherently

unsuitable for arable farming and grain

production. He believed that population

decline in the fourteenth century was a

punishment for ‘overfishing’ in the previous

century, and that the damage done to soil

fertility was not repaired until at least the

sixteenth century when population totals

began again to recover.

Since Postan’s death, historians and histor-

ical geographers have contested the idea that

technology was unchanging and argued that

the thirteenth- and early fourteenth-century

economy was showing signs of developing spe-

cialization and genuinecomparative advan-

tages in a manner more consistent with

Smithian growth theory (Britnell, 1993;

Britnell and Campbell, 1995). It has also been

argued, in conformity with the boserup

thesis, that in densely populated areas of

England grain yields were increased by an

increase in labour inputs as land was cropped,

weeded and fertilised more frequently

(Campbell, 1983, 2000). Others have sought

alternative explanations for weakness in the

economy associated with seigneurial exploit-

ation through the removal of surpluses legit-

imated by serfdom as a relation of production

(seebrenner thesis). More recently, it has

been claimed that the difficulties associated

with harvest failure were in many instances

caused by extreme natural events that would

have impacted adversely on any pre-industrial

economy (Bailey, 1992). It has also been

argued that exogenously generated epidemic

disease that brought down population

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POSTAN THESIS