It has been pointed out by Carnap that ‘probability’ is an equivocal term, which is used currently in two senses: (i) the degree to which it is rational to believe a hypothesis h on specified evidence e, and (ii) the relative frequency (in an indefinitely long run) of one property of events or things with respect to another. This paper is concerned only with the first of these two senses, which will be referred to as ‘the concept of confirmation,’ in order to avoid equivocation.
We may distinguish a quantitative and a comparative concept of confirmation. The general form of statements involving the former is
The degree of confirmation of the proposition h, given the proposition
e as evidence, is r (where r is a real number between 0 and 1).
In this paper the notation for a statement of this form is
The general form of statements involving the comparative concept is The proposition h is equally or less confirmed on e than is the proposition h′ on e′,
which may be symbolized as
The following abbreviations will also be used in discussing comparative confirmation:
The former of these two abbreviations means intuitively
The proposition h is less confirmed on evidence e than h′ is on e′. The latter means
The proposition h is confirmed on evidence e to the same degree that h′ is on e′.
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