popper-logic-scientific-discovery

310
new appendices
The first two of my new appendices contain three short notes, published
between 1933 and 1938, and closely connected with the book.
They do not read well, I am afraid: they are unduly compressed, and I
was unable to make them more readable without changes that would
have diminished their value as documents.
Appendices *ii to *v are somewhat technical—too much so for my
taste, at least. But these technicalities are necessary, it seems to me, in
order to solve the following philosophical problem. Is the degree of corroboration
or acceptability of a theory a probability, as so many philosophers have
thought? Or in other words, Does it obey the rules of the probability calculus?
I had answered this question in my book and my answer was, ‘No’.
To this some philosophers replied, ‘But I mean by probability (or by
corroboration, or by confirmation) something different from what
you mean’. To justify my rejection of this evasive reply (which
threatens to reduce the theory of knowledge to mere verbalism), it was
necessary to go into technicalities: the rules (‘axioms’) of the probability
calculus had to be formulated, and the part played by each of
them had to be found. For in order not to prejudge the issue whether
or not degree of corroboration is one of the possible interpretations of
the calculus of probability, this calculus had to be taken in its widest
sense, and only such rules admitted as were essential to it. I began these
investigations in 1935, and a brief report of some of my earlier investigations
is contained in appendix *ii. An outline of my more recent
results is given in appendices *iv and *v. In all these appendices it is
asserted that, apart from the classical, the logical, and the frequency
interpretations of probability, which were all dealt with in the book,
there are many different interpretations of the idea of probability, and of the mathematical
calculus of probability. They thus prepare the way for what I have later
called the propensity interpretation of probability. 2
2 Cf. my paper, ‘The Propensity Interpretation of Probability and the Quantum Theory’ in
Observation and Interpretation, ed. by S. Körner, 1957, pp. 65–70, and 88 f. See also the two
papers mentioned in the foregoing footnote, especially pp. 388 and 188, respectively.
* Since the first English edition of this book, two further papers of mine on propensity
have been published:
‘The Propensity Interpretation of Probability’ in The British Journal for the Philosophy of
Science 10, 1959, pp. 25–42.
‘Quantum Mechanics without “The Observer”’, in Quantum Theory and Reality, edited by
Mario Bunge, 1967, pp. 7–44. (See especially pp. 28–44.)