Thus I see the problem of knowledge in a different way from that of my predecessors. Security and justification of claims to knowledge are not my problem. Instead, my problem is the growth of knowledge: in which sense can we speak of the growth or the progress of knowledge, and how can we achieve it? 
In upholding an objective third world [World 3] I hope to provoke those whom I call ‘belief philosophers’: those who, like Descartes, Locke, Berkeley, Hume, Kant, or Russell, are interested in our subjective beliefs, and their basis or origin. Against these belief philosophers I urge that our problem is to find better and bolder theories; and that critical preference counts, but not belief. 
The commonsense theory of knowledge (which I have also dubbed ‘the bucket theory of the mind’) is the theory most famous in the form of the assertion that ‘there is nothing in our intellect which has not entered it through the senses’. (I have tried to show that this view was first formulated by Parmenides—in a satirical vein: Most mortals have nothing in their erring intellect unless it got there through their erring senses.) 
The phenomenon of human knowledge is no doubt the greatest miracle in our universe. It constitutes a problem that will not soon be solved, and I am far from thinking that the preset volume makes even a small contribution to its solution. But I hope that I have helped to restart a discussion which for three centuries has been bogged down in preliminaries.
Since Descartes, Hobbes, Locke, and their school, which includes not only David Hume but also Thomas Reid, the theory of human knowledge has been largely subjectivist: knowledge has been regarded as a specially secure kind of human belief, and scientific knowledge as a specially secure kind of human knowledge.
The essays in this book break with a tradition that can be traced back to Aristotle—the tradition of this commonsense theory of knowledge. I am a great admirer of common sense which, I assert, is essentially selfcritical. But while I am prepared to uphold to the last the essential truth of commonsense realism, I regard the commonsense theory of knowledge as a subjectivist blunder. This blunder has dominated Western philosophy. I have made an attempt to eradicate it, and to replace it by an objective theory of essentially conjectural knowledge. This may be a bold claim but I do not apologize for it. [Preface]
Earlier I said that Popper believed in absolute and objective truth. This is very easily misunderstood, especially if we equate a definition of ‘truth’ with a criterion of truth. But whether or not truth is absolute has nothing whatsoever to do with whether or not we have a criterion for determining what it is. ‘Absolute’ simply means that something is not conditional or relative to anything else. Popper thought that truth is absolute in just this sense. Being true is different from being-believed-to-be true. It is not relative to or conditioned by what anyone believes. And it does not depend upon a theory, or evidence, or a historical context, or anything else—except the facts. 
My first thesis involves the existence of two different senses of knowledge or of thought: (1) knowledge or thought in the subjective sense, consisting of a state of mind or of consciousness or a disposition to behave or to react, and (2) knowledge in an objective sense, consisting of problems, theories, and arguments as such. Knowledge in this objective sense is totally independent of anybody’s claim to know; also it is independent of anybody’s belief, or disposition to assent; or to assert, or to act. Knowledge in the objective sense is knowledge without a knower: it is knowledge without a knowing subject.
Of thought in the objective sense Frege wrote: ‘I understand by a thought not the subjective act of thinking but its objective content…’. [108-9]