This paper is on the sources of knowledge. Beginning with the distinction of sources of knowledge in the genetic and methodological sense, and following Ajdukiewicz, a scheme of a more detailed analysis is outlined. As a result, apriorism and aposteriorism are divided into moderate and radical. The author offers a defense of moderate aposteriorism as the most proper epistemological solution. To argue for moderate aposteriorism requires a re-interpretation of the analytic/synthetic distinction that was attacked by Quine. However, there is a possibility of a reconciliation between naturalism and semantic holism -the views that were simultaneously held by Quine - and the dualism of analytic and synthetic sentences. This possibility is provided by a wide understanding of analyticity. On this approach a priori sentences are identified with analytic statements. However, although the laws of logic can be considered as absolute analyticals, no a priori sentences are absolute. The distinction is explained by the concept of apriorization. Finally, the status of logic is investigated in frameworks of aposteriorism. In consequence, no conflict arises between the thesis that all knowledge is derived from experience and the view that all logic is certain.