 For Popper, the growth of human knowledge proceeds from our problems and from our attempts to solve them. These attempts involve the formulation of theories which must go beyond existing knowledge and therefore require a leap of the imagination. For this reason, he places special emphasis on the role played by the creative imagination in theory formulation. The priority of problems in Popper’s account of science is paramount, and it is this which leads him to characterise scientists as “problem-solvers”. Further, since the scientist begins with problems rather than with observations or “bare facts”, he 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 and 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 “pure” 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.