The theory of the measure to which evidence supports a theory. A fully formalized confirmation theory would dictate the degree of confidence that a rational investigator might have in a theory, given some body of evidence. The grandfather of confirmation theory is Leibniz, who believed that a logically transparent language of science would be able to resolve all disputes. In the 20th century a fully formal confirmation theory was a main goal of the logical positivists, since without it the central concept of verification by empirical evidence itself remains distressingly unscientific. The principal developments were due to Carnap, culminating in his Logical Foundations of Probability (1950). Carnap’s idea was that the measure needed would be the proportion of logically possible states of affairs in which the theory and the evidence both hold, compared to the number in which the evidence itself holds (see also range theory of probability). It therefore demands that we can put a measure on the ‘range’ of possibilities consistent with theory and evidence, compared with the range consistent with the evidence alone. Among the obstacles the enterprise meets is the fact that while evidence covers only a finite range of data, the hypotheses of science may cover an infinite range. In addition, confirmation proves to vary with the language in which the science is couched, and the Carnapian programme has difficulty in separating genuinely confirming variety of evidence from less compelling repetition of the same experiment. Confirmation also proved to be susceptible to acute paradoxes (see Goodman’s paradox, Hempel’s paradox). Finally, scientific judgement seems to depend on such intangible factors as the problems facing rival theories, and most workers have come to stress instead the historically situated sense of what looks plausible, characteristic of a scientific culture at a given time. See also limited independent variety, principle of, range theory of probability.