were always equally efficient, there would be no limit to the amount
producible. If the supply of food and raw materials can be multiplied,
wealth can be multiplied to any amount. The admitted tendency of
profits to fall must therefore be explained simply and solely by the
growing difficulty of producing the food and the raw material.

Ricardo's doctrine, then, is Malthus carried out more logically. Take
a nation in a state of industrial equilibrium. The produce of the
worst soil just supports the labourer, and leaves a profit to the
capitalist. The labourer gets just enough to keep up his numbers to
the standard; the capitalist just enough profit to induce him to keep
up the capital which supports the labourer. Since there can be only
one rate of wages and only one rate of profit, this fixes the shares
into which the whole produce of the nation is divided, after leaving
to the landlord the surplus produce of the more fertile soils.
Accepting this scheme as a starting-point, we get a method for
calculating the results of any changes. We can see how a tax imposed
upon rents or profits or wages will affect the classes which are thus
related; how improvements in cultivation or machinery, or a new demand
for our manufactures, will act, assuming the conditions implied in
this industrial organisation; how, in short, any disturbance of the
balance will work, so as to produce a new equilibrium. Ricardo exerts
all his ingenuity in working out the problem which, with the help of a
few assumptions, becomes mathematical. The arithmetical illustrations
which he employed for the purpose became a nuisance in the hands of
his disciples. They are very useful as checks to general statements,
but lend themselves so easily to the tacit introduction of erroneous
assumptions as often to give a totally false air of precision to the
results. Happily I need not follow him into that region, and may omit
any consideration of the logical value of his deductions. I must be
content to say that, so far as he is right, his system gives an
economic calculus for working out the ultimate result of assigned
economic changes. The pivot of the whole construction is the 'margin
of cultivation'--the point at which the food for a pressing population
is raised at the greatest disadvantages. 'Profits,' as he says,[319]
'depend on high and low wages; wages on the price of necessaries; and
the price of necessaries chiefly on the price of food, because all
other re