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… is from page 135 of the 1964 Harper Torchbooks edition of Karl Popper’s 1957 book, The Poverty of Historicism [2] (original emphasis):
And in the social sciences it is even more obvious than in the natural sciences that we cannot see and observe our objects before we have thought about them. For most of the objects of social science, if not all of them, are abstract objects; they are theoretical constructions.