The Growth of Human Knowledge

For Popper accordingly, the growth of human knowledge proceeds from our
problems and from our attempts to solve them. These attempts involve the
formulation of theories which, if they are to explain anomalies which exist
with respect to earlier theories, must go beyond existing knowledge and
therefore require a leap of the imagination. For this reason, Popper places
special emphasis on the role played by the independent creative imagination
in the formulation of theory. The centrality and priority of problems in
Popper's account of science is paramount, and it is this which leads him to
characterise scientists as roblem-solvers'. Further, since the scientist
begins with problems rather than with observations or are facts', Popper
argues that the only logical technique which is an integral part of
scientific method is that of the deductive testing of theories which are not
themselves the product of any logical operation. In this deductive procedure
conclusions are inferred from a tentative hypothesis. These conclusions are
then compared with one another and with other relevant statements to
determine whether they falsify or corroborate the hypothesis. Such
conclusions are not directly compared with the facts, Popper stresses,
simply because there are no ure' facts available; all
observation-statements are theory-laden, and are as much a function of
purely subjective factors (interests, expectations, wishes, etc.) as they
are a function of what is objectively real.

How then does the deductive procedure work? Popper specifies four steps:

    (a) The first is formal, a testing of the internal consistency of the
theoretical system to see if it involves any contradictions.

    (b) The second step is semi-formal, the axiomatising of the theory to
distinguish between its empirical and its logical elements. In performing
this step the scientist makes the logical form of the theory explicit.
Failure to do this can lead to category-mistakes - the scientist ends up
asking the wrong questions, and searches for empirical data where none are
available. Most scientific theories contain analytic (i.e. a priori) and
synthetic elements, and it is necessary to axiomatise them in order to
distinguish the two clearly.

(c) The third step is the comparing of the new theory with existing ones to
determine whether it constitutes an advance upon them. If it does not
constitute such an advance, it will not be adopted. If, on the other hand,
its explanatory success matches that of the existing theories, and
additionally, it explains some hitherto anomalous phenomenon, or solves some
hitherto unsolvable problems, it will be deemed to constitute an advance
upon the existing theories, and will be adopted. Thus science involves
theoretical progress. However, Popper stresses that we ascertain whether one
theory is better than another by deductively testing both theories, rather
than by induction. For this reason, he argues that a theory is deemed to be
better than another if (while unfalsified) it has greater empirical content,
and therefore greater predictive power than its rival. The classic
illustration of this in physics was the replacement of Newton's theory of
universal gravitation by Einstein's theory of relativity. This elucidates
the nature of science as Popper sees it: at any given time there will be a
number of conflicting theories or conjectures, some of which will explain
more than others. The latter will consequently be provisionally adopted. In
short, for Popper any theory X is better than a ival' theory Y if X has
greater empirical content, and hence greater predictive power, than Y.

    (d) The fourth and final step is the testing of a theory by the
empirical application of the conclusions derived from it. If such
conclusions are shown to be true, the theory is corroborated (but never
verified). If the conclusion is shown to be false, then this is taken as a
signal that the theory cannot be completely correct (logically the theory is
falsified), and the scientist begins his quest for a better theory. He does
not, however, abandon the present theory until such time as he has a better
one to substitute for it. More precisely, the method of theory-testing is as
follows: certain singular propositions are deduced from the new theory -
these are predictions, and of special interest are those predictions which
are isky' (in the sense of being intuitively implausible or of being
startlingly novel) and experimentally testable. From amongst the latter the
scientist next selects those which are not derivable from the current or
existing theory - of particular importance are those which contradict the
current or existing theory. He then seeks a decision as regards these and
other derived statements by comparing them with the results of practical
applications and experimentation. If the new predictions are borne out, then
the new theory is corroborated (and the old one falsified), and is adopted
as a working hypothesis. If the predictions are not borne out, then they
falsify the theory from which they are derived. Thus Popper retains an
element of empiricism: for him scientific method does involve making an
appeal to experience. But unlike traditional empiricists, Popper holds that
experience cannot determine theory (i.e. we do not argue or infer from
observation to theory), it rather delimits it: it shows which theories are
false, not which theories are true. Moreover, Popper also rejects the
empiricist doctrine that empirical observations are, or can be, infallible,
in view of the fact that they are themselves theory-laden.

The general picture of Popper's philosophy of science, then is this: Hume's
philosophy demonstrates that there is a contradiction implicit in
traditional empiricism, which holds both that all knowledge is derived from
experience and that universal propositions (including scientific laws) are
verifiable by reference to experience. The contradiction, which Hume himself
saw clearly, derives from the attempt to show that, notwithstanding the
open-ended nature of experience, scientific laws may be construed as
empirical generalisations which are in some way finally confirmable by a
ositive' experience. Popper eliminates the contradiction by rejecting the
first of these principles and removing the demand for empirical verification
in favour of empirical falsification in the second. Scientific theories, for
him, are not inductively inferred from experience, nor is scientific
experimentation carried out with a view to verifying or finally establishing
the truth of theories; rather, all knowledge is provisional, conjectural,
hypothetical - we can never finally prove our scientific theories, we can
merely (provisionally) confirm or (conclusively) refute them; hence at any
given time we have to choose between the potentially infinite number of
theories which will explain the set of phenomena under investigation. Faced
with this choice, we can only eliminate those theories which are
demonstrably false, and rationally choose between the remaining, unfalsified
theories. Hence Popper's emphasis on the importance of the critical spirit
to science - for him critical thinking is the very essence of rationality.
For it is only by critical thought that we can eliminate false theories, and
determine which of the remaining theories is the best available one, in the
sense of possessing the highest level of explanatory force and predictive
power. It is precisely this kind of critical thinking which is conspicuous
by its absence in contemporary Marxism and in psychoanalysis.