  Hempel (1945) and Carnap (1950) each distinguished two different ‘concepts’ of confirmation: the ‘classificatory’ or ‘qualitative’ concept on the one hand and the ‘quantitative’ concept on the other. Roughly, the classificatory concept is employed in the making of yes-or-no judgements about whether a given piece of evidence does or does not support a given hypothesis.  Thus, it is the classificatory concept which is in play when one is concerned with judgements of the following form: ‘Hypothesis H is confirmed by evidence E’. On the other hand, the quantitative concept is employed in making numerical judgements about how much support a hypothesis derives from a given piece of evidence (e.g,. ‘Hypothesis H is confirmed by evidence E to degree  R’).[19]  Formal theories attempting to explicate each of these notions were developed. Hempel (1945) took the lead in attempting to explicate the qualitative concept while Carnap (1950, 1952) concentrated on the quantitative concept. During this period, the philosophical study of the relationship between evidence and theory took on, perhaps for the first time, the characteristics of something like normal science, and became a discipline replete with technical problems, puzzles, and paradoxes, the anticipated solutions to which were viewed as items on the agenda for future  research.[20]  Here lie the origins of present-day confirmation theory, as represented by Bayesianism in its protean forms (See, e.g., Jeffrey 1965, 1992, 2004, Horwich 1983, Howson and Urbach 1993) and its rivals (e.g., Glymour's (1980) ‘bootstrapping’ model of confirmation).