<p>Toward the end of the nineteenth century, Ernst Mach expressed his worries about obscurities and metaphysical elements in scientific knowledge, and consequently contributed to the development of a Viennese tradition. Later on, Vienna Circle further extended Mach's ideas and led to the development of the logical positivist movement. Among the main tenets of this movement is the view that scientific theories are to be reduced to an empirical base capable of conclusive verification. But scientific theories are usually based on unverified and occasionally unverifiable hypotheses and principles. Thus, once this is realized, positivism in spite of itself will contribute to the development of scepticism about scientific knowledge.</p> <p>In reaction to the verificationism, however, Karl Popper developed his thesis of falsificationism or fallibilism; but this principle also leads to scepticism at least about certainty claims, with far reaching consequences. This chain of events leads to the development of Paul Feyerabend's epistemological anarchisma a rejection of all rules and methods in science in an attempt to reduce science to the level of irrationality and mythology.</p> <p>Against the negativist conclusions of these positions about science, the integrity of scientific knowledge is defended in this thesis. It is shown how scientific knowledge can be defended against scepticism of the type to which verificationism tends: this is done by examining one recent and rigorous sceptical position which undermines not only certainty and rationality of knowledge claims, but the very possibility of knowledge. By examining Popper's fallibilism, it is shown that science can also be defended against the negativist conclusions of fallibilism. Similarly, it is shown that Feyerabend's epistemological anarchism cannot either undermine scientific knowledge.</p> <p>These negativist positions, though they have received strong criticisms in some quarters, yet have not been examined all together, from the standpoint of their impact on the integrity of scientific knowledge. This task is undertaken in this thesis; we thus arrive at a positive and correct evaluation of scientific knowledge in the context of contemporary negativist epistemological trends. It has been shown that in spite of all the negativist arguments of the above positions, we can obtain certainty, justification, and truth in science, and thus we can obtain knowledge. But my rejection of negativism in science does not entail, and should not be construed as an advocacy of a return to, positivism.</p> / Thesis / Doctor of Philosophy (PhD)