In The Structure of Scientific Revolutions, Thomas S. Kuhn proposed a philosophy of science, whose validity he justified by an appeal to the history of science. Kuhn is completely unaware of the circularity of his method. The circularity of Kuhn's reasoning is particularly damaging to his case if one considers for a moment that historical knowledge itself is part of scientific knowledge. The notion of colligation introduces confusion. Single events cannot be colligated to one another unless somebody has done the colligating. The two postulates that concern the problem of circularity in historical composition are: the 'Postulate of Sufficient Variety', and the 'Postulate of Sufficient Specification'. Imre Lakatos stated that the philosophy of science without history is empty and that the history of science without philosophy of science is blind.