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As another simple instance, it may be pointed out that in accor-
dance with the principles of deductive political economy, the repeal of
the Corn Laws must have tended to bring about a permanent fall in the
price of wheat in England. Yet no such fall occurred immediately. The
explanation of the apparent discrepancy is to lie found in the interfer-
ence of such circumstances as the failure of the potato crop, the Crimean
War, and especially the depreciation of gold, which contributed to main-
tain the price up to 1862, notwithstanding free trade. Time, moreover,
was required in order to allow the area of cultivation in new countries to
be increased, and means of communication to be developed, so as to
meet the new demand.137
§4. Ricardo s use of the deductive method. The above consider-
ations indicate certain requirements that need to be satisfied in the right
use of the deductive method, and also certain limitations to which the
method is subject. One essential point is that there shall be a clear and
The Scope and Method of Political Economy/109
definite enunciation of the assumptions upon which any given piece of
reasoning is based. Sometimes, in addition to giving a careful explana-
tion of the conditions under which the inferred results hold good, it will
be advantageous to indicate the directions in which these results are
likely to be modified by alterations in the conditions. In discussing the
effects of economic changes it is further requisite to specify in general
terms the period of time taken into consideration, distinguishing clearly
between immediate and ultimate effects. It must always be remembered
that assumptions need to be varied in order to meet varying economic
circumstances; and a priori dogmatism must be avoided in regard to the
application of conclusions to any given state of society. Before such
applications can be justified, empirical tests must be applied tests,
which in some cases lie ready enough to hand, but which not infre-
quently involve systematic observation and statistical research of greater
difficulty than the deductive reasoning itself.
Ricardo s writings, and in particular his Principles of Political
Economy and Taxation, are frequently quoted as affording typical and
representative examples of the use of the deductive method in econom-
ics; and any objections, to which either his methods or his results are
open, are accordingly regarded as in all respects equivalent to objec-
tions to the deductive method as such. It must be said, however, that
while Ricardo s writings contain some of the most brilliant and instruc-
tive examples of close deductive reasoning to be found in economic
literature, and while a thorough study and mastery of his works may
rightly be regarded as a part of the necessary equipment of the economic
student, still his manner of employing the deductive method is not free
from grave faults. For instance, the explanations and qualifications, which
are continually necessary in the interpretation of his results, have usu-
ally to be supplied by the reader himself. Neither the subsidiary postu-
lates, nor those that underlie the greater part of the reasoning, are ex-
plicitly indicated; and there is sometimes an unexplained change from
one hypothesis to another that is specially perplexing. Again, the neces-
sity of attending to the element of time is insufficiently emphasized, and
far too little importance seems to be attached to the characteristics of
the periods of transition, during which the ultimate effects of economic
causes are working themselves out. The tone adopted by Ricardo sug-
gests further an undue confidence in the absolute and universal validity
of the conclusions reached; and in his illustrations there is a remoteness
from the facts of actual life that is not really essential to the employment
110/John Neville Keynes
of the deductive method.
There is still another respect in which Ricardo s chief work fails to
satisfy the requirements of a perfect deductive system. As a science
grows more deductive, the logical arrangement of its different parts,
and the due subordination of some parts to. others, become consider-
ations of increasing importance. Ricardo, however, never makes suffi-
ciently clear the exact relation between his different theorems, and the
manner of their dependence one upon another. In some respects, the
different chapters of the Principles of Political Economy and Taxation
read more like independent essays than consecutive chapters of a con-
nected and logically complete system.
An explanation of much of the above is to be found in the special
circumstances and conditions under which Ricardo wrote. While his
premisses were suggested by the actual economic world in which he
lived, his observation was partial, and confined to a narrow range. Be
was consequently led to interpret his results without adequate limita-
tion. It is, moreover, very doubtful whether it was his deliberate inten-
tion to produce a complete systematic exposition of economic science.
It has been suggested on very plausible grounds that his chief work was
originally written not for publication, but with the object of formulating
his own ideas on various economic questions, and for private circula-
tion amongst an inner circle of acquaintances. If this view is correct, the
not infrequent incompleteness of the argument from the strictly logical
standpoint is to a considerable extent accounted for. Nothing can be
more natural than that anyone writing for those whom he knows to be
already familiar with his general attitude should omit an explicit state-
ment of postulates and qualifications, that are certain in any case to be
present to the minds of his readers.138
Whatever may be the explanation, however, of Ricardo s shortcom-
ings, it is certain that the deductive method is not exemplified in any-
thing approaching an ideal form in his pages.
§ 5. The premises deductive political economy. In those abstract
reasonings, which constitute the most prominent part of economic theory,
the principles by which the economist is guided in his choice of pre-
misses are generality and simplicity: the former, in order to widen as far
as possible the range over which the theory may be applicable as an
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